Gleam fix

14 files changed, 905 insertions, 1421 deletions

diff --git a/src/gleam/base.gleam b/src/gleam/base.gleam
index 7ec1558..a084a7c 100644
--- a/src/gleam/base.gleam
+++ b/src/gleam/base.gleam
@@ -11,15 +11,9 @@ pub fn encode64(input: BitString, padding: Bool) -> String {
   }
 }
 
-if erlang {
-  external fn do_encode64(BitString) -> String =
-    "base64" "encode"
-}
-
-if javascript {
-  external fn do_encode64(BitString) -> String =
-    "../gleam_stdlib.mjs" "encode64"
-}
+@external(erlang, "base64", "encode")
+@external(javascript, "../gleam_stdlib.mjs", "encode64")
+fn do_encode64(a: BitString) -> String
 
 /// Decodes a base 64 encoded string into a `BitString`.
 ///
@@ -31,15 +25,9 @@ pub fn decode64(encoded: String) -> Result(BitString, Nil) {
   do_decode64(padded)
 }
 
-if erlang {
-  external fn do_decode64(String) -> Result(BitString, Nil) =
-    "gleam_stdlib" "base_decode64"
-}
-
-if javascript {
-  external fn do_decode64(String) -> Result(BitString, Nil) =
-    "../gleam_stdlib.mjs" "decode64"
-}
+@external(erlang, "gleam_stdlib", "base_decode64")
+@external(javascript, "../gleam_stdlib.mjs", "decode64")
+fn do_decode64(a: String) -> Result(BitString, Nil)
 
 /// Encodes a `BitString` into a base 64 encoded string with URL and filename safe alphabet.
 ///
diff --git a/src/gleam/bit_builder.gleam b/src/gleam/bit_builder.gleam
index 960d665..03f0bff 100644
--- a/src/gleam/bit_builder.gleam
+++ b/src/gleam/bit_builder.gleam
@@ -13,22 +13,19 @@
 //// On Erlang this type is compatible with Erlang's iolists.
 
 import gleam/string_builder.{StringBuilder}
+@target(javascript)
+import gleam/list
+@target(javascript)
+import gleam/bit_string
 
-if javascript {
-  import gleam/list
-  import gleam/bit_string
-}
-
-if erlang {
-  pub external type BitBuilder
-}
+@target(erlang)
+pub type BitBuilder
 
-if javascript {
-  pub opaque type BitBuilder {
-    Bits(BitString)
-    Text(StringBuilder)
-    Many(List(BitBuilder))
-  }
+@target(javascript)
+pub opaque type BitBuilder {
+  Bits(BitString)
+  Text(StringBuilder)
+  Many(List(BitBuilder))
 }
 
 /// Create an empty `BitBuilder`. Useful as the start of a pipe chaning many
@@ -73,20 +70,15 @@ pub fn append_builder(
   do_append_builder(first, second)
 }
 
-if erlang {
-  external fn do_append_builder(
-    to: BitBuilder,
-    suffix: BitBuilder,
-  ) -> BitBuilder =
-    "gleam_stdlib" "iodata_append"
-}
+@target(erlang)
+@external(erlang, "gleam_stdlib", "iodata_append")
+fn do_append_builder(to to: BitBuilder, suffix suffix: BitBuilder) -> BitBuilder
 
-if javascript {
-  fn do_append_builder(first: BitBuilder, second: BitBuilder) -> BitBuilder {
-    case second {
-      Many(builders) -> Many([first, ..builders])
-      _ -> Many([first, second])
-    }
+@target(javascript)
+fn do_append_builder(first: BitBuilder, second: BitBuilder) -> BitBuilder {
+  case second {
+    Many(builders) -> Many([first, ..builders])
+    _ -> Many([first, second])
   }
 }
 
@@ -116,15 +108,13 @@ pub fn concat(builders: List(BitBuilder)) -> BitBuilder {
   do_concat(builders)
 }
 
-if erlang {
-  external fn do_concat(List(BitBuilder)) -> BitBuilder =
-    "gleam_stdlib" "identity"
-}
+@target(erlang)
+@external(erlang, "gleam_stdlib", "identity")
+fn do_concat(a: List(BitBuilder)) -> BitBuilder
 
-if javascript {
-  fn do_concat(builders: List(BitBuilder)) -> BitBuilder {
-    Many(builders)
-  }
+@target(javascript)
+fn do_concat(builders: List(BitBuilder)) -> BitBuilder {
+  Many(builders)
 }
 
 /// Joins a list of bit strings into a single builder.
@@ -135,17 +125,15 @@ pub fn concat_bit_strings(bits: List(BitString)) -> BitBuilder {
   do_concat_bit_strings(bits)
 }
 
-if erlang {
-  external fn do_concat_bit_strings(List(BitString)) -> BitBuilder =
-    "gleam_stdlib" "identity"
-}
+@target(erlang)
+@external(erlang, "gleam_stdlib", "identity")
+fn do_concat_bit_strings(a: List(BitString)) -> BitBuilder
 
-if javascript {
-  fn do_concat_bit_strings(bits: List(BitString)) -> BitBuilder {
-    bits
-    |> list.map(fn(b) { from_bit_string(b) })
-    |> concat()
-  }
+@target(javascript)
+fn do_concat_bit_strings(bits: List(BitString)) -> BitBuilder {
+  bits
+  |> list.map(fn(b) { from_bit_string(b) })
+  |> concat()
 }
 
 /// Creates a new builder from a string.
@@ -157,15 +145,13 @@ pub fn from_string(string: String) -> BitBuilder {
   do_from_string(string)
 }
 
-if erlang {
-  external fn do_from_string(String) -> BitBuilder =
-    "gleam_stdlib" "wrap_list"
-}
+@target(erlang)
+@external(erlang, "gleam_stdlib", "wrap_list")
+fn do_from_string(a: String) -> BitBuilder
 
-if javascript {
-  fn do_from_string(string: String) -> BitBuilder {
-    Text(string_builder.from_string(string))
-  }
+@target(javascript)
+fn do_from_string(string: String) -> BitBuilder {
+  Text(string_builder.from_string(string))
 }
 
 /// Creates a new builder from a string builder.
@@ -177,15 +163,13 @@ pub fn from_string_builder(builder: StringBuilder) -> BitBuilder {
   do_from_string_builder(builder)
 }
 
-if erlang {
-  external fn do_from_string_builder(StringBuilder) -> BitBuilder =
-    "gleam_stdlib" "wrap_list"
-}
+@target(erlang)
+@external(erlang, "gleam_stdlib", "wrap_list")
+fn do_from_string_builder(a: StringBuilder) -> BitBuilder
 
-if javascript {
-  fn do_from_string_builder(builder: StringBuilder) -> BitBuilder {
-    Text(builder)
-  }
+@target(javascript)
+fn do_from_string_builder(builder: StringBuilder) -> BitBuilder {
+  Text(builder)
 }
 
 /// Creates a new builder from a bit string.
@@ -196,15 +180,13 @@ pub fn from_bit_string(bits: BitString) -> BitBuilder {
   do_from_bit_string(bits)
 }
 
-if erlang {
-  external fn do_from_bit_string(BitString) -> BitBuilder =
-    "gleam_stdlib" "wrap_list"
-}
+@target(erlang)
+@external(erlang, "gleam_stdlib", "wrap_list")
+fn do_from_bit_string(a: BitString) -> BitBuilder
 
-if javascript {
-  fn do_from_bit_string(bits: BitString) -> BitBuilder {
-    Bits(bits)
-  }
+@target(javascript)
+fn do_from_bit_string(bits: BitString) -> BitBuilder {
+  Bits(bits)
 }
 
 /// Turns an builder into a bit string.
@@ -218,39 +200,38 @@ pub fn to_bit_string(builder: BitBuilder) -> BitString {
   do_to_bit_string(builder)
 }
 
-if erlang {
-  external fn do_to_bit_string(BitBuilder) -> BitString =
-    "erlang" "list_to_bitstring"
-}
+@target(erlang)
+@external(erlang, "erlang", "list_to_bitstring")
+fn do_to_bit_string(a: BitBuilder) -> BitString
 
-if javascript {
-  fn do_to_bit_string(builder: BitBuilder) -> BitString {
-    [[builder]]
-    |> to_list([])
-    |> list.reverse
-    |> bit_string.concat
-  }
-
-  fn to_list(
-    stack: List(List(BitBuilder)),
-    acc: List(BitString),
-  ) -> List(BitString) {
-    case stack {
-      [] -> acc
+@target(javascript)
+fn do_to_bit_string(builder: BitBuilder) -> BitString {
+  [[builder]]
+  |> to_list([])
+  |> list.reverse
+  |> bit_string.concat
+}
 
-      [[], ..remaining_stack] -> to_list(remaining_stack, acc)
+@target(javascript)
+fn to_list(
+  stack: List(List(BitBuilder)),
+  acc: List(BitString),
+) -> List(BitString) {
+  case stack {
+    [] -> acc
 
-      [[Bits(bits), ..rest], ..remaining_stack] ->
-        to_list([rest, ..remaining_stack], [bits, ..acc])
+    [[], ..remaining_stack] -> to_list(remaining_stack, acc)
 
-      [[Text(builder), ..rest], ..remaining_stack] -> {
-        let bits = bit_string.from_string(string_builder.to_string(builder))
-        to_list([rest, ..remaining_stack], [bits, ..acc])
-      }
+    [[Bits(bits), ..rest], ..remaining_stack] ->
+      to_list([rest, ..remaining_stack], [bits, ..acc])
 
-      [[Many(builders), ..rest], ..remaining_stack] ->
-        to_list([builders, rest, ..remaining_stack], acc)
+    [[Text(builder), ..rest], ..remaining_stack] -> {
+      let bits = bit_string.from_string(string_builder.to_string(builder))
+      to_list([rest, ..remaining_stack], [bits, ..acc])
     }
+
+    [[Many(builders), ..rest], ..remaining_stack] ->
+      to_list([builders, rest, ..remaining_stack], acc)
   }
 }
 
@@ -262,15 +243,13 @@ pub fn byte_size(builder: BitBuilder) -> Int {
   do_byte_size(builder)
 }
 
-if erlang {
-  external fn do_byte_size(BitBuilder) -> Int =
-    "erlang" "iolist_size"
-}
+@target(erlang)
+@external(erlang, "erlang", "iolist_size")
+fn do_byte_size(a: BitBuilder) -> Int
 
-if javascript {
-  fn do_byte_size(builder: BitBuilder) -> Int {
-    [[builder]]
-    |> to_list([])
-    |> list.fold(0, fn(acc, builder) { bit_string.byte_size(builder) + acc })
-  }
+@target(javascript)
+fn do_byte_size(builder: BitBuilder) -> Int {
+  [[builder]]
+  |> to_list([])
+  |> list.fold(0, fn(acc, builder) { bit_string.byte_size(builder) + acc })
 }
diff --git a/src/gleam/bit_string.gleam b/src/gleam/bit_string.gleam
index 6a67028..25ad686 100644
--- a/src/gleam/bit_string.gleam
+++ b/src/gleam/bit_string.gleam
@@ -8,15 +8,9 @@ pub fn from_string(x: String) -> BitString {
   do_from_string(x)
 }
 
-if erlang {
-  external fn do_from_string(String) -> BitString =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_from_string(String) -> BitString =
-    "../gleam_stdlib.mjs" "bit_string_from_string"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "bit_string_from_string")
+fn do_from_string(a: String) -> BitString
 
 /// Returns an integer which is the number of bytes in the bit string.
 ///
@@ -24,15 +18,9 @@ pub fn byte_size(x: BitString) -> Int {
   do_byte_size(x)
 }
 
-if erlang {
-  external fn do_byte_size(BitString) -> Int =
-    "erlang" "byte_size"
-}
-
-if javascript {
-  external fn do_byte_size(BitString) -> Int =
-    "../gleam_stdlib.mjs" "length"
-}
+@external(erlang, "erlang", "byte_size")
+@external(javascript, "../gleam_stdlib.mjs", "length")
+fn do_byte_size(a: BitString) -> Int
 
 /// Creates a new bit string by joining two binaries.
 ///
@@ -63,23 +51,13 @@ pub fn slice(
   do_slice(string, position, length)
 }
 
-if erlang {
-  external fn do_slice(
-    string: BitString,
-    position: Int,
-    length: Int,
-  ) -> Result(BitString, Nil) =
-    "gleam_stdlib" "bit_string_slice"
-}
-
-if javascript {
-  external fn do_slice(
-    string: BitString,
-    position: Int,
-    length: Int,
-  ) -> Result(BitString, Nil) =
-    "../gleam_stdlib.mjs" "bit_string_slice"
-}
+@external(erlang, "gleam_stdlib", "bit_string_slice")
+@external(javascript, "../gleam_stdlib.mjs", "bit_string_slice")
+fn do_slice(
+  string string: BitString,
+  position position: Int,
+  length length: Int,
+) -> Result(BitString, Nil)
 
 /// Tests to see whether a bit string is valid UTF-8.
 ///
@@ -87,22 +65,20 @@ pub fn is_utf8(bits: BitString) -> Bool {
   do_is_utf8(bits)
 }
 
-if erlang {
-  fn do_is_utf8(bits: BitString) -> Bool {
-    case bits {
-      <<>> -> True
-      <<_:utf8, rest:binary>> -> do_is_utf8(rest)
-      _ -> False
-    }
+@target(erlang)
+fn do_is_utf8(bits: BitString) -> Bool {
+  case bits {
+    <<>> -> True
+    <<_:utf8, rest:binary>> -> do_is_utf8(rest)
+    _ -> False
   }
 }
 
-if javascript {
-  fn do_is_utf8(bits: BitString) -> Bool {
-    case to_string(bits) {
-      Ok(_) -> True
-      _ -> False
-    }
+@target(javascript)
+fn do_is_utf8(bits: BitString) -> Bool {
+  case to_string(bits) {
+    Ok(_) -> True
+    _ -> False
   }
 }
 
@@ -114,22 +90,21 @@ pub fn to_string(bits: BitString) -> Result(String, Nil) {
   do_to_string(bits)
 }
 
-if erlang {
-  external fn unsafe_to_string(BitString) -> String =
-    "gleam_stdlib" "identity"
+@target(erlang)
+@external(erlang, "gleam_stdlib", "identity")
+fn unsafe_to_string(a: BitString) -> String
 
-  fn do_to_string(bits: BitString) -> Result(String, Nil) {
-    case is_utf8(bits) {
-      True -> Ok(unsafe_to_string(bits))
-      False -> Error(Nil)
-    }
+@target(erlang)
+fn do_to_string(bits: BitString) -> Result(String, Nil) {
+  case is_utf8(bits) {
+    True -> Ok(unsafe_to_string(bits))
+    False -> Error(Nil)
   }
 }
 
-if javascript {
-  external fn do_to_string(BitString) -> Result(String, Nil) =
-    "../gleam_stdlib.mjs" "bit_string_to_string"
-}
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "bit_string_to_string")
+fn do_to_string(a: BitString) -> Result(String, Nil)
 
 /// Creates a new bit string by joining multiple binaries.
 ///
@@ -144,12 +119,6 @@ pub fn concat(bit_strings: List(BitString)) -> BitString {
   do_concat(bit_strings)
 }
 
-if erlang {
-  external fn do_concat(List(BitString)) -> BitString =
-    "gleam_stdlib" "bit_string_concat"
-}
-
-if javascript {
-  external fn do_concat(List(BitString)) -> BitString =
-    "../gleam_stdlib.mjs" "bit_string_concat"
-}
+@external(erlang, "gleam_stdlib", "bit_string_concat")
+@external(javascript, "../gleam_stdlib.mjs", "bit_string_concat")
+fn do_concat(a: List(BitString)) -> BitString
diff --git a/src/gleam/dynamic.gleam b/src/gleam/dynamic.gleam
index f6b1717..c48e956 100644
--- a/src/gleam/dynamic.gleam
+++ b/src/gleam/dynamic.gleam
@@ -4,16 +4,14 @@ import gleam/map.{Map}
 import gleam/option.{Option}
 import gleam/result
 import gleam/string_builder
-
-if erlang {
-  import gleam/bit_string
-}
+@target(erlang)
+import gleam/bit_string
 
 /// `Dynamic` data is data that we don't know the type of yet.
 /// We likely get data like this from interop with Erlang, or from
 /// IO with the outside world.
 ///
-pub external type Dynamic
+pub type Dynamic
 
 /// Error returned when unexpected data is encountered
 ///
@@ -33,15 +31,9 @@ pub fn from(a) -> Dynamic {
   do_from(a)
 }
 
-if erlang {
-  external fn do_from(anything) -> Dynamic =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_from(anything) -> Dynamic =
-    "../gleam_stdlib.mjs" "identity"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "identity")
+fn do_from(a: anything) -> Dynamic
 
 /// Unsafely casts a Dynamic value into any other type.
 ///
@@ -54,15 +46,9 @@ pub fn unsafe_coerce(a: Dynamic) -> anything {
   do_unsafe_coerce(a)
 }
 
-if erlang {
-  external fn do_unsafe_coerce(Dynamic) -> a =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_unsafe_coerce(Dynamic) -> a =
-    "../gleam_stdlib.mjs" "identity"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "identity")
+fn do_unsafe_coerce(a: Dynamic) -> a
 
 /// Decodes a `Dynamic` value from a `Dynamic` value.
 ///
@@ -93,15 +79,9 @@ pub fn bit_string(from data: Dynamic) -> Result(BitString, DecodeErrors) {
   decode_bit_string(data)
 }
 
-if erlang {
-  external fn decode_bit_string(Dynamic) -> Result(BitString, DecodeErrors) =
-    "gleam_stdlib" "decode_bit_string"
-}
-
-if javascript {
-  external fn decode_bit_string(Dynamic) -> Result(BitString, DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_bit_string"
-}
+@external(erlang, "gleam_stdlib", "decode_bit_string")
+@external(javascript, "../gleam_stdlib.mjs", "decode_bit_string")
+fn decode_bit_string(a: Dynamic) -> Result(BitString, DecodeErrors)
 
 /// Checks to see whether a `Dynamic` value is a string, and returns that string if
 /// it is.
@@ -129,29 +109,28 @@ fn map_errors(
   result.map_error(result, list.map(_, f))
 }
 
-if erlang {
-  fn decode_string(data: Dynamic) -> Result(String, DecodeErrors) {
-    bit_string(data)
-    |> map_errors(put_expected(_, "String"))
-    |> result.try(fn(raw) {
-      case bit_string.to_string(raw) {
-        Ok(string) -> Ok(string)
-        Error(Nil) ->
-          Error([DecodeError(expected: "String", found: "BitString", path: [])])
-      }
-    })
-  }
-
-  fn put_expected(error: DecodeError, expected: String) -> DecodeError {
-    DecodeError(..error, expected: expected)
-  }
+@target(erlang)
+fn decode_string(data: Dynamic) -> Result(String, DecodeErrors) {
+  bit_string(data)
+  |> map_errors(put_expected(_, "String"))
+  |> result.try(fn(raw) {
+    case bit_string.to_string(raw) {
+      Ok(string) -> Ok(string)
+      Error(Nil) ->
+        Error([DecodeError(expected: "String", found: "BitString", path: [])])
+    }
+  })
 }
 
-if javascript {
-  external fn decode_string(Dynamic) -> Result(String, DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_string"
+@target(erlang)
+fn put_expected(error: DecodeError, expected: String) -> DecodeError {
+  DecodeError(..error, expected: expected)
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "decode_string")
+fn decode_string(a: Dynamic) -> Result(String, DecodeErrors)
+
 /// Return a string indicating the type of the dynamic value.
 ///
 /// ```gleam
@@ -163,15 +142,9 @@ pub fn classify(data: Dynamic) -> String {
   do_classify(data)
 }
 
-if erlang {
-  external fn do_classify(Dynamic) -> String =
-    "gleam_stdlib" "classify_dynamic"
-}
-
-if javascript {
-  external fn do_classify(Dynamic) -> String =
-    "../gleam_stdlib.mjs" "classify_dynamic"
-}
+@external(erlang, "gleam_stdlib", "classify_dynamic")
+@external(javascript, "../gleam_stdlib.mjs", "classify_dynamic")
+fn do_classify(a: Dynamic) -> String
 
 /// Checks to see whether a `Dynamic` value is an int, and returns that int if it
 /// is.
@@ -192,15 +165,9 @@ pub fn int(from data: Dynamic) -> Result(Int, DecodeErrors) {
   decode_int(data)
 }
 
-if erlang {
-  external fn decode_int(Dynamic) -> Result(Int, DecodeErrors) =
-    "gleam_stdlib" "decode_int"
-}
-
-if javascript {
-  external fn decode_int(Dynamic) -> Result(Int, DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_int"
-}
+@external(erlang, "gleam_stdlib", "decode_int")
+@external(javascript, "../gleam_stdlib.mjs", "decode_int")
+fn decode_int(a: Dynamic) -> Result(Int, DecodeErrors)
 
 /// Checks to see whether a `Dynamic` value is a float, and returns that float if
 /// it is.
@@ -221,15 +188,9 @@ pub fn float(from data: Dynamic) -> Result(Float, DecodeErrors) {
   decode_float(data)
 }
 
-if erlang {
-  external fn decode_float(Dynamic) -> Result(Float, DecodeErrors) =
-    "gleam_stdlib" "decode_float"
-}
-
-if javascript {
-  external fn decode_float(Dynamic) -> Result(Float, DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_float"
-}
+@external(erlang, "gleam_stdlib", "decode_float")
+@external(javascript, "../gleam_stdlib.mjs", "decode_float")
+fn decode_float(a: Dynamic) -> Result(Float, DecodeErrors)
 
 /// Checks to see whether a `Dynamic` value is a bool, and returns that bool if
 /// it is.
@@ -250,15 +211,9 @@ pub fn bool(from data: Dynamic) -> Result(Bool, DecodeErrors) {
   decode_bool(data)
 }
 
-if erlang {
-  external fn decode_bool(Dynamic) -> Result(Bool, DecodeErrors) =
-    "gleam_stdlib" "decode_bool"
-}
-
-if javascript {
-  external fn decode_bool(Dynamic) -> Result(Bool, DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_bool"
-}
+@external(erlang, "gleam_stdlib", "decode_bool")
+@external(javascript, "../gleam_stdlib.mjs", "decode_bool")
+fn decode_bool(a: Dynamic) -> Result(Bool, DecodeErrors)
 
 /// Checks to see whether a `Dynamic` value is a list, and returns that list if it
 /// is. The types of the elements are not checked.
@@ -282,25 +237,13 @@ pub fn shallow_list(from value: Dynamic) -> Result(List(Dynamic), DecodeErrors)
   decode_list(value)
 }
 
-if erlang {
-  external fn decode_list(Dynamic) -> Result(List(Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_list"
-}
-
-if javascript {
-  external fn decode_list(Dynamic) -> Result(List(Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_list"
-}
+@external(erlang, "gleam_stdlib", "decode_list")
+@external(javascript, "../gleam_stdlib.mjs", "decode_list")
+fn decode_list(a: Dynamic) -> Result(List(Dynamic), DecodeErrors)
 
-if erlang {
-  external fn decode_result(Dynamic) -> Result(Result(a, e), DecodeErrors) =
-    "gleam_stdlib" "decode_result"
-}
-
-if javascript {
-  external fn decode_result(Dynamic) -> Result(Result(a, e), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_result"
-}
+@external(erlang, "gleam_stdlib", "decode_result")
+@external(javascript, "../gleam_stdlib.mjs", "decode_result")
+fn decode_result(a: Dynamic) -> Result(Result(a, e), DecodeErrors)
 
 /// Checks to see whether a `Dynamic` value is a result of a particular type, and
 /// returns that result if it is.
@@ -440,21 +383,9 @@ pub fn optional(of decode: Decoder(inner)) -> Decoder(Option(inner)) {
   fn(value) { decode_optional(value, decode) }
 }
 
-if erlang {
-  external fn decode_optional(
-    Dynamic,
-    Decoder(a),
-  ) -> Result(Option(a), DecodeErrors) =
-    "gleam_stdlib" "decode_option"
-}
-
-if javascript {
-  external fn decode_optional(
-    Dynamic,
-    Decoder(a),
-  ) -> Result(Option(a), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_option"
-}
+@external(erlang, "gleam_stdlib", "decode_option")
+@external(javascript, "../gleam_stdlib.mjs", "decode_option")
+fn decode_optional(a: Dynamic, b: Decoder(a)) -> Result(Option(a), DecodeErrors)
 
 /// Checks to see if a `Dynamic` value is a map with a specific field, and returns
 /// the value of that field if it is.
@@ -536,21 +467,9 @@ pub fn optional_field(
   }
 }
 
-if erlang {
-  external fn decode_field(
-    Dynamic,
-    name,
-  ) -> Result(Option(Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_field"
-}
-
-if javascript {
-  external fn decode_field(
-    Dynamic,
-    name,
-  ) -> Result(Option(Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_field"
-}
+@external(erlang, "gleam_stdlib", "decode_field")
+@external(javascript, "../gleam_stdlib.mjs", "decode_field")
+fn decode_field(a: Dynamic, b: name) -> Result(Option(Dynamic), DecodeErrors)
 
 /// Checks to see if a `Dynamic` value is a tuple large enough to have a certain
 /// index, and returns the value of that index if it is.
@@ -613,85 +532,50 @@ fn at_least_decode_tuple_error(
 }
 
 // A tuple of unknown size
-external type UnknownTuple
-
-if erlang {
-  external fn decode_tuple(Dynamic) -> Result(UnknownTuple, DecodeErrors) =
-    "gleam_stdlib" "decode_tuple"
-
-  external fn decode_tuple2(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_tuple2"
-
-  external fn decode_tuple3(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic, Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_tuple3"
-
-  external fn decode_tuple4(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic, Dynamic, Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_tuple4"
-
-  external fn decode_tuple5(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic, Dynamic, Dynamic, Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_tuple5"
-
-  external fn decode_tuple6(
-    Dynamic,
-  ) -> Result(
-    #(Dynamic, Dynamic, Dynamic, Dynamic, Dynamic, Dynamic),
-    DecodeErrors,
-  ) =
-    "gleam_stdlib" "decode_tuple6"
-
-  external fn tuple_get(UnknownTuple, Int) -> Result(Dynamic, DecodeErrors) =
-    "gleam_stdlib" "tuple_get"
-
-  external fn tuple_size(UnknownTuple) -> Int =
-    "gleam_stdlib" "size_of_tuple"
-}
-
-if javascript {
-  external fn decode_tuple(Dynamic) -> Result(UnknownTuple, DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_tuple"
-
-  external fn decode_tuple2(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_tuple2"
-
-  external fn decode_tuple3(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic, Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_tuple3"
-
-  external fn decode_tuple4(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic, Dynamic, Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_tuple4"
-
-  external fn decode_tuple5(
-    Dynamic,
-  ) -> Result(#(Dynamic, Dynamic, Dynamic, Dynamic, Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_tuple5"
-
-  external fn decode_tuple6(
-    Dynamic,
-  ) -> Result(
-    #(Dynamic, Dynamic, Dynamic, Dynamic, Dynamic, Dynamic),
-    DecodeErrors,
-  ) =
-    "../gleam_stdlib.mjs" "decode_tuple6"
-
-  external fn tuple_get(UnknownTuple, Int) -> Result(Dynamic, DecodeErrors) =
-    "../gleam_stdlib.mjs" "tuple_get"
-
-  external fn tuple_size(UnknownTuple) -> Int =
-    "../gleam_stdlib.mjs" "length"
-}
+type UnknownTuple
+
+@external(erlang, "gleam_stdlib", "decode_tuple")
+@external(javascript, "../gleam_stdlib.mjs", "decode_tuple")
+fn decode_tuple(a: Dynamic) -> Result(UnknownTuple, DecodeErrors)
+
+@external(erlang, "gleam_stdlib", "decode_tuple2")
+@external(javascript, "../gleam_stdlib.mjs", "decode_tuple2")
+fn decode_tuple2(a: Dynamic) -> Result(#(Dynamic, Dynamic), DecodeErrors)
+
+@external(erlang, "gleam_stdlib", "decode_tuple3")
+@external(javascript, "../gleam_stdlib.mjs", "decode_tuple3")
+fn decode_tuple3(
+  a: Dynamic,
+) -> Result(#(Dynamic, Dynamic, Dynamic), DecodeErrors)
+
+@external(erlang, "gleam_stdlib", "decode_tuple4")
+@external(javascript, "../gleam_stdlib.mjs", "decode_tuple4")
+fn decode_tuple4(
+  a: Dynamic,
+) -> Result(#(Dynamic, Dynamic, Dynamic, Dynamic), DecodeErrors)
+
+@external(erlang, "gleam_stdlib", "decode_tuple5")
+@external(javascript, "../gleam_stdlib.mjs", "decode_tuple5")
+fn decode_tuple5(
+  a: Dynamic,
+) -> Result(#(Dynamic, Dynamic, Dynamic, Dynamic, Dynamic), DecodeErrors)
+
+@external(erlang, "gleam_stdlib", "decode_tuple6")
+@external(javascript, "../gleam_stdlib.mjs", "decode_tuple6")
+fn decode_tuple6(
+  a: Dynamic,
+) -> Result(
+  #(Dynamic, Dynamic, Dynamic, Dynamic, Dynamic, Dynamic),
+  DecodeErrors,
+)
+
+@external(erlang, "gleam_stdlib", "tuple_get")
+@external(javascript, "../gleam_stdlib.mjs", "tuple_get")
+fn tuple_get(a: UnknownTuple, b: Int) -> Result(Dynamic, DecodeErrors)
+
+@external(erlang, "gleam_stdlib", "size_of_tuple")
+@external(javascript, "../gleam_stdlib.mjs", "length")
+fn tuple_size(a: UnknownTuple) -> Int
 
 fn tuple_errors(
   result: Result(a, List(DecodeError)),
@@ -1084,15 +968,9 @@ pub fn map(
   }
 }
 
-if erlang {
-  external fn decode_map(Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeErrors) =
-    "gleam_stdlib" "decode_map"
-}
-
-if javascript {
-  external fn decode_map(Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeErrors) =
-    "../gleam_stdlib.mjs" "decode_map"
-}
+@external(erlang, "gleam_stdlib", "decode_map")
+@external(javascript, "../gleam_stdlib.mjs", "decode_map")
+fn decode_map(a: Dynamic) -> Result(Map(Dynamic, Dynamic), DecodeErrors)
 
 /// Joins multiple decoders into one. When run they will each be tried in turn
 /// until one succeeds, or they all fail.
diff --git a/src/gleam/float.gleam b/src/gleam/float.gleam
index 1ee175c..a70a2e9 100644
--- a/src/gleam/float.gleam
+++ b/src/gleam/float.gleam
@@ -19,15 +19,9 @@ pub fn parse(string: String) -> Result(Float, Nil) {
   do_parse(string)
 }
 
-if erlang {
-  external fn do_parse(String) -> Result(Float, Nil) =
-    "gleam_stdlib" "parse_float"
-}
-
-if javascript {
-  external fn do_parse(String) -> Result(Float, Nil) =
-    "../gleam_stdlib.mjs" "parse_float"
-}
+@external(erlang, "gleam_stdlib", "parse_float")
+@external(javascript, "../gleam_stdlib.mjs", "parse_float")
+fn do_parse(a: String) -> Result(Float, Nil)
 
 /// Returns the string representation of the provided `Float`.
 ///
@@ -42,15 +36,9 @@ pub fn to_string(x: Float) -> String {
   do_to_string(x)
 }
 
-if erlang {
-  external fn do_to_string(Float) -> String =
-    "gleam_stdlib" "float_to_string"
-}
-
-if javascript {
-  external fn do_to_string(Float) -> String =
-    "../gleam_stdlib.mjs" "float_to_string"
-}
+@external(erlang, "gleam_stdlib", "float_to_string")
+@external(javascript, "../gleam_stdlib.mjs", "float_to_string")
+fn do_to_string(a: Float) -> String
 
 /// Restricts a `Float` between a lower and upper bound.
 ///
@@ -198,15 +186,9 @@ pub fn ceiling(x: Float) -> Float {
   do_ceiling(x)
 }
 
-if erlang {
-  external fn do_ceiling(Float) -> Float =
-    "math" "ceil"
-}
-
-if javascript {
-  external fn do_ceiling(Float) -> Float =
-    "../gleam_stdlib.mjs" "ceiling"
-}
+@external(erlang, "math", "ceil")
+@external(javascript, "../gleam_stdlib.mjs", "ceiling")
+fn do_ceiling(a: Float) -> Float
 
 /// Rounds the value to the next lowest whole number as a `Float`.
 ///
@@ -221,15 +203,9 @@ pub fn floor(x: Float) -> Float {
   do_floor(x)
 }
 
-if erlang {
-  external fn do_floor(Float) -> Float =
-    "math" "floor"
-}
-
-if javascript {
-  external fn do_floor(Float) -> Float =
-    "../gleam_stdlib.mjs" "floor"
-}
+@external(erlang, "math", "floor")
+@external(javascript, "../gleam_stdlib.mjs", "floor")
+fn do_floor(a: Float) -> Float
 
 /// Rounds the value to the nearest whole number as an `Int`.
 ///
@@ -249,23 +225,22 @@ pub fn round(x: Float) -> Int {
   do_round(x)
 }
 
-if erlang {
-  external fn do_round(Float) -> Int =
-    "erlang" "round"
-}
+@target(erlang)
+@external(erlang, "erlang", "round")
+fn do_round(a: Float) -> Int
 
-if javascript {
-  fn do_round(x: Float) -> Int {
-    case x >=. 0.0 {
-      True -> js_round(x)
-      _ -> 0 - js_round(negate(x))
-    }
+@target(javascript)
+fn do_round(x: Float) -> Int {
+  case x >=. 0.0 {
+    True -> js_round(x)
+    _ -> 0 - js_round(negate(x))
   }
-
-  external fn js_round(Float) -> Int =
-    "../gleam_stdlib.mjs" "round"
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "round")
+fn js_round(a: Float) -> Int
+
 /// Returns the value as an `Int`, truncating all decimal digits.
 ///
 /// ## Examples
@@ -279,15 +254,9 @@ pub fn truncate(x: Float) -> Int {
   do_truncate(x)
 }
 
-if erlang {
-  external fn do_truncate(Float) -> Int =
-    "erlang" "trunc"
-}
-
-if javascript {
-  external fn do_truncate(Float) -> Int =
-    "../gleam_stdlib.mjs" "truncate"
-}
+@external(erlang, "erlang", "trunc")
+@external(javascript, "../gleam_stdlib.mjs", "truncate")
+fn do_truncate(a: Float) -> Int
 
 /// Returns the absolute value of the input as a `Float`.
 ///
@@ -354,15 +323,9 @@ pub fn power(base: Float, of exponent: Float) -> Result(Float, Nil) {
   }
 }
 
-if erlang {
-  external fn do_power(Float, Float) -> Float =
-    "math" "pow"
-}
-
-if javascript {
-  external fn do_power(Float, Float) -> Float =
-    "../gleam_stdlib.mjs" "power"
-}
+@external(erlang, "math", "pow")
+@external(javascript, "../gleam_stdlib.mjs", "power")
+fn do_power(a: Float, b: Float) -> Float
 
 /// Returns the square root of the input as a `Float`.
 ///
@@ -467,19 +430,13 @@ pub fn random(boundary_a: Float, boundary_b: Float) -> Float {
   }
 }
 
-if erlang {
-  /// Returns a random float uniformly distributed in the value range
-  /// 0.0 =< X < 1.0 and updates the state in the process dictionary.
-  /// See: <https://www.erlang.org/doc/man/rand.html#uniform-0>
-  ///
-  external fn do_random_uniform() -> Float =
-    "rand" "uniform"
-}
-
-if javascript {
-  external fn do_random_uniform() -> Float =
-    "../gleam_stdlib.mjs" "random_uniform"
-}
+/// Returns a random float uniformly distributed in the value range
+/// 0.0 =< X < 1.0 and updates the state in the process dictionary.
+/// See: <https://www.erlang.org/doc/man/rand.html#uniform-0>
+///
+@external(erlang, "rand", "uniform")
+@external(javascript, "../gleam_stdlib.mjs", "random_uniform")
+fn do_random_uniform() -> Float
 
 /// Returns division of the inputs as a `Result`.
 ///
diff --git a/src/gleam/int.gleam b/src/gleam/int.gleam
index 793a85e..c49df37 100644
--- a/src/gleam/int.gleam
+++ b/src/gleam/int.gleam
@@ -96,15 +96,9 @@ pub fn parse(string: String) -> Result(Int, Nil) {
   do_parse(string)
 }
 
-if erlang {
-  external fn do_parse(String) -> Result(Int, Nil) =
-    "gleam_stdlib" "parse_int"
-}
-
-if javascript {
-  external fn do_parse(String) -> Result(Int, Nil) =
-    "../gleam_stdlib.mjs" "parse_int"
-}
+@external(erlang, "gleam_stdlib", "parse_int")
+@external(javascript, "../gleam_stdlib.mjs", "parse_int")
+fn do_parse(a: String) -> Result(Int, Nil)
 
 /// Parses a given string as an int in a given base if possible.
 /// Supports only bases 2 to 36, for values outside of which this function returns an `Error(Nil)`.
@@ -135,15 +129,9 @@ pub fn base_parse(string: String, base: Int) -> Result(Int, Nil) {
   }
 }
 
-if erlang {
-  external fn do_base_parse(String, Int) -> Result(Int, Nil) =
-    "gleam_stdlib" "int_from_base_string"
-}
-
-if javascript {
-  external fn do_base_parse(String, Int) -> Result(Int, Nil) =
-    "../gleam_stdlib.mjs" "int_from_base_string"
-}
+@external(erlang, "gleam_stdlib", "int_from_base_string")
+@external(javascript, "../gleam_stdlib.mjs", "int_from_base_string")
+fn do_base_parse(a: String, b: Int) -> Result(Int, Nil)
 
 /// Prints a given int to a string.
 ///
@@ -158,15 +146,9 @@ pub fn to_string(x: Int) {
   do_to_string(x)
 }
 
-if erlang {
-  external fn do_to_string(Int) -> String =
-    "erlang" "integer_to_binary"
-}
-
-if javascript {
-  external fn do_to_string(Int) -> String =
-    "../gleam_stdlib.mjs" "to_string"
-}
+@external(erlang, "erlang", "integer_to_binary")
+@external(javascript, "../gleam_stdlib.mjs", "to_string")
+fn do_to_string(a: Int) -> String
 
 /// Error value when trying to operate with a base out of the allowed range.
 ///
@@ -212,15 +194,9 @@ pub fn to_base_string(x: Int, base: Int) -> Result(String, InvalidBase) {
   }
 }
 
-if erlang {
-  external fn do_to_base_string(Int, Int) -> String =
-    "erlang" "integer_to_binary"
-}
-
-if javascript {
-  external fn do_to_base_string(Int, Int) -> String =
-    "../gleam_stdlib.mjs" "int_to_base_string"
-}
+@external(erlang, "erlang", "integer_to_binary")
+@external(javascript, "../gleam_stdlib.mjs", "int_to_base_string")
+fn do_to_base_string(a: Int, b: Int) -> String
 
 /// Prints a given int to a string using base-2.
 ///
@@ -297,15 +273,9 @@ pub fn to_float(x: Int) -> Float {
   do_to_float(x)
 }
 
-if erlang {
-  external fn do_to_float(Int) -> Float =
-    "erlang" "float"
-}
-
-if javascript {
-  external fn do_to_float(Int) -> Float =
-    "../gleam_stdlib.mjs" "identity"
-}
+@external(erlang, "erlang", "float")
+@external(javascript, "../gleam_stdlib.mjs", "identity")
+fn do_to_float(a: Int) -> Float
 
 /// Restricts an int between a lower and upper bound.
 ///
diff --git a/src/gleam/io.gleam b/src/gleam/io.gleam
index c8524f1..0c0a3ee 100644
--- a/src/gleam/io.gleam
+++ b/src/gleam/io.gleam
@@ -16,15 +16,9 @@ pub fn print(string: String) -> Nil {
   do_print(string)
 }
 
-if erlang {
-  external fn do_print(string: String) -> Nil =
-    "gleam_stdlib" "print"
-}
-
-if javascript {
-  external fn do_print(String) -> Nil =
-    "../gleam_stdlib.mjs" "print"
-}
+@external(erlang, "gleam_stdlib", "print")
+@external(javascript, "../gleam_stdlib.mjs", "print")
+fn do_print(string string: String) -> Nil
 
 /// Writes a string to standard error.
 ///
@@ -42,15 +36,9 @@ pub fn print_error(string: String) -> Nil {
   do_print_error(string)
 }
 
-if erlang {
-  external fn do_print_error(string: String) -> Nil =
-    "gleam_stdlib" "print_error"
-}
-
-if javascript {
-  external fn do_print_error(String) -> Nil =
-    "../gleam_stdlib.mjs" "print_error"
-}
+@external(erlang, "gleam_stdlib", "print_error")
+@external(javascript, "../gleam_stdlib.mjs", "print_error")
+fn do_print_error(string string: String) -> Nil
 
 /// Writes a string to standard output, appending a newline to the end.
 ///
@@ -66,15 +54,9 @@ pub fn println(string: String) -> Nil {
   do_println(string)
 }
 
-if erlang {
-  external fn do_println(string: String) -> Nil =
-    "gleam_stdlib" "println"
-}
-
-if javascript {
-  external fn do_println(String) -> Nil =
-    "../gleam_stdlib.mjs" "console_log"
-}
+@external(erlang, "gleam_stdlib", "println")
+@external(javascript, "../gleam_stdlib.mjs", "console_log")
+fn do_println(string string: String) -> Nil
 
 /// Writes a string to standard error, appending a newline to the end.
 ///
@@ -90,15 +72,9 @@ pub fn println_error(string: String) -> Nil {
   do_println_error(string)
 }
 
-if erlang {
-  external fn do_println_error(string: String) -> Nil =
-    "gleam_stdlib" "println_error"
-}
-
-if javascript {
-  external fn do_println_error(String) -> Nil =
-    "../gleam_stdlib.mjs" "console_error"
-}
+@external(erlang, "gleam_stdlib", "println_error")
+@external(javascript, "../gleam_stdlib.mjs", "console_error")
+fn do_println_error(string string: String) -> Nil
 
 /// Prints a value to standard error (stderr) yielding Gleam syntax.
 ///
@@ -136,12 +112,6 @@ pub fn debug(term: anything) -> anything {
   term
 }
 
-if erlang {
-  external fn do_debug_println(string: String) -> Nil =
-    "gleam_stdlib" "println_error"
-}
-
-if javascript {
-  external fn do_debug_println(String) -> Nil =
-    "../gleam_stdlib.mjs" "print_debug"
-}
+@external(erlang, "gleam_stdlib", "println_error")
+@external(javascript, "../gleam_stdlib.mjs", "print_debug")
+fn do_debug_println(string string: String) -> Nil
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index b5bc6f5..e63ecd2 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -63,21 +63,20 @@ pub fn length(of list: List(a)) -> Int {
   do_length(list)
 }
 
-if erlang {
-  external fn do_length(List(a)) -> Int =
-    "erlang" "length"
-}
+@target(erlang)
+@external(erlang, "erlang", "length")
+fn do_length(a: List(a)) -> Int
 
-if javascript {
-  fn do_length(list: List(a)) -> Int {
-    do_length_acc(list, 0)
-  }
+@target(javascript)
+fn do_length(list: List(a)) -> Int {
+  do_length_acc(list, 0)
+}
 
-  fn do_length_acc(list: List(a), count: Int) -> Int {
-    case list {
-      [_, ..list] -> do_length_acc(list, count + 1)
-      _ -> count
-    }
+@target(javascript)
+fn do_length_acc(list: List(a), count: Int) -> Int {
+  case list {
+    [_, ..list] -> do_length_acc(list, count + 1)
+    _ -> count
   }
 }
 
@@ -111,21 +110,20 @@ pub fn reverse(xs: List(a)) -> List(a) {
   do_reverse(xs)
 }
 
-if erlang {
-  external fn do_reverse(List(a)) -> List(a) =
-    "lists" "reverse"
-}
+@target(erlang)
+@external(erlang, "lists", "reverse")
+fn do_reverse(a: List(a)) -> List(a)
 
-if javascript {
-  fn do_reverse(list) {
-    do_reverse_acc(list, [])
-  }
+@target(javascript)
+fn do_reverse(list) {
+  do_reverse_acc(list, [])
+}
 
-  fn do_reverse_acc(remaining, accumulator) {
-    case remaining {
-      [] -> accumulator
-      [item, ..rest] -> do_reverse_acc(rest, [item, ..accumulator])
-    }
+@target(javascript)
+fn do_reverse_acc(remaining, accumulator) {
+  case remaining {
+    [] -> accumulator
+    [item, ..rest] -> do_reverse_acc(rest, [item, ..accumulator])
   }
 }
 
@@ -623,21 +621,20 @@ pub fn append(first: List(a), second: List(a)) -> List(a) {
   do_append(first, second)
 }
 
-if erlang {
-  external fn do_append(List(a), List(a)) -> List(a) =
-    "lists" "append"
-}
+@target(erlang)
+@external(erlang, "lists", "append")
+fn do_append(a: List(a), b: List(a)) -> List(a)
 
-if javascript {
-  fn do_append(first: List(a), second: List(a)) -> List(a) {
-    do_append_acc(reverse(first), second)
-  }
+@target(javascript)
+fn do_append(first: List(a), second: List(a)) -> List(a) {
+  do_append_acc(reverse(first), second)
+}
 
-  fn do_append_acc(first: List(a), second: List(a)) -> List(a) {
-    case first {
-      [] -> second
-      [item, ..rest] -> do_append_acc(rest, [item, ..second])
-    }
+@target(javascript)
+fn do_append_acc(first: List(a), second: List(a)) -> List(a) {
+  case first {
+    [] -> second
+    [item, ..rest] -> do_append_acc(rest, [item, ..second])
   }
 }
 
diff --git a/src/gleam/map.gleam b/src/gleam/map.gleam
index 6f963bc..07d9234 100644
--- a/src/gleam/map.gleam
+++ b/src/gleam/map.gleam
@@ -14,7 +14,7 @@ import gleam/option.{Option}
 /// See [the Erlang map module](https://erlang.org/doc/man/maps.html) for more
 /// information.
 ///
-pub external type Map(key, value)
+pub type Map(key, value)
 
 /// Determines the number of key-value pairs in the map.
 /// This function runs in constant time and does not need to iterate the map.
@@ -35,15 +35,9 @@ pub fn size(map: Map(k, v)) -> Int {
   do_size(map)
 }
 
-if erlang {
-  external fn do_size(Map(k, v)) -> Int =
-    "maps" "size"
-}
-
-if javascript {
-  external fn do_size(Map(k, v)) -> Int =
-    "../gleam_stdlib.mjs" "map_size"
-}
+@external(erlang, "maps", "size")
+@external(javascript, "../gleam_stdlib.mjs", "map_size")
+fn do_size(a: Map(k, v)) -> Int
 
 /// Converts the map to a list of 2-element tuples `#(key, value)`, one for
 /// each key-value pair in the map.
@@ -66,15 +60,9 @@ pub fn to_list(map: Map(key, value)) -> List(#(key, value)) {
   do_to_list(map)
 }
 
-if erlang {
-  external fn do_to_list(Map(key, value)) -> List(#(key, value)) =
-    "maps" "to_list"
-}
-
-if javascript {
-  external fn do_to_list(Map(key, value)) -> List(#(key, value)) =
-    "../gleam_stdlib.mjs" "map_to_list"
-}
+@external(erlang, "maps", "to_list")
+@external(javascript, "../gleam_stdlib.mjs", "map_to_list")
+fn do_to_list(a: Map(key, value)) -> List(#(key, value))
 
 /// Converts a list of 2-element tuples `#(key, value)` to a map.
 ///
@@ -85,25 +73,24 @@ pub fn from_list(list: List(#(k, v))) -> Map(k, v) {
   do_from_list(list)
 }
 
-if erlang {
-  external fn do_from_list(List(#(key, value))) -> Map(key, value) =
-    "maps" "from_list"
-}
+@target(erlang)
+@external(erlang, "maps", "from_list")
+fn do_from_list(a: List(#(key, value))) -> Map(key, value)
 
-if javascript {
-  fn fold_list_of_pair(
-    over list: List(#(k, v)),
-    from initial: Map(k, v),
-  ) -> Map(k, v) {
-    case list {
-      [] -> initial
-      [x, ..rest] -> fold_list_of_pair(rest, insert(initial, x.0, x.1))
-    }
+@target(javascript)
+fn fold_list_of_pair(
+  over list: List(#(k, v)),
+  from initial: Map(k, v),
+) -> Map(k, v) {
+  case list {
+    [] -> initial
+    [x, ..rest] -> fold_list_of_pair(rest, insert(initial, x.0, x.1))
   }
+}
 
-  fn do_from_list(list: List(#(k, v))) -> Map(k, v) {
-    fold_list_of_pair(list, new())
-  }
+@target(javascript)
+fn do_from_list(list: List(#(k, v))) -> Map(k, v) {
+  fold_list_of_pair(list, new())
 }
 
 /// Determines whether or not a value present in the map for a given key.
@@ -124,15 +111,13 @@ pub fn has_key(map: Map(k, v), key: k) -> Bool {
   do_has_key(key, map)
 }
 
-if erlang {
-  external fn do_has_key(key, Map(key, v)) -> Bool =
-    "maps" "is_key"
-}
+@target(erlang)
+@external(erlang, "maps", "is_key")
+fn do_has_key(a: key, b: Map(key, v)) -> Bool
 
-if javascript {
-  fn do_has_key(key: k, map: Map(k, v)) -> Bool {
-    get(map, key) != Error(Nil)
-  }
+@target(javascript)
+fn do_has_key(key: k, map: Map(k, v)) -> Bool {
+  get(map, key) != Error(Nil)
 }
 
 /// Creates a fresh map that contains no values.
@@ -141,15 +126,9 @@ pub fn new() -> Map(key, value) {
   do_new()
 }
 
-if erlang {
-  external fn do_new() -> Map(key, value) =
-    "maps" "new"
-}
-
-if javascript {
-  external fn do_new() -> Map(key, value) =
-    "../gleam_stdlib.mjs" "new_map"
-}
+@external(erlang, "maps", "new")
+@external(javascript, "../gleam_stdlib.mjs", "new_map")
+fn do_new() -> Map(key, value)
 
 /// Fetches a value from a map for a given key.
 ///
@@ -172,15 +151,9 @@ pub fn get(from: Map(key, value), get: key) -> Result(value, Nil) {
   do_get(from, get)
 }
 
-if erlang {
-  external fn do_get(Map(key, value), key) -> Result(value, Nil) =
-    "gleam_stdlib" "map_get"
-}
-
-if javascript {
-  external fn do_get(Map(key, value), key) -> Result(value, Nil) =
-    "../gleam_stdlib.mjs" "map_get"
-}
+@external(erlang, "gleam_stdlib", "map_get")
+@external(javascript, "../gleam_stdlib.mjs", "map_get")
+fn do_get(a: Map(key, value), b: key) -> Result(value, Nil)
 
 /// Inserts a value into the map with the given key.
 ///
@@ -203,15 +176,9 @@ pub fn insert(into map: Map(k, v), for key: k, insert value: v) -> Map(k, v) {
   do_insert(key, value, map)
 }
 
-if erlang {
-  external fn do_insert(key, value, Map(key, value)) -> Map(key, value) =
-    "maps" "put"
-}
-
-if javascript {
-  external fn do_insert(key, value, Map(key, value)) -> Map(key, value) =
-    "../gleam_stdlib.mjs" "map_insert"
-}
+@external(erlang, "maps", "put")
+@external(javascript, "../gleam_stdlib.mjs", "map_insert")
+fn do_insert(a: key, b: value, c: Map(key, value)) -> Map(key, value)
 
 /// Updates all values in a given map by calling a given function on each key
 /// and value.
@@ -229,17 +196,15 @@ pub fn map_values(in map: Map(k, v), with fun: fn(k, v) -> w) -> Map(k, w) {
   do_map_values(fun, map)
 }
 
-if erlang {
-  external fn do_map_values(fn(key, value) -> b, Map(key, value)) -> Map(key, b) =
-    "maps" "map"
-}
+@target(erlang)
+@external(erlang, "maps", "map")
+fn do_map_values(a: fn(key, value) -> b, b: Map(key, value)) -> Map(key, b)
 
-if javascript {
-  fn do_map_values(f: fn(key, value) -> b, map: Map(key, value)) -> Map(key, b) {
-    let f = fn(map, k, v) { insert(map, k, f(k, v)) }
-    map
-    |> fold(from: new(), with: f)
-  }
+@target(javascript)
+fn do_map_values(f: fn(key, value) -> b, map: Map(key, value)) -> Map(key, b) {
+  let f = fn(map, k, v) { insert(map, k, f(k, v)) }
+  map
+  |> fold(from: new(), with: f)
 }
 
 /// Gets a list of all keys in a given map.
@@ -259,32 +224,32 @@ pub fn keys(map: Map(keys, v)) -> List(keys) {
   do_keys(map)
 }
 
-if erlang {
-  external fn do_keys(Map(keys, v)) -> List(keys) =
-    "maps" "keys"
-}
+@target(erlang)
+@external(erlang, "maps", "keys")
+fn do_keys(a: Map(keys, v)) -> List(keys)
 
-if javascript {
-  fn reverse_and_concat(remaining, accumulator) {
-    case remaining {
-      [] -> accumulator
-      [item, ..rest] -> reverse_and_concat(rest, [item, ..accumulator])
-    }
+@target(javascript)
+fn reverse_and_concat(remaining, accumulator) {
+  case remaining {
+    [] -> accumulator
+    [item, ..rest] -> reverse_and_concat(rest, [item, ..accumulator])
   }
+}
 
-  fn do_keys_acc(list: List(#(k, v)), acc: List(k)) -> List(k) {
-    case list {
-      [] -> reverse_and_concat(acc, [])
-      [x, ..xs] -> do_keys_acc(xs, [x.0, ..acc])
-    }
+@target(javascript)
+fn do_keys_acc(list: List(#(k, v)), acc: List(k)) -> List(k) {
+  case list {
+    [] -> reverse_and_concat(acc, [])
+    [x, ..xs] -> do_keys_acc(xs, [x.0, ..acc])
   }
+}
 
-  fn do_keys(map: Map(k, v)) -> List(k) {
-    let list_of_pairs =
-      map
-      |> to_list
-    do_keys_acc(list_of_pairs, [])
-  }
+@target(javascript)
+fn do_keys(map: Map(k, v)) -> List(k) {
+  let list_of_pairs =
+    map
+    |> to_list
+  do_keys_acc(list_of_pairs, [])
 }
 
 /// Gets a list of all values in a given map.
@@ -304,25 +269,24 @@ pub fn values(map: Map(k, values)) -> List(values) {
   do_values(map)
 }
 
-if erlang {
-  external fn do_values(Map(k, values)) -> List(values) =
-    "maps" "values"
-}
+@target(erlang)
+@external(erlang, "maps", "values")
+fn do_values(a: Map(k, values)) -> List(values)
 
-if javascript {
-  fn do_values_acc(list: List(#(k, v)), acc: List(v)) -> List(v) {
-    case list {
-      [] -> reverse_and_concat(acc, [])
-      [x, ..xs] -> do_values_acc(xs, [x.1, ..acc])
-    }
+@target(javascript)
+fn do_values_acc(list: List(#(k, v)), acc: List(v)) -> List(v) {
+  case list {
+    [] -> reverse_and_concat(acc, [])
+    [x, ..xs] -> do_values_acc(xs, [x.1, ..acc])
   }
+}
 
-  fn do_values(map: Map(k, v)) -> List(v) {
-    let list_of_pairs =
-      map
-      |> to_list
-    do_values_acc(list_of_pairs, [])
-  }
+@target(javascript)
+fn do_values(map: Map(k, v)) -> List(v) {
+  let list_of_pairs =
+    map
+    |> to_list
+  do_values_acc(list_of_pairs, [])
 }
 
 /// Creates a new map from a given map, minus any entries that a given function
@@ -346,28 +310,20 @@ pub fn filter(in map: Map(k, v), for property: fn(k, v) -> Bool) -> Map(k, v) {
   do_filter(property, map)
 }
 
-if erlang {
-  external fn do_filter(
-    fn(key, value) -> Bool,
-    Map(key, value),
-  ) -> Map(key, value) =
-    "maps" "filter"
-}
-
-if javascript {
-  fn do_filter(
-    f: fn(key, value) -> Bool,
-    map: Map(key, value),
-  ) -> Map(key, value) {
-    let insert = fn(map, k, v) {
-      case f(k, v) {
-        True -> insert(map, k, v)
-        _ -> map
-      }
+@target(erlang)
+@external(erlang, "maps", "filter")
+fn do_filter(a: fn(key, value) -> Bool, b: Map(key, value)) -> Map(key, value)
+
+@target(javascript)
+fn do_filter(f: fn(key, value) -> Bool, map: Map(key, value)) -> Map(key, value) {
+  let insert = fn(map, k, v) {
+    case f(k, v) {
+      True -> insert(map, k, v)
+      _ -> map
     }
-    map
-    |> fold(from: new(), with: insert)
   }
+  map
+  |> fold(from: new(), with: insert)
 }
 
 /// Creates a new map from a given map, only including any entries for which the
@@ -391,34 +347,33 @@ pub fn take(from map: Map(k, v), keeping desired_keys: List(k)) -> Map(k, v) {
   do_take(desired_keys, map)
 }
 
-if erlang {
-  external fn do_take(List(k), Map(k, v)) -> Map(k, v) =
-    "maps" "with"
-}
+@target(erlang)
+@external(erlang, "maps", "with")
+fn do_take(a: List(k), b: Map(k, v)) -> Map(k, v)
 
-if javascript {
-  fn insert_taken(
-    map: Map(k, v),
-    desired_keys: List(k),
-    acc: Map(k, v),
-  ) -> Map(k, v) {
-    let insert = fn(taken, key) {
-      case get(map, key) {
-        Ok(value) -> insert(taken, key, value)
-        _ -> taken
-      }
-    }
-    case desired_keys {
-      [] -> acc
-      [x, ..xs] -> insert_taken(map, xs, insert(acc, x))
+@target(javascript)
+fn insert_taken(
+  map: Map(k, v),
+  desired_keys: List(k),
+  acc: Map(k, v),
+) -> Map(k, v) {
+  let insert = fn(taken, key) {
+    case get(map, key) {
+      Ok(value) -> insert(taken, key, value)
+      _ -> taken
     }
   }
-
-  fn do_take(desired_keys: List(k), map: Map(k, v)) -> Map(k, v) {
-    insert_taken(map, desired_keys, new())
+  case desired_keys {
+    [] -> acc
+    [x, ..xs] -> insert_taken(map, xs, insert(acc, x))
   }
 }
 
+@target(javascript)
+fn do_take(desired_keys: List(k), map: Map(k, v)) -> Map(k, v) {
+  insert_taken(map, desired_keys, new())
+}
+
 /// Creates a new map from a pair of given maps by combining their entries.
 ///
 /// If there are entries with the same keys in both maps the entry from the
@@ -437,28 +392,28 @@ pub fn merge(into map: Map(k, v), from new_entries: Map(k, v)) -> Map(k, v) {
   do_merge(map, new_entries)
 }
 
-if erlang {
-  external fn do_merge(Map(k, v), Map(k, v)) -> Map(k, v) =
-    "maps" "merge"
-}
+@target(erlang)
+@external(erlang, "maps", "merge")
+fn do_merge(a: Map(k, v), b: Map(k, v)) -> Map(k, v)
 
-if javascript {
-  fn insert_pair(map: Map(k, v), pair: #(k, v)) -> Map(k, v) {
-    insert(map, pair.0, pair.1)
-  }
+@target(javascript)
+fn insert_pair(map: Map(k, v), pair: #(k, v)) -> Map(k, v) {
+  insert(map, pair.0, pair.1)
+}
 
-  fn fold_inserts(new_entries: List(#(k, v)), map: Map(k, v)) -> Map(k, v) {
-    case new_entries {
-      [] -> map
-      [x, ..xs] -> fold_inserts(xs, insert_pair(map, x))
-    }
+@target(javascript)
+fn fold_inserts(new_entries: List(#(k, v)), map: Map(k, v)) -> Map(k, v) {
+  case new_entries {
+    [] -> map
+    [x, ..xs] -> fold_inserts(xs, insert_pair(map, x))
   }
+}
 
-  fn do_merge(map: Map(k, v), new_entries: Map(k, v)) -> Map(k, v) {
-    new_entries
-    |> to_list
-    |> fold_inserts(map)
-  }
+@target(javascript)
+fn do_merge(map: Map(k, v), new_entries: Map(k, v)) -> Map(k, v) {
+  new_entries
+  |> to_list
+  |> fold_inserts(map)
 }
 
 /// Creates a new map from a given map with all the same entries except for the
@@ -480,15 +435,9 @@ pub fn delete(from map: Map(k, v), delete key: k) -> Map(k, v) {
   do_delete(key, map)
 }
 
-if erlang {
-  external fn do_delete(k, Map(k, v)) -> Map(k, v) =
-    "maps" "remove"
-}
-
-if javascript {
-  external fn do_delete(k, Map(k, v)) -> Map(k, v) =
-    "../gleam_stdlib.mjs" "map_remove"
-}
+@external(erlang, "maps", "remove")
+@external(javascript, "../gleam_stdlib.mjs", "map_remove")
+fn do_delete(a: k, b: Map(k, v)) -> Map(k, v)
 
 /// Creates a new map from a given map with all the same entries except any with
 /// keys found in a given list.
diff --git a/src/gleam/regex.gleam b/src/gleam/regex.gleam
index f1161cc..10b09e2 100644
--- a/src/gleam/regex.gleam
+++ b/src/gleam/regex.gleam
@@ -5,7 +5,7 @@
 
 import gleam/option.{Option}
 
-pub external type Regex
+pub type Regex
 
 /// The details about a particular match:
 ///
@@ -59,15 +59,9 @@ pub fn compile(
   do_compile(pattern, options)
 }
 
-if erlang {
-  external fn do_compile(String, with: Options) -> Result(Regex, CompileError) =
-    "gleam_stdlib" "compile_regex"
-}
-
-if javascript {
-  external fn do_compile(String, with: Options) -> Result(Regex, CompileError) =
-    "../gleam_stdlib.mjs" "compile_regex"
-}
+@external(erlang, "gleam_stdlib", "compile_regex")
+@external(javascript, "../gleam_stdlib.mjs", "compile_regex")
+fn do_compile(a: String, with with: Options) -> Result(Regex, CompileError)
 
 /// Creates a new `Regex`.
 ///
@@ -117,15 +111,9 @@ pub fn check(with regex: Regex, content content: String) -> Bool {
   do_check(regex, content)
 }
 
-if erlang {
-  external fn do_check(Regex, String) -> Bool =
-    "gleam_stdlib" "regex_check"
-}
-
-if javascript {
-  external fn do_check(Regex, String) -> Bool =
-    "../gleam_stdlib.mjs" "regex_check"
-}
+@external(erlang, "gleam_stdlib", "regex_check")
+@external(javascript, "../gleam_stdlib.mjs", "regex_check")
+fn do_check(a: Regex, b: String) -> Bool
 
 /// Splits a string.
 ///
@@ -141,20 +129,19 @@ pub fn split(with regex: Regex, content string: String) -> List(String) {
   do_split(regex, string)
 }
 
-if erlang {
-  external fn do_split(Regex, String) -> List(String) =
-    "gleam_stdlib" "regex_split"
-}
-
-if javascript {
-  fn do_split(regex, string) -> List(String) {
-    js_split(string, regex)
-  }
+@target(erlang)
+@external(erlang, "gleam_stdlib", "regex_split")
+fn do_split(a: Regex, b: String) -> List(String)
 
-  external fn js_split(String, Regex) -> List(String) =
-    "../gleam_stdlib.mjs" "split"
+@target(javascript)
+fn do_split(regex, string) -> List(String) {
+  js_split(string, regex)
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "split")
+fn js_split(a: String, b: Regex) -> List(String)
+
 /// Collects all matches of the regular expression.
 ///
 /// ## Examples
@@ -222,12 +209,6 @@ pub fn scan(with regex: Regex, content string: String) -> List(Match) {
   do_scan(regex, string)
 }
 
-if erlang {
-  external fn do_scan(Regex, String) -> List(Match) =
-    "gleam_stdlib" "regex_scan"
-}
-
-if javascript {
-  external fn do_scan(Regex, String) -> List(Match) =
-    "../gleam_stdlib.mjs" "regex_scan"
-}
+@external(erlang, "gleam_stdlib", "regex_scan")
+@external(javascript, "../gleam_stdlib.mjs", "regex_scan")
+fn do_scan(a: Regex, b: String) -> List(Match)
diff --git a/src/gleam/set.gleam b/src/gleam/set.gleam
index 2440986..9ca8e44 100644
--- a/src/gleam/set.gleam
+++ b/src/gleam/set.gleam
@@ -2,21 +2,21 @@ import gleam/list
 import gleam/map.{Map}
 import gleam/result
 
-if erlang {
-  // A list is used as the map value as an empty list has the smallest
-  // representation in Erlang's binary format
-  type Token =
-    List(Nil)
+// A list is used as the map value as an empty list has the smallest
+// representation in Erlang's binary format
+@target(erlang)
+type Token =
+  List(Nil)
 
-  const token = []
-}
+@target(erlang)
+const token = []
 
-if javascript {
-  type Token =
-    Nil
+@target(javascript)
+type Token =
+  Nil
 
-  const token = Nil
-}
+@target(javascript)
+const token = Nil
 
 /// A set is a collection of unique members of the same type.
 ///
diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 2e6f28d..7cf4243 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -6,12 +6,12 @@ import gleam/list
 import gleam/option.{None, Option, Some}
 import gleam/order
 import gleam/string_builder.{StringBuilder}
-
-if erlang {
-  import gleam/bit_string
-  import gleam/dynamic.{Dynamic}
-  import gleam/result
-}
+@target(erlang)
+import gleam/bit_string
+@target(erlang)
+import gleam/dynamic.{Dynamic}
+@target(erlang)
+import gleam/result
 
 /// Determines if a `String` is empty.
 ///
@@ -57,15 +57,9 @@ pub fn length(string: String) -> Int {
   do_length(string)
 }
 
-if erlang {
-  external fn do_length(String) -> Int =
-    "string" "length"
-}
-
-if javascript {
-  external fn do_length(String) -> Int =
-    "../gleam_stdlib.mjs" "string_length"
-}
+@external(erlang, "string", "length")
+@external(javascript, "../gleam_stdlib.mjs", "string_length")
+fn do_length(a: String) -> Int
 
 /// Reverses a `String`.
 ///
@@ -83,22 +77,20 @@ pub fn reverse(string: String) -> String {
   do_reverse(string)
 }
 
-if erlang {
-  fn do_reverse(string: String) -> String {
-    string
-    |> string_builder.from_string
-    |> string_builder.reverse
-    |> string_builder.to_string
-  }
+@target(erlang)
+fn do_reverse(string: String) -> String {
+  string
+  |> string_builder.from_string
+  |> string_builder.reverse
+  |> string_builder.to_string
 }
 
-if javascript {
-  fn do_reverse(string: String) -> String {
-    string
-    |> to_graphemes
-    |> list.reverse
-    |> concat
-  }
+@target(javascript)
+fn do_reverse(string: String) -> String {
+  string
+  |> to_graphemes
+  |> list.reverse
+  |> concat
 }
 
 /// Creates a new `String` by replacing all occurrences of a given substring.
@@ -142,15 +134,9 @@ pub fn lowercase(string: String) -> String {
   do_lowercase(string)
 }
 
-if erlang {
-  external fn do_lowercase(String) -> String =
-    "string" "lowercase"
-}
-
-if javascript {
-  external fn do_lowercase(String) -> String =
-    "../gleam_stdlib.mjs" "lowercase"
-}
+@external(erlang, "string", "lowercase")
+@external(javascript, "../gleam_stdlib.mjs", "lowercase")
+fn do_lowercase(a: String) -> String
 
 /// Creates a new `String` with all the graphemes in the input `String` converted to
 /// uppercase.
@@ -168,15 +154,9 @@ pub fn uppercase(string: String) -> String {
   do_uppercase(string)
 }
 
-if erlang {
-  external fn do_uppercase(String) -> String =
-    "string" "uppercase"
-}
-
-if javascript {
-  external fn do_uppercase(String) -> String =
-    "../gleam_stdlib.mjs" "uppercase"
-}
+@external(erlang, "string", "uppercase")
+@external(javascript, "../gleam_stdlib.mjs", "uppercase")
+fn do_uppercase(a: String) -> String
 
 /// Compares two `String`s to see which is "larger" by comparing their graphemes.
 ///
@@ -205,15 +185,9 @@ pub fn compare(a: String, b: String) -> order.Order {
   }
 }
 
-if erlang {
-  external fn less_than(String, String) -> Bool =
-    "gleam_stdlib" "less_than"
-}
-
-if javascript {
-  external fn less_than(String, String) -> Bool =
-    "../gleam_stdlib.mjs" "less_than"
-}
+@external(erlang, "gleam_stdlib", "less_than")
+@external(javascript, "../gleam_stdlib.mjs", "less_than")
+fn less_than(a: String, b: String) -> Bool
 
 /// Takes a substring given a start and end grapheme indexes. Negative indexes
 /// are taken starting from the *end* of the list.
@@ -262,19 +236,17 @@ pub fn slice(from string: String, at_index idx: Int, length len: Int) -> String
   }
 }
 
-if erlang {
-  external fn do_slice(String, Int, Int) -> String =
-    "string" "slice"
-}
+@target(erlang)
+@external(erlang, "string", "slice")
+fn do_slice(a: String, b: Int, c: Int) -> String
 
-if javascript {
-  fn do_slice(string: String, idx: Int, len: Int) -> String {
-    string
-    |> to_graphemes
-    |> list.drop(idx)
-    |> list.take(len)
-    |> concat
-  }
+@target(javascript)
+fn do_slice(string: String, idx: Int, len: Int) -> String {
+  string
+  |> to_graphemes
+  |> list.drop(idx)
+  |> list.take(len)
+  |> concat
 }
 
 /// Drops contents of the first `String` that occur before the second `String`.
@@ -291,22 +263,21 @@ pub fn crop(from string: String, before substring: String) -> String {
   do_crop(string, substring)
 }
 
-if erlang {
-  fn do_crop(string: String, substring: String) -> String {
-    string
-    |> erl_contains(substring)
-    |> dynamic.string()
-    |> result.unwrap(string)
-  }
-
-  external fn erl_contains(String, String) -> Dynamic =
-    "string" "find"
+@target(erlang)
+fn do_crop(string: String, substring: String) -> String {
+  string
+  |> erl_contains(substring)
+  |> dynamic.string()
+  |> result.unwrap(string)
 }
 
-if javascript {
-  external fn do_crop(String, String) -> String =
-    "../gleam_stdlib.mjs" "crop_string"
-}
+@target(erlang)
+@external(erlang, "string", "find")
+fn erl_contains(a: String, b: String) -> Dynamic
+
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "crop_string")
+fn do_crop(a: String, b: String) -> String
 
 /// Drops *n* graphemes from the left side of a `String`.
 ///
@@ -363,24 +334,23 @@ pub fn contains(does haystack: String, contain needle: String) -> Bool {
   do_contains(haystack, needle)
 }
 
-if erlang {
-  fn do_contains(haystack: String, needle: String) -> Bool {
-    haystack
-    |> erl_contains(needle)
-    |> dynamic.bit_string
-    |> result.is_ok
-  }
+@target(erlang)
+fn do_contains(haystack: String, needle: String) -> Bool {
+  haystack
+  |> erl_contains(needle)
+  |> dynamic.bit_string
+  |> result.is_ok
 }
 
-if javascript {
-  fn do_contains(haystack: String, needle: String) -> Bool {
-    index_of(haystack, needle) != -1
-  }
-
-  external fn index_of(String, String) -> Int =
-    "../gleam_stdlib.mjs" "index_of"
+@target(javascript)
+fn do_contains(haystack: String, needle: String) -> Bool {
+  index_of(haystack, needle) != -1
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "index_of")
+fn index_of(a: String, b: String) -> Int
+
 /// Checks whether the first `String` starts with the second one.
 ///
 /// ## Examples
@@ -394,15 +364,9 @@ pub fn starts_with(string: String, prefix: String) -> Bool {
   do_starts_with(string, prefix)
 }
 
-if erlang {
-  external fn do_starts_with(String, String) -> Bool =
-    "gleam_stdlib" "string_starts_with"
-}
-
-if javascript {
-  external fn do_starts_with(String, String) -> Bool =
-    "../gleam_stdlib.mjs" "starts_with"
-}
+@external(erlang, "gleam_stdlib", "string_starts_with")
+@external(javascript, "../gleam_stdlib.mjs", "starts_with")
+fn do_starts_with(a: String, b: String) -> Bool
 
 /// Checks whether the first `String` ends with the second one.
 ///
@@ -417,15 +381,9 @@ pub fn ends_with(string: String, suffix: String) -> Bool {
   do_ends_with(string, suffix)
 }
 
-if erlang {
-  external fn do_ends_with(String, String) -> Bool =
-    "gleam_stdlib" "string_ends_with"
-}
-
-if javascript {
-  external fn do_ends_with(String, String) -> Bool =
-    "../gleam_stdlib.mjs" "ends_with"
-}
+@external(erlang, "gleam_stdlib", "string_ends_with")
+@external(javascript, "../gleam_stdlib.mjs", "ends_with")
+fn do_ends_with(a: String, b: String) -> Bool
 
 /// Creates a list of `String`s by splitting a given string on a given substring.
 ///
@@ -470,28 +428,24 @@ pub fn split_once(
   do_split_once(x, substring)
 }
 
-if erlang {
-  external fn erl_split(String, String) -> List(String) =
-    "string" "split"
-
-  fn do_split_once(
-    x: String,
-    substring: String,
-  ) -> Result(#(String, String), Nil) {
-    case erl_split(x, substring) {
-      [first, rest] -> Ok(#(first, rest))
-      _ -> Error(Nil)
-    }
+@target(erlang)
+@external(erlang, "string", "split")
+fn erl_split(a: String, b: String) -> List(String)
+
+@target(erlang)
+fn do_split_once(x: String, substring: String) -> Result(#(String, String), Nil) {
+  case erl_split(x, substring) {
+    [first, rest] -> Ok(#(first, rest))
+    _ -> Error(Nil)
   }
 }
 
-if javascript {
-  external fn do_split_once(
-    x: String,
-    substring: String,
-  ) -> Result(#(String, String), Nil) =
-    "../gleam_stdlib.mjs" "split_once"
-}
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "split_once")
+fn do_split_once(
+  x x: String,
+  substring substring: String,
+) -> Result(#(String, String), Nil)
 
 /// Creates a new `String` by joining two `String`s together.
 ///
@@ -565,18 +519,16 @@ pub fn join(strings: List(String), with separator: String) -> String {
   do_join(strings, separator)
 }
 
-if erlang {
-  fn do_join(strings: List(String), separator: String) -> String {
-    strings
-    |> list.intersperse(with: separator)
-    |> concat
-  }
+@target(erlang)
+fn do_join(strings: List(String), separator: String) -> String {
+  strings
+  |> list.intersperse(with: separator)
+  |> concat
 }
 
-if javascript {
-  external fn do_join(strings: List(String), string: String) -> String =
-    "../gleam_stdlib.mjs" "join"
-}
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "join")
+fn do_join(strings strings: List(String), string string: String) -> String
 
 /// Pads a `String` on the left until it has at least given number of graphemes.
 ///
@@ -660,26 +612,26 @@ pub fn trim(string: String) -> String {
   do_trim(string)
 }
 
-if erlang {
-  fn do_trim(string: String) -> String {
-    erl_trim(string, Both)
-  }
-
-  type Direction {
-    Leading
-    Trailing
-    Both
-  }
-
-  external fn erl_trim(String, Direction) -> String =
-    "string" "trim"
+@target(erlang)
+fn do_trim(string: String) -> String {
+  erl_trim(string, Both)
 }
 
-if javascript {
-  external fn do_trim(string: String) -> String =
-    "../gleam_stdlib.mjs" "trim"
+@target(erlang)
+type Direction {
+  Leading
+  Trailing
+  Both
 }
 
+@target(erlang)
+@external(erlang, "string", "trim")
+fn erl_trim(a: String, b: Direction) -> String
+
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "trim")
+fn do_trim(string string: String) -> String
+
 /// Removes whitespace on the left of a `String`.
 ///
 /// ## Examples
@@ -693,16 +645,14 @@ pub fn trim_left(string: String) -> String {
   do_trim_left(string)
 }
 
-if erlang {
-  fn do_trim_left(string: String) -> String {
-    erl_trim(string, Leading)
-  }
+@target(erlang)
+fn do_trim_left(string: String) -> String {
+  erl_trim(string, Leading)
 }
 
-if javascript {
-  external fn do_trim_left(string: String) -> String =
-    "../gleam_stdlib.mjs" "trim_left"
-}
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "trim_left")
+fn do_trim_left(string string: String) -> String
 
 /// Removes whitespace on the right of a `String`.
 ///
@@ -717,16 +667,14 @@ pub fn trim_right(string: String) -> String {
   do_trim_right(string)
 }
 
-if erlang {
-  fn do_trim_right(string: String) -> String {
-    erl_trim(string, Trailing)
-  }
+@target(erlang)
+fn do_trim_right(string: String) -> String {
+  erl_trim(string, Trailing)
 }
 
-if javascript {
-  external fn do_trim_right(string: String) -> String =
-    "../gleam_stdlib.mjs" "trim_right"
-}
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "trim_right")
+fn do_trim_right(string string: String) -> String
 
 /// Splits a non-empty `String` into its first element (head) and rest (tail).
 /// This lets you pattern match on `String`s exactly as you would with lists.
@@ -747,15 +695,9 @@ pub fn pop_grapheme(string: String) -> Result(#(String, String), Nil) {
   do_pop_grapheme(string)
 }
 
-if erlang {
-  external fn do_pop_grapheme(string: String) -> Result(#(String, String), Nil) =
-    "gleam_stdlib" "string_pop_grapheme"
-}
-
-if javascript {
-  external fn do_pop_grapheme(string: String) -> Result(#(String, String), Nil) =
-    "../gleam_stdlib.mjs" "pop_grapheme"
-}
+@external(erlang, "gleam_stdlib", "string_pop_grapheme")
+@external(javascript, "../gleam_stdlib.mjs", "pop_grapheme")
+fn do_pop_grapheme(string string: String) -> Result(#(String, String), Nil)
 
 /// Converts a `String` to a list of
 /// [graphemes](https://en.wikipedia.org/wiki/Grapheme).
@@ -777,15 +719,9 @@ fn do_to_graphemes(string: String, acc: List(String)) -> List(String) {
   }
 }
 
-if erlang {
-  external fn unsafe_int_to_utf_codepoint(Int) -> UtfCodepoint =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn unsafe_int_to_utf_codepoint(Int) -> UtfCodepoint =
-    "../gleam_stdlib.mjs" "codepoint"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "codepoint")
+fn unsafe_int_to_utf_codepoint(a: Int) -> UtfCodepoint
 
 /// Converts a `String` to a `List` of `UtfCodepoint`.
 ///
@@ -812,35 +748,35 @@ pub fn to_utf_codepoints(string: String) -> List(UtfCodepoint) {
   do_to_utf_codepoints(string)
 }
 
-if erlang {
-  fn do_to_utf_codepoints(string: String) -> List(UtfCodepoint) {
-    do_to_utf_codepoints_impl(bit_string.from_string(string), [])
-    |> list.reverse
-  }
-
-  fn do_to_utf_codepoints_impl(
-    bit_string: BitString,
-    acc: List(UtfCodepoint),
-  ) -> List(UtfCodepoint) {
-    case bit_string {
-      <<first:utf8_codepoint, rest:binary>> ->
-        do_to_utf_codepoints_impl(rest, [first, ..acc])
-      <<>> -> acc
-    }
-  }
+@target(erlang)
+fn do_to_utf_codepoints(string: String) -> List(UtfCodepoint) {
+  do_to_utf_codepoints_impl(bit_string.from_string(string), [])
+  |> list.reverse
 }
 
-if javascript {
-  fn do_to_utf_codepoints(string: String) -> List(UtfCodepoint) {
-    string
-    |> string_to_codepoint_integer_list
-    |> list.map(unsafe_int_to_utf_codepoint)
+@target(erlang)
+fn do_to_utf_codepoints_impl(
+  bit_string: BitString,
+  acc: List(UtfCodepoint),
+) -> List(UtfCodepoint) {
+  case bit_string {
+    <<first:utf8_codepoint, rest:binary>> ->
+      do_to_utf_codepoints_impl(rest, [first, ..acc])
+    <<>> -> acc
   }
+}
 
-  external fn string_to_codepoint_integer_list(String) -> List(Int) =
-    "../gleam_stdlib.mjs" "string_to_codepoint_integer_list"
+@target(javascript)
+fn do_to_utf_codepoints(string: String) -> List(UtfCodepoint) {
+  string
+  |> string_to_codepoint_integer_list
+  |> list.map(unsafe_int_to_utf_codepoint)
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "string_to_codepoint_integer_list")
+fn string_to_codepoint_integer_list(a: String) -> List(Int)
+
 /// Converts a `List` of `UtfCodepoint`s to a `String`.
 ///
 /// See <https://en.wikipedia.org/wiki/Code_point> and
@@ -866,38 +802,38 @@ pub fn from_utf_codepoints(utf_codepoints: List(UtfCodepoint)) -> String {
   do_from_utf_codepoints(utf_codepoints)
 }
 
-if erlang {
-  fn do_from_utf_codepoints(utf_codepoints: List(UtfCodepoint)) -> String {
-    let assert Ok(string) =
-      do_from_utf_codepoints_impl(utf_codepoints, bit_string.from_string(""))
-      |> bit_string.to_string
-    string
-  }
-
-  fn do_from_utf_codepoints_impl(
-    utf_codepoints: List(UtfCodepoint),
-    acc: BitString,
-  ) -> BitString {
-    case utf_codepoints {
-      [first, ..rest] ->
-        do_from_utf_codepoints_impl(
-          rest,
-          <<acc:bit_string, first:utf8_codepoint>>,
-        )
-      [] -> acc
-    }
-  }
+@target(erlang)
+fn do_from_utf_codepoints(utf_codepoints: List(UtfCodepoint)) -> String {
+  let assert Ok(string) =
+    do_from_utf_codepoints_impl(utf_codepoints, bit_string.from_string(""))
+    |> bit_string.to_string
+  string
 }
 
-if javascript {
-  fn do_from_utf_codepoints(utf_codepoints: List(UtfCodepoint)) -> String {
-    utf_codepoint_list_to_string(utf_codepoints)
+@target(erlang)
+fn do_from_utf_codepoints_impl(
+  utf_codepoints: List(UtfCodepoint),
+  acc: BitString,
+) -> BitString {
+  case utf_codepoints {
+    [first, ..rest] ->
+      do_from_utf_codepoints_impl(
+        rest,
+        <<acc:bit_string, first:utf8_codepoint>>,
+      )
+    [] -> acc
   }
+}
 
-  external fn utf_codepoint_list_to_string(List(UtfCodepoint)) -> String =
-    "../gleam_stdlib.mjs" "utf_codepoint_list_to_string"
+@target(javascript)
+fn do_from_utf_codepoints(utf_codepoints: List(UtfCodepoint)) -> String {
+  utf_codepoint_list_to_string(utf_codepoints)
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "utf_codepoint_list_to_string")
+fn utf_codepoint_list_to_string(a: List(UtfCodepoint)) -> String
+
 /// Converts an integer to a `UtfCodepoint`.
 ///
 /// Returns an `Error` if the integer does not represent a valid UTF codepoint.
@@ -924,15 +860,9 @@ pub fn utf_codepoint_to_int(cp: UtfCodepoint) -> Int {
   do_utf_codepoint_to_int(cp)
 }
 
-if erlang {
-  external fn do_utf_codepoint_to_int(cp: UtfCodepoint) -> Int =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_utf_codepoint_to_int(cp: UtfCodepoint) -> Int =
-    "../gleam_stdlib.mjs" "utf_codepoint_to_int"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "utf_codepoint_to_int")
+fn do_utf_codepoint_to_int(cp cp: UtfCodepoint) -> Int
 
 /// Converts a `String` into `Option(String)` where an empty `String` becomes
 /// `None`.
@@ -1027,15 +957,9 @@ pub fn inspect(term: anything) -> String {
   |> string_builder.to_string
 }
 
-if javascript {
-  external fn do_inspect(term: anything) -> StringBuilder =
-    "../gleam.mjs" "inspect"
-}
-
-if erlang {
-  external fn do_inspect(term: anything) -> StringBuilder =
-    "gleam_stdlib" "inspect"
-}
+@external(erlang, "gleam_stdlib", "inspect")
+@external(javascript, "../gleam.mjs", "inspect")
+fn do_inspect(term term: anything) -> StringBuilder
 
 /// Returns the number of bytes in a `String`.
 /// 
@@ -1046,12 +970,6 @@ pub fn byte_size(string: String) -> Int {
   do_byte_size(string)
 }
 
-if javascript {
-  external fn do_byte_size(String) -> Int =
-    "../gleam_stdlib.mjs" "byte_size"
-}
-
-if erlang {
-  external fn do_byte_size(String) -> Int =
-    "erlang" "byte_size"
-}
+@external(erlang, "erlang", "byte_size")
+@external(javascript, "../gleam_stdlib.mjs", "byte_size")
+fn do_byte_size(a: String) -> Int
diff --git a/src/gleam/string_builder.gleam b/src/gleam/string_builder.gleam
index bb88455..5792ca8 100644
--- a/src/gleam/string_builder.gleam
+++ b/src/gleam/string_builder.gleam
@@ -14,7 +14,7 @@ import gleam/list
 /// On Erlang this type is compatible with Erlang's iodata. On JavaScript this
 /// type is compatible with normal strings.
 ///
-pub external type StringBuilder
+pub type StringBuilder
 
 /// Create an empty `StringBuilder`. Useful as the start of a pipe chaining many
 /// builders together.
@@ -64,15 +64,9 @@ pub fn append_builder(
   do_append(builder, suffix)
 }
 
-if erlang {
-  external fn do_append(StringBuilder, StringBuilder) -> StringBuilder =
-    "gleam_stdlib" "iodata_append"
-}
-
-if javascript {
-  external fn do_append(StringBuilder, StringBuilder) -> StringBuilder =
-    "../gleam_stdlib.mjs" "add"
-}
+@external(erlang, "gleam_stdlib", "iodata_append")
+@external(javascript, "../gleam_stdlib.mjs", "add")
+fn do_append(a: StringBuilder, b: StringBuilder) -> StringBuilder
 
 /// Converts a list of strings into a builder.
 ///
@@ -82,15 +76,9 @@ pub fn from_strings(strings: List(String)) -> StringBuilder {
   do_from_strings(strings)
 }
 
-if erlang {
-  external fn do_from_strings(List(String)) -> StringBuilder =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_from_strings(List(String)) -> StringBuilder =
-    "../gleam_stdlib.mjs" "concat"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "concat")
+fn do_from_strings(a: List(String)) -> StringBuilder
 
 /// Joins a list of builders into a single builder.
 ///
@@ -100,15 +88,9 @@ pub fn concat(builders: List(StringBuilder)) -> StringBuilder {
   do_concat(builders)
 }
 
-if erlang {
-  external fn do_concat(List(StringBuilder)) -> StringBuilder =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_concat(List(StringBuilder)) -> StringBuilder =
-    "../gleam_stdlib.mjs" "concat"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "concat")
+fn do_concat(a: List(StringBuilder)) -> StringBuilder
 
 /// Converts a string into a builder.
 ///
@@ -118,15 +100,9 @@ pub fn from_string(string: String) -> StringBuilder {
   do_from_string(string)
 }
 
-if erlang {
-  external fn do_from_string(String) -> StringBuilder =
-    "gleam_stdlib" "identity"
-}
-
-if javascript {
-  external fn do_from_string(String) -> StringBuilder =
-    "../gleam_stdlib.mjs" "identity"
-}
+@external(erlang, "gleam_stdlib", "identity")
+@external(javascript, "../gleam_stdlib.mjs", "identity")
+fn do_from_string(a: String) -> StringBuilder
 
 /// Turns an `StringBuilder` into a `String`
 ///
@@ -137,15 +113,9 @@ pub fn to_string(builder: StringBuilder) -> String {
   do_to_string(builder)
 }
 
-if erlang {
-  external fn do_to_string(StringBuilder) -> String =
-    "unicode" "characters_to_binary"
-}
-
-if javascript {
-  external fn do_to_string(StringBuilder) -> String =
-    "../gleam_stdlib.mjs" "identity"
-}
+@external(erlang, "unicode", "characters_to_binary")
+@external(javascript, "../gleam_stdlib.mjs", "identity")
+fn do_to_string(a: StringBuilder) -> String
 
 /// Returns the size of the `StringBuilder` in bytes.
 ///
@@ -153,15 +123,9 @@ pub fn byte_size(builder: StringBuilder) -> Int {
   do_byte_size(builder)
 }
 
-if erlang {
-  external fn do_byte_size(StringBuilder) -> Int =
-    "erlang" "iolist_size"
-}
-
-if javascript {
-  external fn do_byte_size(StringBuilder) -> Int =
-    "../gleam_stdlib.mjs" "length"
-}
+@external(erlang, "erlang", "iolist_size")
+@external(javascript, "../gleam_stdlib.mjs", "length")
+fn do_byte_size(a: StringBuilder) -> Int
 
 /// Joins the given builders into a new builder separated with the given string
 ///
@@ -178,15 +142,9 @@ pub fn lowercase(builder: StringBuilder) -> StringBuilder {
   do_lowercase(builder)
 }
 
-if erlang {
-  external fn do_lowercase(StringBuilder) -> StringBuilder =
-    "string" "lowercase"
-}
-
-if javascript {
-  external fn do_lowercase(StringBuilder) -> StringBuilder =
-    "../gleam_stdlib.mjs" "lowercase"
-}
+@external(erlang, "string", "lowercase")
+@external(javascript, "../gleam_stdlib.mjs", "lowercase")
+fn do_lowercase(a: StringBuilder) -> StringBuilder
 
 /// Converts a builder to a new builder where the contents have been
 /// uppercased.
@@ -195,15 +153,9 @@ pub fn uppercase(builder: StringBuilder) -> StringBuilder {
   do_uppercase(builder)
 }
 
-if erlang {
-  external fn do_uppercase(StringBuilder) -> StringBuilder =
-    "string" "uppercase"
-}
-
-if javascript {
-  external fn do_uppercase(StringBuilder) -> StringBuilder =
-    "../gleam_stdlib.mjs" "uppercase"
-}
+@external(erlang, "string", "uppercase")
+@external(javascript, "../gleam_stdlib.mjs", "uppercase")
+fn do_uppercase(a: StringBuilder) -> StringBuilder
 
 /// Converts a builder to a new builder with the contents reversed.
 ///
@@ -211,50 +163,49 @@ pub fn reverse(builder: StringBuilder) -> StringBuilder {
   do_reverse(builder)
 }
 
-if erlang {
-  external fn do_reverse(StringBuilder) -> StringBuilder =
-    "string" "reverse"
-}
+@target(erlang)
+@external(erlang, "string", "reverse")
+fn do_reverse(a: StringBuilder) -> StringBuilder
 
-if javascript {
-  fn do_reverse(builder: StringBuilder) -> StringBuilder {
-    builder
-    |> to_string
-    |> do_to_graphemes
-    |> list.reverse
-    |> from_strings
-  }
-
-  external fn do_to_graphemes(string: String) -> List(String) =
-    "../gleam_stdlib.mjs" "graphemes"
+@target(javascript)
+fn do_reverse(builder: StringBuilder) -> StringBuilder {
+  builder
+  |> to_string
+  |> do_to_graphemes
+  |> list.reverse
+  |> from_strings
 }
 
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "graphemes")
+fn do_to_graphemes(string string: String) -> List(String)
+
 /// Splits a builder on a given pattern into a list of builders.
 ///
 pub fn split(iodata: StringBuilder, on pattern: String) -> List(StringBuilder) {
   do_split(iodata, pattern)
 }
 
-if erlang {
-  type Direction {
-    All
-  }
+@target(erlang)
+type Direction {
+  All
+}
 
-  external fn erl_split(StringBuilder, String, Direction) -> List(StringBuilder) =
-    "string" "split"
+@target(erlang)
+@external(erlang, "string", "split")
+fn erl_split(a: StringBuilder, b: String, c: Direction) -> List(StringBuilder)
 
-  fn do_split(iodata: StringBuilder, pattern: String) -> List(StringBuilder) {
-    erl_split(iodata, pattern, All)
-  }
+@target(erlang)
+fn do_split(iodata: StringBuilder, pattern: String) -> List(StringBuilder) {
+  erl_split(iodata, pattern, All)
 }
 
-if javascript {
-  external fn do_split(
-    builder: StringBuilder,
-    pattern: String,
-  ) -> List(StringBuilder) =
-    "../gleam_stdlib.mjs" "split"
-}
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "split")
+fn do_split(
+  builder builder: StringBuilder,
+  pattern pattern: String,
+) -> List(StringBuilder)
 
 /// Replaces all instances of a pattern with a given string substitute.
 ///
@@ -266,28 +217,27 @@ pub fn replace(
   do_replace(builder, pattern, substitute)
 }
 
-if erlang {
-  fn do_replace(
-    iodata: StringBuilder,
-    pattern: String,
-    substitute: String,
-  ) -> StringBuilder {
-    erl_replace(iodata, pattern, substitute, All)
-  }
-
-  external fn erl_replace(
-    StringBuilder,
-    String,
-    String,
-    Direction,
-  ) -> StringBuilder =
-    "string" "replace"
+@target(erlang)
+fn do_replace(
+  iodata: StringBuilder,
+  pattern: String,
+  substitute: String,
+) -> StringBuilder {
+  erl_replace(iodata, pattern, substitute, All)
 }
 
-if javascript {
-  external fn do_replace(StringBuilder, String, String) -> StringBuilder =
-    "../gleam_stdlib.mjs" "string_replace"
-}
+@target(erlang)
+@external(erlang, "string", "replace")
+fn erl_replace(
+  a: StringBuilder,
+  b: String,
+  c: String,
+  d: Direction,
+) -> StringBuilder
+
+@target(javascript)
+@external(javascript, "../gleam_stdlib.mjs", "string_replace")
+fn do_replace(a: StringBuilder, b: String, c: String) -> StringBuilder
 
 /// Compares two builders to determine if they have the same textual content.
 ///
@@ -311,15 +261,9 @@ pub fn is_equal(a: StringBuilder, b: StringBuilder) -> Bool {
   do_is_equal(a, b)
 }
 
-if erlang {
-  external fn do_is_equal(StringBuilder, StringBuilder) -> Bool =
-    "string" "equal"
-}
-
-if javascript {
-  external fn do_is_equal(StringBuilder, StringBuilder) -> Bool =
-    "../gleam_stdlib.mjs" "equal"
-}
+@external(erlang, "string", "equal")
+@external(javascript, "../gleam_stdlib.mjs", "equal")
+fn do_is_equal(a: StringBuilder, b: StringBuilder) -> Bool
 
 /// Inspects a builder to determine if it is equivalent to an empty string.
 ///
@@ -344,13 +288,11 @@ pub fn is_empty(builder: StringBuilder) -> Bool {
   do_is_empty(builder)
 }
 
-if erlang {
-  external fn do_is_empty(StringBuilder) -> Bool =
-    "string" "is_empty"
-}
+@target(erlang)
+@external(erlang, "string", "is_empty")
+fn do_is_empty(a: StringBuilder) -> Bool
 
-if javascript {
-  fn do_is_empty(builder: StringBuilder) -> Bool {
-    from_string("") == builder
-  }
+@target(javascript)
+fn do_is_empty(builder: StringBuilder) -> Bool {
+  from_string("") == builder
 }
diff --git a/src/gleam/uri.gleam b/src/gleam/uri.gleam
index 3fdfc6d..2565771 100644
--- a/src/gleam/uri.gleam
+++ b/src/gleam/uri.gleam
@@ -12,12 +12,12 @@ import gleam/list
 import gleam/option.{None, Option, Some}
 import gleam/string
 import gleam/string_builder.{StringBuilder}
-
-if javascript {
-  import gleam/pair
-  import gleam/regex
-  import gleam/result
-}
+@target(javascript)
+import gleam/pair
+@target(javascript)
+import gleam/regex
+@target(javascript)
+import gleam/result
 
 /// Type representing holding the parsed components of an URI.
 /// All components of a URI are optional, except the path.
@@ -60,135 +60,139 @@ pub fn parse(uri_string: String) -> Result(Uri, Nil) {
   do_parse(uri_string)
 }
 
-if erlang {
-  external fn do_parse(String) -> Result(Uri, Nil) =
-    "gleam_stdlib" "uri_parse"
-}
-
-if javascript {
-  fn do_parse(uri_string: String) -> Result(Uri, Nil) {
-    // From https://tools.ietf.org/html/rfc3986#appendix-B
-    let pattern =
-      //    12                        3  4          5       6  7        8
-      "^(([a-z][a-z0-9\\+\\-\\.]*):)?(//([^/?#]*))?([^?#]*)(\\?([^#]*))?(#.*)?"
-    let matches =
-      pattern
-      |> regex_submatches(uri_string)
-      |> pad_list(8)
+@target(erlang)
+@external(erlang, "gleam_stdlib", "uri_parse")
+fn do_parse(a: String) -> Result(Uri, Nil)
+
+@target(javascript)
+fn do_parse(uri_string: String) -> Result(Uri, Nil) {
+  // From https://tools.ietf.org/html/rfc3986#appendix-B
+  let pattern =
+    //    12                        3  4          5       6  7        8
+    "^(([a-z][a-z0-9\\+\\-\\.]*):)?(//([^/?#]*))?([^?#]*)(\\?([^#]*))?(#.*)?"
+  let matches =
+    pattern
+    |> regex_submatches(uri_string)
+    |> pad_list(8)
+
+  let #(scheme, authority, path, query, fragment) = case matches {
+    [
+      _scheme_with_colon,
+      scheme,
+      authority_with_slashes,
+      _authority,
+      path,
+      query_with_question_mark,
+      _query,
+      fragment,
+    ] -> #(
+      scheme,
+      authority_with_slashes,
+      path,
+      query_with_question_mark,
+      fragment,
+    )
+    _ -> #(None, None, None, None, None)
+  }
 
-    let #(scheme, authority, path, query, fragment) = case matches {
-      [
-        _scheme_with_colon,
-        scheme,
-        authority_with_slashes,
-        _authority,
-        path,
-        query_with_question_mark,
-        _query,
-        fragment,
-      ] -> #(
-        scheme,
-        authority_with_slashes,
-        path,
-        query_with_question_mark,
-        fragment,
-      )
-      _ -> #(None, None, None, None, None)
-    }
+  let scheme = noneify_empty_string(scheme)
+  let path = option.unwrap(path, "")
+  let query = noneify_query(query)
+  let #(userinfo, host, port) = split_authority(authority)
+  let fragment =
+    fragment
+    |> option.to_result(Nil)
+    |> result.try(string.pop_grapheme)
+    |> result.map(pair.second)
+    |> option.from_result
+  let scheme =
+    scheme
+    |> noneify_empty_string
+    |> option.map(string.lowercase)
+  Ok(Uri(
+    scheme: scheme,
+    userinfo: userinfo,
+    host: host,
+    port: port,
+    path: path,
+    query: query,
+    fragment: fragment,
+  ))
+}
 
-    let scheme = noneify_empty_string(scheme)
-    let path = option.unwrap(path, "")
-    let query = noneify_query(query)
-    let #(userinfo, host, port) = split_authority(authority)
-    let fragment =
-      fragment
-      |> option.to_result(Nil)
-      |> result.try(string.pop_grapheme)
-      |> result.map(pair.second)
-      |> option.from_result
-    let scheme =
-      scheme
-      |> noneify_empty_string
-      |> option.map(string.lowercase)
-    Ok(Uri(
-      scheme: scheme,
-      userinfo: userinfo,
-      host: host,
-      port: port,
-      path: path,
-      query: query,
-      fragment: fragment,
-    ))
-  }
+@target(javascript)
+fn regex_submatches(pattern: String, string: String) -> List(Option(String)) {
+  pattern
+  |> regex.compile(regex.Options(case_insensitive: True, multi_line: False))
+  |> result.nil_error
+  |> result.map(regex.scan(_, string))
+  |> result.try(list.first)
+  |> result.map(fn(m: regex.Match) { m.submatches })
+  |> result.unwrap([])
+}
 
-  fn regex_submatches(pattern: String, string: String) -> List(Option(String)) {
-    pattern
-    |> regex.compile(regex.Options(case_insensitive: True, multi_line: False))
-    |> result.nil_error
-    |> result.map(regex.scan(_, string))
-    |> result.try(list.first)
-    |> result.map(fn(m: regex.Match) { m.submatches })
-    |> result.unwrap([])
+@target(javascript)
+fn noneify_query(x: Option(String)) -> Option(String) {
+  case x {
+    None -> None
+    Some(x) ->
+      case string.pop_grapheme(x) {
+        Ok(#("?", query)) -> Some(query)
+        _ -> None
+      }
   }
+}
 
-  fn noneify_query(x: Option(String)) -> Option(String) {
-    case x {
-      None -> None
-      Some(x) ->
-        case string.pop_grapheme(x) {
-          Ok(#("?", query)) -> Some(query)
-          _ -> None
-        }
-    }
-  }
-
-  fn noneify_empty_string(x: Option(String)) -> Option(String) {
-    case x {
-      Some("") | None -> None
-      Some(_) -> x
-    }
+@target(javascript)
+fn noneify_empty_string(x: Option(String)) -> Option(String) {
+  case x {
+    Some("") | None -> None
+    Some(_) -> x
   }
+}
 
-  // Split an authority into its userinfo, host and port parts.
-  fn split_authority(
-    authority: Option(String),
-  ) -> #(Option(String), Option(String), Option(Int)) {
-    case option.unwrap(authority, "") {
-      "" -> #(None, None, None)
-      "//" -> #(None, Some(""), None)
-      authority -> {
-        let matches =
-          "^(//)?((.*)@)?(\\[[a-zA-Z0-9:.]*\\]|[^:]*)(:(\\d*))?"
-          |> regex_submatches(authority)
-          |> pad_list(6)
-        case matches {
-          [_, _, userinfo, host, _, port] -> {
-            let userinfo = noneify_empty_string(userinfo)
-            let host = noneify_empty_string(host)
-            let port =
-              port
-              |> option.unwrap("")
-              |> int.parse
-              |> option.from_result
-            #(userinfo, host, port)
-          }
-          _ -> #(None, None, None)
+// Split an authority into its userinfo, host and port parts.
+@target(javascript)
+fn split_authority(
+  authority: Option(String),
+) -> #(Option(String), Option(String), Option(Int)) {
+  case option.unwrap(authority, "") {
+    "" -> #(None, None, None)
+    "//" -> #(None, Some(""), None)
+    authority -> {
+      let matches =
+        "^(//)?((.*)@)?(\\[[a-zA-Z0-9:.]*\\]|[^:]*)(:(\\d*))?"
+        |> regex_submatches(authority)
+        |> pad_list(6)
+      case matches {
+        [_, _, userinfo, host, _, port] -> {
+          let userinfo = noneify_empty_string(userinfo)
+          let host = noneify_empty_string(host)
+          let port =
+            port
+            |> option.unwrap("")
+            |> int.parse
+            |> option.from_result
+          #(userinfo, host, port)
         }
+        _ -> #(None, None, None)
       }
     }
   }
+}
 
-  fn pad_list(list: List(Option(a)), size: Int) -> List(Option(a)) {
-    list
-    |> list.append(list.repeat(None, extra_required(list, size)))
-  }
+@target(javascript)
+fn pad_list(list: List(Option(a)), size: Int) -> List(Option(a)) {
+  list
+  |> list.append(list.repeat(None, extra_required(list, size)))
+}
 
-  fn extra_required(list: List(a), remaining: Int) -> Int {
-    case list {
-      _ if remaining == 0 -> 0
-      [] -> remaining
-      [_, ..xs] -> extra_required(xs, remaining - 1)
-    }
+@target(javascript)
+fn extra_required(list: List(a), remaining: Int) -> Int {
+  case list {
+    _ if remaining == 0 -> 0
+    [] -> remaining
+    [_, ..xs] -> extra_required(xs, remaining - 1)
   }
 }
 
@@ -208,15 +212,9 @@ pub fn parse_query(query: String) -> Result(List(#(String, String)), Nil) {
   do_parse_query(query)
 }
 
-if erlang {
-  external fn do_parse_query(String) -> Result(List(#(String, String)), Nil) =
-    "gleam_stdlib" "parse_query"
-}
-
-if javascript {
-  external fn do_parse_query(String) -> Result(List(#(String, String)), Nil) =
-    "../gleam_stdlib.mjs" "parse_query"
-}
+@external(erlang, "gleam_stdlib", "parse_query")
+@external(javascript, "../gleam_stdlib.mjs", "parse_query")
+fn do_parse_query(a: String) -> Result(List(#(String, String)), Nil)
 
 /// Encodes a list of key value pairs as a URI query string.
 ///
@@ -258,15 +256,9 @@ pub fn percent_encode(value: String) -> String {
   do_percent_encode(value)
 }
 
-if erlang {
-  external fn do_percent_encode(String) -> String =
-    "gleam_stdlib" "percent_encode"
-}
-
-if javascript {
-  external fn do_percent_encode(String) -> String =
-    "../gleam_stdlib.mjs" "percent_encode"
-}
+@external(erlang, "gleam_stdlib", "percent_encode")
+@external(javascript, "../gleam_stdlib.mjs", "percent_encode")
+fn do_percent_encode(a: String) -> String
 
 /// Decodes a percent encoded string.
 ///
@@ -281,15 +273,9 @@ pub fn percent_decode(value: String) -> Result(String, Nil) {
   do_percent_decode(value)
 }
 
-if erlang {
-  external fn do_percent_decode(String) -> Result(String, Nil) =
-    "gleam_stdlib" "percent_decode"
-}
-
-if javascript {
-  external fn do_percent_decode(String) -> Result(String, Nil) =
-    "../gleam_stdlib.mjs" "percent_decode"
-}
+@external(erlang, "gleam_stdlib", "percent_decode")
+@external(javascript, "../gleam_stdlib.mjs", "percent_decode")
+fn do_percent_decode(a: String) -> Result(String, Nil)
 
 fn do_remove_dot_segments(
   input: List(String),