fix-721

9 files changed, 722 insertions, 720 deletions

diff --git a/src/gleam/bit_array.gleam b/src/gleam/bit_array.gleam
index 14db902..2c70d14 100644
--- a/src/gleam/bit_array.gleam
+++ b/src/gleam/bit_array.gleam
@@ -48,20 +48,20 @@ pub fn slice(
 /// Tests to see whether a bit array is valid UTF-8.
 ///
 pub fn is_utf8(bits: BitArray) -> Bool {
-  do_is_utf8(bits)
+  is_utf8_loop(bits)
 }
 
 @target(erlang)
-fn do_is_utf8(bits: BitArray) -> Bool {
+fn is_utf8_loop(bits: BitArray) -> Bool {
   case bits {
     <<>> -> True
-    <<_:utf8, rest:bytes>> -> do_is_utf8(rest)
+    <<_:utf8, rest:bytes>> -> is_utf8_loop(rest)
     _ -> False
   }
 }
 
 @target(javascript)
-fn do_is_utf8(bits: BitArray) -> Bool {
+fn is_utf8_loop(bits: BitArray) -> Bool {
   case to_string(bits) {
     Ok(_) -> True
     _ -> False
@@ -158,11 +158,11 @@ pub fn base16_decode(input: String) -> Result(BitArray, Nil)
 /// ```
 ///
 pub fn inspect(input: BitArray) -> String {
-  do_inspect(input, "<<") <> ">>"
+  inspect_loop(input, "<<") <> ">>"
 }
 
 @external(javascript, "../gleam_stdlib.mjs", "bit_array_inspect")
-fn do_inspect(input: BitArray, accumulator: String) -> String {
+fn inspect_loop(input: BitArray, accumulator: String) -> String {
   case input {
     <<>> -> accumulator
 
@@ -181,8 +181,7 @@ fn do_inspect(input: BitArray, accumulator: String) -> String {
       }
 
       let accumulator = accumulator <> int.to_string(x) <> suffix
-
-      do_inspect(rest, accumulator)
+      inspect_loop(rest, accumulator)
     }
 
     _ -> accumulator
diff --git a/src/gleam/dict.gleam b/src/gleam/dict.gleam
index 10b5544..4697c8d 100644
--- a/src/gleam/dict.gleam
+++ b/src/gleam/dict.gleam
@@ -223,7 +223,7 @@ pub fn keys(dict: Dict(k, v)) -> List(k) {
 @external(erlang, "maps", "keys")
 fn do_keys(dict: Dict(k, v)) -> List(k) {
   let list_of_pairs = to_list(dict)
-  do_keys_acc(list_of_pairs, [])
+  do_keys_loop(list_of_pairs, [])
 }
 
 fn reverse_and_concat(remaining: List(a), accumulator: List(a)) -> List(a) {
@@ -233,10 +233,10 @@ fn reverse_and_concat(remaining: List(a), accumulator: List(a)) -> List(a) {
   }
 }
 
-fn do_keys_acc(list: List(#(k, v)), acc: List(k)) -> List(k) {
+fn do_keys_loop(list: List(#(k, v)), acc: List(k)) -> List(k) {
   case list {
     [] -> reverse_and_concat(acc, [])
-    [first, ..rest] -> do_keys_acc(rest, [first.0, ..acc])
+    [first, ..rest] -> do_keys_loop(rest, [first.0, ..acc])
   }
 }
 
@@ -260,13 +260,13 @@ pub fn values(dict: Dict(k, v)) -> List(v) {
 @external(erlang, "maps", "values")
 fn do_values(dict: Dict(k, v)) -> List(v) {
   let list_of_pairs = to_list(dict)
-  do_values_acc(list_of_pairs, [])
+  do_values_loop(list_of_pairs, [])
 }
 
-fn do_values_acc(list: List(#(k, v)), acc: List(v)) -> List(v) {
+fn do_values_loop(list: List(#(k, v)), acc: List(v)) -> List(v) {
   case list {
     [] -> reverse_and_concat(acc, [])
-    [first, ..rest] -> do_values_acc(rest, [first.1, ..acc])
+    [first, ..rest] -> do_values_loop(rest, [first.1, ..acc])
   }
 }
 
@@ -302,8 +302,8 @@ fn do_filter(f: fn(k, v) -> Bool, dict: Dict(k, v)) -> Dict(k, v) {
       _ -> dict
     }
   }
-  dict
-  |> fold(from: new(), with: insert)
+
+  fold(dict, from: new(), with: insert)
 }
 
 /// Creates a new dict from a given dict, only including any entries for which the
@@ -329,10 +329,10 @@ pub fn take(from dict: Dict(k, v), keeping desired_keys: List(k)) -> Dict(k, v)
 
 @external(erlang, "maps", "with")
 fn do_take(desired_keys: List(k), dict: Dict(k, v)) -> Dict(k, v) {
-  insert_taken(dict, desired_keys, new())
+  do_take_loop(dict, desired_keys, new())
 }
 
-fn insert_taken(
+fn do_take_loop(
   dict: Dict(k, v),
   desired_keys: List(k),
   acc: Dict(k, v),
@@ -345,7 +345,7 @@ fn insert_taken(
   }
   case desired_keys {
     [] -> acc
-    [first, ..rest] -> insert_taken(dict, rest, insert(acc, first))
+    [first, ..rest] -> do_take_loop(dict, rest, insert(acc, first))
   }
 }
 
@@ -470,13 +470,6 @@ pub fn upsert(
   |> insert(dict, key, _)
 }
 
-fn do_fold(list: List(#(k, v)), initial: acc, fun: fn(acc, k, v) -> acc) -> acc {
-  case list {
-    [] -> initial
-    [#(k, v), ..rest] -> do_fold(rest, fun(initial, k, v), fun)
-  }
-}
-
 /// Combines all entries into a single value by calling a given function on each
 /// one.
 ///
@@ -507,9 +500,18 @@ pub fn fold(
   from initial: acc,
   with fun: fn(acc, k, v) -> acc,
 ) -> acc {
-  dict
-  |> to_list
-  |> do_fold(initial, fun)
+  fold_loop(to_list(dict), initial, fun)
+}
+
+fn fold_loop(
+  list: List(#(k, v)),
+  initial: acc,
+  fun: fn(acc, k, v) -> acc,
+) -> acc {
+  case list {
+    [] -> initial
+    [#(k, v), ..rest] -> fold_loop(rest, fun(initial, k, v), fun)
+  }
 }
 
 /// Calls a function for each key and value in a dict, discarding the return
diff --git a/src/gleam/float.gleam b/src/gleam/float.gleam
index 7030caa..a7d6dc8 100644
--- a/src/gleam/float.gleam
+++ b/src/gleam/float.gleam
@@ -403,14 +403,13 @@ pub fn negate(x: Float) -> Float {
 /// ```
 ///
 pub fn sum(numbers: List(Float)) -> Float {
-  numbers
-  |> do_sum(0.0)
+  sum_loop(numbers, 0.0)
 }
 
-fn do_sum(numbers: List(Float), initial: Float) -> Float {
+fn sum_loop(numbers: List(Float), initial: Float) -> Float {
   case numbers {
+    [x, ..rest] -> sum_loop(rest, x +. initial)
     [] -> initial
-    [x, ..rest] -> do_sum(rest, x +. initial)
   }
 }
 
@@ -426,14 +425,14 @@ fn do_sum(numbers: List(Float), initial: Float) -> Float {
 pub fn product(numbers: List(Float)) -> Float {
   case numbers {
     [] -> 1.0
-    _ -> do_product(numbers, 1.0)
+    _ -> product_loop(numbers, 1.0)
   }
 }
 
-fn do_product(numbers: List(Float), initial: Float) -> Float {
+fn product_loop(numbers: List(Float), initial: Float) -> Float {
   case numbers {
+    [x, ..rest] -> product_loop(rest, x *. initial)
     [] -> initial
-    [x, ..rest] -> do_product(rest, x *. initial)
   }
 }
 
diff --git a/src/gleam/int.gleam b/src/gleam/int.gleam
index 5d60b6e..de039d5 100644
--- a/src/gleam/int.gleam
+++ b/src/gleam/int.gleam
@@ -427,14 +427,13 @@ pub fn negate(x: Int) -> Int {
 /// ```
 ///
 pub fn sum(numbers: List(Int)) -> Int {
-  numbers
-  |> do_sum(0)
+  sum_loop(numbers, 0)
 }
 
-fn do_sum(numbers: List(Int), initial: Int) -> Int {
+fn sum_loop(numbers: List(Int), initial: Int) -> Int {
   case numbers {
+    [x, ..rest] -> sum_loop(rest, x + initial)
     [] -> initial
-    [x, ..rest] -> do_sum(rest, x + initial)
   }
 }
 
@@ -450,14 +449,14 @@ fn do_sum(numbers: List(Int), initial: Int) -> Int {
 pub fn product(numbers: List(Int)) -> Int {
   case numbers {
     [] -> 1
-    _ -> do_product(numbers, 1)
+    _ -> product_loop(numbers, 1)
   }
 }
 
-fn do_product(numbers: List(Int), initial: Int) -> Int {
+fn product_loop(numbers: List(Int), initial: Int) -> Int {
   case numbers {
+    [x, ..rest] -> product_loop(rest, x * initial)
     [] -> initial
-    [x, ..rest] -> do_product(rest, x * initial)
   }
 }
 
@@ -479,14 +478,14 @@ fn do_product(numbers: List(Int), initial: Int) -> Int {
 pub fn digits(x: Int, base: Int) -> Result(List(Int), Nil) {
   case base < 2 {
     True -> Error(Nil)
-    False -> Ok(do_digits(x, base, []))
+    False -> Ok(digits_loop(x, base, []))
   }
 }
 
-fn do_digits(x: Int, base: Int, acc: List(Int)) -> List(Int) {
+fn digits_loop(x: Int, base: Int, acc: List(Int)) -> List(Int) {
   case absolute_value(x) < base {
     True -> [x, ..acc]
-    False -> do_digits(x / base, base, [x % base, ..acc])
+    False -> digits_loop(x / base, base, [x % base, ..acc])
   }
 }
 
@@ -513,15 +512,15 @@ fn do_digits(x: Int, base: Int, acc: List(Int)) -> List(Int) {
 pub fn undigits(numbers: List(Int), base: Int) -> Result(Int, Nil) {
   case base < 2 {
     True -> Error(Nil)
-    False -> do_undigits(numbers, base, 0)
+    False -> undigits_loop(numbers, base, 0)
   }
 }
 
-fn do_undigits(numbers: List(Int), base: Int, acc: Int) -> Result(Int, Nil) {
+fn undigits_loop(numbers: List(Int), base: Int, acc: Int) -> Result(Int, Nil) {
   case numbers {
     [] -> Ok(acc)
     [digit, ..] if digit >= base -> Error(Nil)
-    [digit, ..rest] -> do_undigits(rest, base, acc * base + digit)
+    [digit, ..rest] -> undigits_loop(rest, base, acc * base + digit)
   }
 }
 
diff --git a/src/gleam/iterator.gleam b/src/gleam/iterator.gleam
index 3232a12..812436b 100644
--- a/src/gleam/iterator.gleam
+++ b/src/gleam/iterator.gleam
@@ -38,19 +38,6 @@ fn stop() -> Action(element) {
   Stop
 }
 
-// Creating Iterators
-fn do_unfold(
-  initial: acc,
-  f: fn(acc) -> Step(element, acc),
-) -> fn() -> Action(element) {
-  fn() {
-    case f(initial) {
-      Next(x, acc) -> Continue(x, do_unfold(acc, f))
-      Done -> Stop
-    }
-  }
-}
-
 /// Creates an iterator from a given function and accumulator.
 ///
 /// The function is called on the accumulator and returns either `Done`,
@@ -77,10 +64,23 @@ pub fn unfold(
   with f: fn(acc) -> Step(element, acc),
 ) -> Iterator(element) {
   initial
-  |> do_unfold(f)
+  |> unfold_loop(f)
   |> Iterator
 }
 
+// Creating Iterators
+fn unfold_loop(
+  initial: acc,
+  f: fn(acc) -> Step(element, acc),
+) -> fn() -> Action(element) {
+  fn() {
+    case f(initial) {
+      Next(x, acc) -> Continue(x, unfold_loop(acc, f))
+      Done -> Stop
+    }
+  }
+}
+
 /// Creates an iterator that yields values created by calling a given function
 /// repeatedly.
 ///
@@ -131,7 +131,7 @@ pub fn from_list(list: List(element)) -> Iterator(element) {
 }
 
 // Consuming Iterators
-fn do_transform(
+fn transform_loop(
   continuation: fn() -> Action(a),
   state: acc,
   f: fn(acc, a) -> Step(b, acc),
@@ -143,7 +143,7 @@ fn do_transform(
         case f(state, el) {
           Done -> Stop
           Next(yield, next_state) ->
-            Continue(yield, do_transform(next, next_state, f))
+            Continue(yield, transform_loop(next, next_state, f))
         }
     }
   }
@@ -171,17 +171,17 @@ pub fn transform(
   from initial: acc,
   with f: fn(acc, a) -> Step(b, acc),
 ) -> Iterator(b) {
-  do_transform(iterator.continuation, initial, f)
+  transform_loop(iterator.continuation, initial, f)
   |> Iterator
 }
 
-fn do_fold(
+fn fold_loop(
   continuation: fn() -> Action(e),
   f: fn(acc, e) -> acc,
   accumulator: acc,
 ) -> acc {
   case continuation() {
-    Continue(elem, next) -> do_fold(next, f, f(accumulator, elem))
+    Continue(elem, next) -> fold_loop(next, f, f(accumulator, elem))
     Stop -> accumulator
   }
 }
@@ -209,7 +209,7 @@ pub fn fold(
   with f: fn(acc, e) -> acc,
 ) -> acc {
   iterator.continuation
-  |> do_fold(f, initial)
+  |> fold_loop(f, initial)
 }
 
 // TODO: test
@@ -270,19 +270,6 @@ pub fn step(iterator: Iterator(e)) -> Step(e, Iterator(e)) {
   }
 }
 
-fn do_take(continuation: fn() -> Action(e), desired: Int) -> fn() -> Action(e) {
-  fn() {
-    case desired > 0 {
-      False -> Stop
-      True ->
-        case continuation() {
-          Stop -> Stop
-          Continue(e, next) -> Continue(e, do_take(next, desired - 1))
-        }
-    }
-  }
-}
-
 /// Creates an iterator that only yields the first `desired` elements.
 ///
 /// If the iterator does not have enough elements all of them are yielded.
@@ -305,18 +292,20 @@ fn do_take(continuation: fn() -> Action(e), desired: Int) -> fn() -> Action(e) {
 ///
 pub fn take(from iterator: Iterator(e), up_to desired: Int) -> Iterator(e) {
   iterator.continuation
-  |> do_take(desired)
+  |> take_loop(desired)
   |> Iterator
 }
 
-fn do_drop(continuation: fn() -> Action(e), desired: Int) -> Action(e) {
-  case continuation() {
-    Stop -> Stop
-    Continue(e, next) ->
-      case desired > 0 {
-        True -> do_drop(next, desired - 1)
-        False -> Continue(e, next)
-      }
+fn take_loop(continuation: fn() -> Action(e), desired: Int) -> fn() -> Action(e) {
+  fn() {
+    case desired > 0 {
+      False -> Stop
+      True ->
+        case continuation() {
+          Stop -> Stop
+          Continue(e, next) -> Continue(e, take_loop(next, desired - 1))
+        }
+    }
   }
 }
 
@@ -346,16 +335,18 @@ fn do_drop(continuation: fn() -> Action(e), desired: Int) -> Action(e) {
 /// ```
 ///
 pub fn drop(from iterator: Iterator(e), up_to desired: Int) -> Iterator(e) {
-  fn() { do_drop(iterator.continuation, desired) }
+  fn() { drop_loop(iterator.continuation, desired) }
   |> Iterator
 }
 
-fn do_map(continuation: fn() -> Action(a), f: fn(a) -> b) -> fn() -> Action(b) {
-  fn() {
-    case continuation() {
-      Stop -> Stop
-      Continue(e, continuation) -> Continue(f(e), do_map(continuation, f))
-    }
+fn drop_loop(continuation: fn() -> Action(e), desired: Int) -> Action(e) {
+  case continuation() {
+    Stop -> Stop
+    Continue(e, next) ->
+      case desired > 0 {
+        True -> drop_loop(next, desired - 1)
+        False -> Continue(e, next)
+      }
   }
 }
 
@@ -378,24 +369,15 @@ fn do_map(continuation: fn() -> Action(a), f: fn(a) -> b) -> fn() -> Action(b) {
 ///
 pub fn map(over iterator: Iterator(a), with f: fn(a) -> b) -> Iterator(b) {
   iterator.continuation
-  |> do_map(f)
+  |> map_loop(f)
   |> Iterator
 }
 
-fn do_map2(
-  continuation1: fn() -> Action(a),
-  continuation2: fn() -> Action(b),
-  with fun: fn(a, b) -> c,
-) -> fn() -> Action(c) {
+fn map_loop(continuation: fn() -> Action(a), f: fn(a) -> b) -> fn() -> Action(b) {
   fn() {
-    case continuation1() {
+    case continuation() {
       Stop -> Stop
-      Continue(a, next_a) ->
-        case continuation2() {
-          Stop -> Stop
-          Continue(b, next_b) ->
-            Continue(fun(a, b), do_map2(next_a, next_b, fun))
-        }
+      Continue(e, continuation) -> Continue(f(e), map_loop(continuation, f))
     }
   }
 }
@@ -428,14 +410,25 @@ pub fn map2(
   iterator2: Iterator(b),
   with fun: fn(a, b) -> c,
 ) -> Iterator(c) {
-  do_map2(iterator1.continuation, iterator2.continuation, fun)
+  map2_loop(iterator1.continuation, iterator2.continuation, fun)
   |> Iterator
 }
 
-fn do_append(first: fn() -> Action(a), second: fn() -> Action(a)) -> Action(a) {
-  case first() {
-    Continue(e, first) -> Continue(e, fn() { do_append(first, second) })
-    Stop -> second()
+fn map2_loop(
+  continuation1: fn() -> Action(a),
+  continuation2: fn() -> Action(b),
+  with fun: fn(a, b) -> c,
+) -> fn() -> Action(c) {
+  fn() {
+    case continuation1() {
+      Stop -> Stop
+      Continue(a, next_a) ->
+        case continuation2() {
+          Stop -> Stop
+          Continue(b, next_b) ->
+            Continue(fun(a, b), map2_loop(next_a, next_b, fun))
+        }
+    }
   }
 }
 
@@ -454,15 +447,14 @@ fn do_append(first: fn() -> Action(a), second: fn() -> Action(a)) -> Action(a) {
 /// ```
 ///
 pub fn append(to first: Iterator(a), suffix second: Iterator(a)) -> Iterator(a) {
-  fn() { do_append(first.continuation, second.continuation) }
+  fn() { append_loop(first.continuation, second.continuation) }
   |> Iterator
 }
 
-fn do_flatten(flattened: fn() -> Action(Iterator(a))) -> Action(a) {
-  case flattened() {
-    Stop -> Stop
-    Continue(it, next_iterator) ->
-      do_append(it.continuation, fn() { do_flatten(next_iterator) })
+fn append_loop(first: fn() -> Action(a), second: fn() -> Action(a)) -> Action(a) {
+  case first() {
+    Continue(e, first) -> Continue(e, fn() { append_loop(first, second) })
+    Stop -> second()
   }
 }
 
@@ -482,10 +474,18 @@ fn do_flatten(flattened: fn() -> Action(Iterator(a))) -> Action(a) {
 /// ```
 ///
 pub fn flatten(iterator: Iterator(Iterator(a))) -> Iterator(a) {
-  fn() { do_flatten(iterator.continuation) }
+  fn() { flatten_loop(iterator.continuation) }
   |> Iterator
 }
 
+fn flatten_loop(flattened: fn() -> Action(Iterator(a))) -> Action(a) {
+  case flattened() {
+    Stop -> Stop
+    Continue(it, next_iterator) ->
+      append_loop(it.continuation, fn() { flatten_loop(next_iterator) })
+  }
+}
+
 /// Joins a list of iterators into a single iterator.
 ///
 /// This function does not evaluate the elements of the iterator, the
@@ -532,20 +532,6 @@ pub fn flat_map(
   |> flatten
 }
 
-fn do_filter(
-  continuation: fn() -> Action(e),
-  predicate: fn(e) -> Bool,
-) -> Action(e) {
-  case continuation() {
-    Stop -> Stop
-    Continue(e, iterator) ->
-      case predicate(e) {
-        True -> Continue(e, fn() { do_filter(iterator, predicate) })
-        False -> do_filter(iterator, predicate)
-      }
-  }
-}
-
 /// Creates an iterator from an existing iterator and a predicate function.
 ///
 /// The new iterator will contain elements from the first iterator for which
@@ -569,20 +555,20 @@ pub fn filter(
   iterator: Iterator(a),
   keeping predicate: fn(a) -> Bool,
 ) -> Iterator(a) {
-  fn() { do_filter(iterator.continuation, predicate) }
+  fn() { filter_loop(iterator.continuation, predicate) }
   |> Iterator
 }
 
-fn do_filter_map(
-  continuation: fn() -> Action(a),
-  f: fn(a) -> Result(b, c),
-) -> Action(b) {
+fn filter_loop(
+  continuation: fn() -> Action(e),
+  predicate: fn(e) -> Bool,
+) -> Action(e) {
   case continuation() {
     Stop -> Stop
-    Continue(e, next) ->
-      case f(e) {
-        Ok(e) -> Continue(e, fn() { do_filter_map(next, f) })
-        Error(_) -> do_filter_map(next, f)
+    Continue(e, iterator) ->
+      case predicate(e) {
+        True -> Continue(e, fn() { filter_loop(iterator, predicate) })
+        False -> filter_loop(iterator, predicate)
       }
   }
 }
@@ -613,10 +599,24 @@ pub fn filter_map(
   iterator: Iterator(a),
   keeping_with f: fn(a) -> Result(b, c),
 ) -> Iterator(b) {
-  fn() { do_filter_map(iterator.continuation, f) }
+  fn() { filter_map_loop(iterator.continuation, f) }
   |> Iterator
 }
 
+fn filter_map_loop(
+  continuation: fn() -> Action(a),
+  f: fn(a) -> Result(b, c),
+) -> Action(b) {
+  case continuation() {
+    Stop -> Stop
+    Continue(e, next) ->
+      case f(e) {
+        Ok(e) -> Continue(e, fn() { filter_map_loop(next, f) })
+        Error(_) -> filter_map_loop(next, f)
+      }
+  }
+}
+
 /// Creates an iterator that repeats a given iterator infinitely.
 ///
 /// ## Examples
@@ -675,17 +675,6 @@ pub fn range(from start: Int, to stop: Int) -> Iterator(Int) {
   }
 }
 
-fn do_find(continuation: fn() -> Action(a), f: fn(a) -> Bool) -> Result(a, Nil) {
-  case continuation() {
-    Stop -> Error(Nil)
-    Continue(e, next) ->
-      case f(e) {
-        True -> Ok(e)
-        False -> do_find(next, f)
-      }
-  }
-}
-
 /// Finds the first element in a given iterator for which the given function returns
 /// `True`.
 ///
@@ -714,19 +703,19 @@ pub fn find(
   one_that is_desired: fn(a) -> Bool,
 ) -> Result(a, Nil) {
   haystack.continuation
-  |> do_find(is_desired)
+  |> find_loop(is_desired)
 }
 
-fn do_find_map(
+fn find_loop(
   continuation: fn() -> Action(a),
-  f: fn(a) -> Result(b, c),
-) -> Result(b, Nil) {
+  f: fn(a) -> Bool,
+) -> Result(a, Nil) {
   case continuation() {
     Stop -> Error(Nil)
     Continue(e, next) ->
       case f(e) {
-        Ok(e) -> Ok(e)
-        Error(_) -> do_find_map(next, f)
+        True -> Ok(e)
+        False -> find_loop(next, f)
       }
   }
 }
@@ -759,19 +748,20 @@ pub fn find_map(
   one_that is_desired: fn(a) -> Result(b, c),
 ) -> Result(b, Nil) {
   haystack.continuation
-  |> do_find_map(is_desired)
+  |> find_map_loop(is_desired)
 }
 
-fn do_index(
-  continuation: fn() -> Action(element),
-  next: Int,
-) -> fn() -> Action(#(element, Int)) {
-  fn() {
-    case continuation() {
-      Stop -> Stop
-      Continue(e, continuation) ->
-        Continue(#(e, next), do_index(continuation, next + 1))
-    }
+fn find_map_loop(
+  continuation: fn() -> Action(a),
+  f: fn(a) -> Result(b, c),
+) -> Result(b, Nil) {
+  case continuation() {
+    Stop -> Error(Nil)
+    Continue(e, next) ->
+      case f(e) {
+        Ok(e) -> Ok(e)
+        Error(_) -> find_map_loop(next, f)
+      }
   }
 }
 
@@ -786,10 +776,23 @@ fn do_index(
 ///
 pub fn index(over iterator: Iterator(element)) -> Iterator(#(element, Int)) {
   iterator.continuation
-  |> do_index(0)
+  |> index_loop(0)
   |> Iterator
 }
 
+fn index_loop(
+  continuation: fn() -> Action(element),
+  next: Int,
+) -> fn() -> Action(#(element, Int)) {
+  fn() {
+    case continuation() {
+      Stop -> Stop
+      Continue(e, continuation) ->
+        Continue(#(e, next), index_loop(continuation, next + 1))
+    }
+  }
+}
+
 /// Creates an iterator that infinitely applies a function to a value.
 ///
 /// ## Examples
@@ -806,22 +809,6 @@ pub fn iterate(
   unfold(initial, fn(element) { Next(element, f(element)) })
 }
 
-fn do_take_while(
-  continuation: fn() -> Action(element),
-  predicate: fn(element) -> Bool,
-) -> fn() -> Action(element) {
-  fn() {
-    case continuation() {
-      Stop -> Stop
-      Continue(e, next) ->
-        case predicate(e) {
-          False -> Stop
-          True -> Continue(e, do_take_while(next, predicate))
-        }
-    }
-  }
-}
-
 /// Creates an iterator that yields elements while the predicate returns `True`.
 ///
 /// ## Examples
@@ -838,21 +825,23 @@ pub fn take_while(
   satisfying predicate: fn(element) -> Bool,
 ) -> Iterator(element) {
   iterator.continuation
-  |> do_take_while(predicate)
+  |> take_while_loop(predicate)
   |> Iterator
 }
 
-fn do_drop_while(
+fn take_while_loop(
   continuation: fn() -> Action(element),
   predicate: fn(element) -> Bool,
-) -> Action(element) {
-  case continuation() {
-    Stop -> Stop
-    Continue(e, next) ->
-      case predicate(e) {
-        False -> Continue(e, next)
-        True -> do_drop_while(next, predicate)
-      }
+) -> fn() -> Action(element) {
+  fn() {
+    case continuation() {
+      Stop -> Stop
+      Continue(e, next) ->
+        case predicate(e) {
+          False -> Stop
+          True -> Continue(e, take_while_loop(next, predicate))
+        }
+    }
   }
 }
 
@@ -872,23 +861,21 @@ pub fn drop_while(
   in iterator: Iterator(element),
   satisfying predicate: fn(element) -> Bool,
 ) -> Iterator(element) {
-  fn() { do_drop_while(iterator.continuation, predicate) }
+  fn() { drop_while_loop(iterator.continuation, predicate) }
   |> Iterator
 }
 
-fn do_scan(
+fn drop_while_loop(
   continuation: fn() -> Action(element),
-  f: fn(acc, element) -> acc,
-  accumulator: acc,
-) -> fn() -> Action(acc) {
-  fn() {
-    case continuation() {
-      Stop -> Stop
-      Continue(el, next) -> {
-        let accumulated = f(accumulator, el)
-        Continue(accumulated, do_scan(next, f, accumulated))
+  predicate: fn(element) -> Bool,
+) -> Action(element) {
+  case continuation() {
+    Stop -> Stop
+    Continue(e, next) ->
+      case predicate(e) {
+        False -> Continue(e, next)
+        True -> drop_while_loop(next, predicate)
       }
-    }
   }
 }
 
@@ -912,23 +899,22 @@ pub fn scan(
   with f: fn(acc, element) -> acc,
 ) -> Iterator(acc) {
   iterator.continuation
-  |> do_scan(f, initial)
+  |> scan_loop(f, initial)
   |> Iterator
 }
 
-fn do_zip(
-  left: fn() -> Action(a),
-  right: fn() -> Action(b),
-) -> fn() -> Action(#(a, b)) {
+fn scan_loop(
+  continuation: fn() -> Action(element),
+  f: fn(acc, element) -> acc,
+  accumulator: acc,
+) -> fn() -> Action(acc) {
   fn() {
-    case left() {
+    case continuation() {
       Stop -> Stop
-      Continue(el_left, next_left) ->
-        case right() {
-          Stop -> Stop
-          Continue(el_right, next_right) ->
-            Continue(#(el_left, el_right), do_zip(next_left, next_right))
-        }
+      Continue(el, next) -> {
+        let accumulated = f(accumulator, el)
+        Continue(accumulated, scan_loop(next, f, accumulated))
+      }
     }
   }
 }
@@ -946,45 +932,31 @@ fn do_zip(
 /// ```
 ///
 pub fn zip(left: Iterator(a), right: Iterator(b)) -> Iterator(#(a, b)) {
-  do_zip(left.continuation, right.continuation)
+  zip_loop(left.continuation, right.continuation)
   |> Iterator
 }
 
-// Result of collecting a single chunk by key
-type Chunk(element, key) {
-  AnotherBy(List(element), key, element, fn() -> Action(element))
-  LastBy(List(element))
-}
-
-fn next_chunk(
-  continuation: fn() -> Action(element),
-  f: fn(element) -> key,
-  previous_key: key,
-  current_chunk: List(element),
-) -> Chunk(element, key) {
-  case continuation() {
-    Stop -> LastBy(list.reverse(current_chunk))
-    Continue(e, next) -> {
-      let key = f(e)
-      case key == previous_key {
-        True -> next_chunk(next, f, key, [e, ..current_chunk])
-        False -> AnotherBy(list.reverse(current_chunk), key, e, next)
-      }
+fn zip_loop(
+  left: fn() -> Action(a),
+  right: fn() -> Action(b),
+) -> fn() -> Action(#(a, b)) {
+  fn() {
+    case left() {
+      Stop -> Stop
+      Continue(el_left, next_left) ->
+        case right() {
+          Stop -> Stop
+          Continue(el_right, next_right) ->
+            Continue(#(el_left, el_right), zip_loop(next_left, next_right))
+        }
     }
   }
 }
 
-fn do_chunk(
-  continuation: fn() -> Action(element),
-  f: fn(element) -> key,
-  previous_key: key,
-  previous_element: element,
-) -> Action(List(element)) {
-  case next_chunk(continuation, f, previous_key, [previous_element]) {
-    LastBy(chunk) -> Continue(chunk, stop)
-    AnotherBy(chunk, key, el, next) ->
-      Continue(chunk, fn() { do_chunk(next, f, key, el) })
-  }
+// Result of collecting a single chunk by key
+type Chunk(element, key) {
+  AnotherBy(List(element), key, element, fn() -> Action(element))
+  LastBy(List(element))
 }
 
 /// Creates an iterator that emits chunks of elements
@@ -1006,54 +978,43 @@ pub fn chunk(
   fn() {
     case iterator.continuation() {
       Stop -> Stop
-      Continue(e, next) -> do_chunk(next, f, f(e), e)
+      Continue(e, next) -> chunk_loop(next, f, f(e), e)
     }
   }
   |> Iterator
 }
 
-// Result of collecting a single sized chunk
-type SizedChunk(element) {
-  Another(List(element), fn() -> Action(element))
-  Last(List(element))
-  NoMore
+fn chunk_loop(
+  continuation: fn() -> Action(element),
+  f: fn(element) -> key,
+  previous_key: key,
+  previous_element: element,
+) -> Action(List(element)) {
+  case next_chunk(continuation, f, previous_key, [previous_element]) {
+    LastBy(chunk) -> Continue(chunk, stop)
+    AnotherBy(chunk, key, el, next) ->
+      Continue(chunk, fn() { chunk_loop(next, f, key, el) })
+  }
 }
 
-fn next_sized_chunk(
+fn next_chunk(
   continuation: fn() -> Action(element),
-  left: Int,
+  f: fn(element) -> key,
+  previous_key: key,
   current_chunk: List(element),
-) -> SizedChunk(element) {
+) -> Chunk(element, key) {
   case continuation() {
-    Stop ->
-      case current_chunk {
-        [] -> NoMore
-        remaining -> Last(list.reverse(remaining))
-      }
+    Stop -> LastBy(list.reverse(current_chunk))
     Continue(e, next) -> {
-      let chunk = [e, ..current_chunk]
-      case left > 1 {
-        False -> Another(list.reverse(chunk), next)
-        True -> next_sized_chunk(next, left - 1, chunk)
+      let key = f(e)
+      case key == previous_key {
+        True -> next_chunk(next, f, key, [e, ..current_chunk])
+        False -> AnotherBy(list.reverse(current_chunk), key, e, next)
       }
     }
   }
 }
 
-fn do_sized_chunk(
-  continuation: fn() -> Action(element),
-  count: Int,
-) -> fn() -> Action(List(element)) {
-  fn() {
-    case next_sized_chunk(continuation, count, []) {
-      NoMore -> Stop
-      Last(chunk) -> Continue(chunk, stop)
-      Another(chunk, next_element) ->
-        Continue(chunk, do_sized_chunk(next_element, count))
-    }
-  }
-}
-
 /// Creates an iterator that emits chunks of given size.
 ///
 /// If the last chunk does not have `count` elements, it is yielded
@@ -1082,19 +1043,48 @@ pub fn sized_chunk(
   into count: Int,
 ) -> Iterator(List(element)) {
   iterator.continuation
-  |> do_sized_chunk(count)
+  |> sized_chunk_loop(count)
   |> Iterator
 }
 
-fn do_intersperse(
+fn sized_chunk_loop(
   continuation: fn() -> Action(element),
-  separator: element,
-) -> Action(element) {
+  count: Int,
+) -> fn() -> Action(List(element)) {
+  fn() {
+    case next_sized_chunk(continuation, count, []) {
+      NoMore -> Stop
+      Last(chunk) -> Continue(chunk, stop)
+      Another(chunk, next_element) ->
+        Continue(chunk, sized_chunk_loop(next_element, count))
+    }
+  }
+}
+
+// Result of collecting a single sized chunk
+type SizedChunk(element) {
+  Another(List(element), fn() -> Action(element))
+  Last(List(element))
+  NoMore
+}
+
+fn next_sized_chunk(
+  continuation: fn() -> Action(element),
+  left: Int,
+  current_chunk: List(element),
+) -> SizedChunk(element) {
   case continuation() {
-    Stop -> Stop
+    Stop ->
+      case current_chunk {
+        [] -> NoMore
+        remaining -> Last(list.reverse(remaining))
+      }
     Continue(e, next) -> {
-      let next_interspersed = fn() { do_intersperse(next, separator) }
-      Continue(separator, fn() { Continue(e, next_interspersed) })
+      let chunk = [e, ..current_chunk]
+      case left > 1 {
+        False -> Another(list.reverse(chunk), next)
+        True -> next_sized_chunk(next, left - 1, chunk)
+      }
     }
   }
 }
@@ -1132,23 +1122,22 @@ pub fn intersperse(
   fn() {
     case iterator.continuation() {
       Stop -> Stop
-      Continue(e, next) -> Continue(e, fn() { do_intersperse(next, elem) })
+      Continue(e, next) -> Continue(e, fn() { intersperse_loop(next, elem) })
     }
   }
   |> Iterator
 }
 
-fn do_any(
+fn intersperse_loop(
   continuation: fn() -> Action(element),
-  predicate: fn(element) -> Bool,
-) -> Bool {
+  separator: element,
+) -> Action(element) {
   case continuation() {
-    Stop -> False
-    Continue(e, next) ->
-      case predicate(e) {
-        True -> True
-        False -> do_any(next, predicate)
-      }
+    Stop -> Stop
+    Continue(e, next) -> {
+      let next_interspersed = fn() { intersperse_loop(next, separator) }
+      Continue(separator, fn() { Continue(e, next_interspersed) })
+    }
   }
 }
 
@@ -1184,19 +1173,19 @@ pub fn any(
   satisfying predicate: fn(element) -> Bool,
 ) -> Bool {
   iterator.continuation
-  |> do_any(predicate)
+  |> any_loop(predicate)
 }
 
-fn do_all(
+fn any_loop(
   continuation: fn() -> Action(element),
   predicate: fn(element) -> Bool,
 ) -> Bool {
   case continuation() {
-    Stop -> True
+    Stop -> False
     Continue(e, next) ->
       case predicate(e) {
-        True -> do_all(next, predicate)
-        False -> False
+        True -> True
+        False -> any_loop(next, predicate)
       }
   }
 }
@@ -1233,24 +1222,20 @@ pub fn all(
   satisfying predicate: fn(element) -> Bool,
 ) -> Bool {
   iterator.continuation
-  |> do_all(predicate)
-}
-
-fn update_group_with(el: element) -> fn(Option(List(element))) -> List(element) {
-  fn(maybe_group) {
-    case maybe_group {
-      Some(group) -> [el, ..group]
-      None -> [el]
-    }
-  }
+  |> all_loop(predicate)
 }
 
-fn group_updater(
-  f: fn(element) -> key,
-) -> fn(Dict(key, List(element)), element) -> Dict(key, List(element)) {
-  fn(groups, elem) {
-    groups
-    |> dict.upsert(f(elem), update_group_with(elem))
+fn all_loop(
+  continuation: fn() -> Action(element),
+  predicate: fn(element) -> Bool,
+) -> Bool {
+  case continuation() {
+    Stop -> True
+    Continue(e, next) ->
+      case predicate(e) {
+        True -> all_loop(next, predicate)
+        False -> False
+      }
   }
 }
 
@@ -1276,6 +1261,24 @@ pub fn group(
   |> dict.map_values(fn(_, group) { list.reverse(group) })
 }
 
+fn group_updater(
+  f: fn(element) -> key,
+) -> fn(Dict(key, List(element)), element) -> Dict(key, List(element)) {
+  fn(groups, elem) {
+    groups
+    |> dict.upsert(f(elem), update_group_with(elem))
+  }
+}
+
+fn update_group_with(el: element) -> fn(Option(List(element))) -> List(element) {
+  fn(maybe_group) {
+    case maybe_group {
+      Some(group) -> [el, ..group]
+      None -> [el]
+    }
+  }
+}
+
 /// This function acts similar to fold, but does not take an initial state.
 /// Instead, it starts from the first yielded element
 /// and combines it with each subsequent element in turn using the given function.
@@ -1304,7 +1307,7 @@ pub fn reduce(
   case iterator.continuation() {
     Stop -> Error(Nil)
     Continue(e, next) ->
-      do_fold(next, f, e)
+      fold_loop(next, f, e)
       |> Ok
   }
 }
@@ -1372,17 +1375,6 @@ pub fn single(elem: element) -> Iterator(element) {
   once(fn() { elem })
 }
 
-fn do_interleave(
-  current: fn() -> Action(element),
-  next: fn() -> Action(element),
-) -> Action(element) {
-  case current() {
-    Stop -> next()
-    Continue(e, next_other) ->
-      Continue(e, fn() { do_interleave(next, next_other) })
-  }
-}
-
 /// Creates an iterator that alternates between the two given iterators
 /// until both have run out.
 ///
@@ -1406,22 +1398,18 @@ pub fn interleave(
   left: Iterator(element),
   with right: Iterator(element),
 ) -> Iterator(element) {
-  fn() { do_interleave(left.continuation, right.continuation) }
+  fn() { interleave_loop(left.continuation, right.continuation) }
   |> Iterator
 }
 
-fn do_fold_until(
-  continuation: fn() -> Action(e),
-  f: fn(acc, e) -> list.ContinueOrStop(acc),
-  accumulator: acc,
-) -> acc {
-  case continuation() {
-    Stop -> accumulator
-    Continue(elem, next) ->
-      case f(accumulator, elem) {
-        list.Continue(accumulator) -> do_fold_until(next, f, accumulator)
-        list.Stop(accumulator) -> accumulator
-      }
+fn interleave_loop(
+  current: fn() -> Action(element),
+  next: fn() -> Action(element),
+) -> Action(element) {
+  case current() {
+    Stop -> next()
+    Continue(e, next_other) ->
+      Continue(e, fn() { interleave_loop(next, next_other) })
   }
 }
 
@@ -1455,22 +1443,21 @@ pub fn fold_until(
   with f: fn(acc, e) -> list.ContinueOrStop(acc),
 ) -> acc {
   iterator.continuation
-  |> do_fold_until(f, initial)
+  |> fold_until_loop(f, initial)
 }
 
-fn do_try_fold(
-  over continuation: fn() -> Action(a),
-  with f: fn(acc, a) -> Result(acc, err),
-  from accumulator: acc,
-) -> Result(acc, err) {
+fn fold_until_loop(
+  continuation: fn() -> Action(e),
+  f: fn(acc, e) -> list.ContinueOrStop(acc),
+  accumulator: acc,
+) -> acc {
   case continuation() {
-    Stop -> Ok(accumulator)
-    Continue(elem, next) -> {
+    Stop -> accumulator
+    Continue(elem, next) ->
       case f(accumulator, elem) {
-        Ok(result) -> do_try_fold(next, f, result)
-        Error(_) as error -> error
+        list.Continue(accumulator) -> fold_until_loop(next, f, accumulator)
+        list.Stop(accumulator) -> accumulator
       }
-    }
   }
 }
 
@@ -1499,7 +1486,23 @@ pub fn try_fold(
   with f: fn(acc, e) -> Result(acc, err),
 ) -> Result(acc, err) {
   iterator.continuation
-  |> do_try_fold(f, initial)
+  |> try_fold_loop(f, initial)
+}
+
+fn try_fold_loop(
+  over continuation: fn() -> Action(a),
+  with f: fn(acc, a) -> Result(acc, err),
+  from accumulator: acc,
+) -> Result(acc, err) {
+  case continuation() {
+    Stop -> Ok(accumulator)
+    Continue(elem, next) -> {
+      case f(accumulator, elem) {
+        Ok(result) -> try_fold_loop(next, f, result)
+        Error(_) as error -> error
+      }
+    }
+  }
 }
 
 /// Returns the first element yielded by the given iterator, if it exists,
@@ -1552,13 +1555,6 @@ pub fn at(in iterator: Iterator(e), get index: Int) -> Result(e, Nil) {
   |> first
 }
 
-fn do_length(over continuation: fn() -> Action(e), with length: Int) -> Int {
-  case continuation() {
-    Stop -> length
-    Continue(_, next) -> do_length(next, length + 1)
-  }
-}
-
 /// Counts the number of elements in the given iterator.
 ///
 /// This function has to traverse the entire iterator to count its elements,
@@ -1578,7 +1574,14 @@ fn do_length(over continuation: fn() -> Action(e), with length: Int) -> Int {
 ///
 pub fn length(over iterator: Iterator(e)) -> Int {
   iterator.continuation
-  |> do_length(0)
+  |> length_loop(0)
+}
+
+fn length_loop(over continuation: fn() -> Action(e), with length: Int) -> Int {
+  case continuation() {
+    Stop -> length
+    Continue(_, next) -> length_loop(next, length + 1)
+  }
 }
 
 /// Traverse an iterator, calling a function on each element.
diff --git a/src/gleam/list.gleam b/src/gleam/list.gleam
index c363cda..97084db 100644
--- a/src/gleam/list.gleam
+++ b/src/gleam/list.gleam
@@ -124,13 +124,13 @@ pub fn count(list: List(a), where predicate: fn(a) -> Bool) -> Int {
 ///
 @external(erlang, "lists", "reverse")
 pub fn reverse(list: List(a)) -> List(a) {
-  do_reverse(list, [])
+  reverse_loop(list, [])
 }
 
-fn do_reverse(remaining: List(a), accumulator: List(a)) -> List(a) {
+fn reverse_loop(remaining: List(a), accumulator: List(a)) -> List(a) {
   case remaining {
     [] -> accumulator
-    [item, ..rest] -> do_reverse(rest, [item, ..accumulator])
+    [item, ..rest] -> reverse_loop(rest, [item, ..accumulator])
   }
 }
 
@@ -299,19 +299,6 @@ pub fn group(list: List(v), by key: fn(v) -> k) -> Dict(k, List(v)) {
   fold(list, dict.new(), update_group(key))
 }
 
-fn do_filter(list: List(a), fun: fn(a) -> Bool, acc: List(a)) -> List(a) {
-  case list {
-    [] -> reverse(acc)
-    [first, ..rest] -> {
-      let new_acc = case fun(first) {
-        True -> [first, ..acc]
-        False -> acc
-      }
-      do_filter(rest, fun, new_acc)
-    }
-  }
-}
-
 /// Returns a new list containing only the elements from the first list for
 /// which the given functions returns `True`.
 ///
@@ -328,22 +315,18 @@ fn do_filter(list: List(a), fun: fn(a) -> Bool, acc: List(a)) -> List(a) {
 /// ```
 ///
 pub fn filter(list: List(a), keeping predicate: fn(a) -> Bool) -> List(a) {
-  do_filter(list, predicate, [])
+  filter_loop(list, predicate, [])
 }
 
-fn do_filter_map(
-  list: List(a),
-  fun: fn(a) -> Result(b, e),
-  acc: List(b),
-) -> List(b) {
+fn filter_loop(list: List(a), fun: fn(a) -> Bool, acc: List(a)) -> List(a) {
   case list {
     [] -> reverse(acc)
     [first, ..rest] -> {
       let new_acc = case fun(first) {
-        Ok(first) -> [first, ..acc]
-        Error(_) -> acc
+        True -> [first, ..acc]
+        False -> acc
       }
-      do_filter_map(rest, fun, new_acc)
+      filter_loop(rest, fun, new_acc)
     }
   }
 }
@@ -364,13 +347,23 @@ fn do_filter_map(
 /// ```
 ///
 pub fn filter_map(list: List(a), with fun: fn(a) -> Result(b, e)) -> List(b) {
-  do_filter_map(list, fun, [])
+  filter_map_loop(list, fun, [])
 }
 
-fn do_map(list: List(a), fun: fn(a) -> b, acc: List(b)) -> List(b) {
+fn filter_map_loop(
+  list: List(a),
+  fun: fn(a) -> Result(b, e),
+  acc: List(b),
+) -> List(b) {
   case list {
     [] -> reverse(acc)
-    [first, ..rest] -> do_map(rest, fun, [fun(first), ..acc])
+    [first, ..rest] -> {
+      let new_acc = case fun(first) {
+        Ok(first) -> [first, ..acc]
+        Error(_) -> acc
+      }
+      filter_map_loop(rest, fun, new_acc)
+    }
   }
 }
 
@@ -385,7 +378,14 @@ fn do_map(list: List(a), fun: fn(a) -> b, acc: List(b)) -> List(b) {
 /// ```
 ///
 pub fn map(list: List(a), with fun: fn(a) -> b) -> List(b) {
-  do_map(list, fun, [])
+  map_loop(list, fun, [])
+}
+
+fn map_loop(list: List(a), fun: fn(a) -> b, acc: List(b)) -> List(b) {
+  case list {
+    [] -> reverse(acc)
+    [first, ..rest] -> map_loop(rest, fun, [fun(first), ..acc])
+  }
 }
 
 /// Combines two lists into a single list using the given function.
@@ -405,10 +405,10 @@ pub fn map(list: List(a), with fun: fn(a) -> b) -> List(b) {
 /// ```
 ///
 pub fn map2(list1: List(a), list2: List(b), with fun: fn(a, b) -> c) -> List(c) {
-  do_map2(list1, list2, fun, [])
+  map2_loop(list1, list2, fun, [])
 }
 
-fn do_map2(
+fn map2_loop(
   list1: List(a),
   list2: List(b),
   fun: fn(a, b) -> c,
@@ -416,7 +416,7 @@ fn do_map2(
 ) -> List(c) {
   case list1, list2 {
     [], _ | _, [] -> reverse(acc)
-    [a, ..as_], [b, ..bs] -> do_map2(as_, bs, fun, [fun(a, b), ..acc])
+    [a, ..as_], [b, ..bs] -> map2_loop(as_, bs, fun, [fun(a, b), ..acc])
   }
 }
 
@@ -446,21 +446,6 @@ pub fn map_fold(
   |> pair.map_second(reverse)
 }
 
-fn do_index_map(
-  list: List(a),
-  fun: fn(a, Int) -> b,
-  index: Int,
-  acc: List(b),
-) -> List(b) {
-  case list {
-    [] -> reverse(acc)
-    [first, ..rest] -> {
-      let acc = [fun(first, index), ..acc]
-      do_index_map(rest, fun, index + 1, acc)
-    }
-  }
-}
-
 /// Returns a new list containing only the elements of the first list after the
 /// function has been applied to each one and their index.
 ///
@@ -475,21 +460,21 @@ fn do_index_map(
 /// ```
 ///
 pub fn index_map(list: List(a), with fun: fn(a, Int) -> b) -> List(b) {
-  do_index_map(list, fun, 0, [])
+  index_map_loop(list, fun, 0, [])
 }
 
-fn do_try_map(
+fn index_map_loop(
   list: List(a),
-  fun: fn(a) -> Result(b, e),
+  fun: fn(a, Int) -> b,
+  index: Int,
   acc: List(b),
-) -> Result(List(b), e) {
+) -> List(b) {
   case list {
-    [] -> Ok(reverse(acc))
-    [first, ..rest] ->
-      case fun(first) {
-        Ok(first) -> do_try_map(rest, fun, [first, ..acc])
-        Error(error) -> Error(error)
-      }
+    [] -> reverse(acc)
+    [first, ..rest] -> {
+      let acc = [fun(first, index), ..acc]
+      index_map_loop(rest, fun, index + 1, acc)
+    }
   }
 }
 
@@ -529,7 +514,22 @@ pub fn try_map(
   over list: List(a),
   with fun: fn(a) -> Result(b, e),
 ) -> Result(List(b), e) {
-  do_try_map(list, fun, [])
+  try_map_loop(list, fun, [])
+}
+
+fn try_map_loop(
+  list: List(a),
+  fun: fn(a) -> Result(b, e),
+  acc: List(b),
+) -> Result(List(b), e) {
+  case list {
+    [] -> Ok(reverse(acc))
+    [first, ..rest] ->
+      case fun(first) {
+        Ok(first) -> try_map_loop(rest, fun, [first, ..acc])
+        Error(error) -> Error(error)
+      }
+  }
 }
 
 /// Returns a list that is the given list with up to the given number of
@@ -563,17 +563,6 @@ pub fn drop(from list: List(a), up_to n: Int) -> List(a) {
   }
 }
 
-fn do_take(list: List(a), n: Int, acc: List(a)) -> List(a) {
-  case n <= 0 {
-    True -> reverse(acc)
-    False ->
-      case list {
-        [] -> reverse(acc)
-        [first, ..rest] -> do_take(rest, n - 1, [first, ..acc])
-      }
-  }
-}
-
 /// Returns a list containing the first given number of elements from the given
 /// list.
 ///
@@ -595,7 +584,18 @@ fn do_take(list: List(a), n: Int, acc: List(a)) -> List(a) {
 /// ```
 ///
 pub fn take(from list: List(a), up_to n: Int) -> List(a) {
-  do_take(list, n, [])
+  take_loop(list, n, [])
+}
+
+fn take_loop(list: List(a), n: Int, acc: List(a)) -> List(a) {
+  case n <= 0 {
+    True -> reverse(acc)
+    False ->
+      case list {
+        [] -> reverse(acc)
+        [first, ..rest] -> take_loop(rest, n - 1, [first, ..acc])
+      }
+  }
 }
 
 /// Returns a new empty list.
@@ -645,13 +645,13 @@ pub fn wrap(item: a) -> List(a) {
 ///
 @external(erlang, "lists", "append")
 pub fn append(first: List(a), second: List(a)) -> List(a) {
-  do_append(reverse(first), second)
+  append_loop(reverse(first), second)
 }
 
-fn do_append(first: List(a), second: List(a)) -> List(a) {
+fn append_loop(first: List(a), second: List(a)) -> List(a) {
   case first {
     [] -> second
-    [item, ..rest] -> do_append(rest, [item, ..second])
+    [item, ..rest] -> append_loop(rest, [item, ..second])
   }
 }
 
@@ -680,14 +680,6 @@ fn reverse_and_prepend(list prefix: List(a), to suffix: List(a)) -> List(a) {
   }
 }
 
-fn do_concat(lists: List(List(a)), acc: List(a)) -> List(a) {
-  case lists {
-    [] -> reverse(acc)
-    [list, ..further_lists] ->
-      do_concat(further_lists, reverse_and_prepend(list: list, to: acc))
-  }
-}
-
 /// Joins a list of lists into a single list.
 ///
 /// This function traverses all elements twice.
@@ -701,7 +693,15 @@ fn do_concat(lists: List(List(a)), acc: List(a)) -> List(a) {
 ///
 @deprecated("Use `list.flatten` instead.")
 pub fn concat(lists: List(List(a))) -> List(a) {
-  do_concat(lists, [])
+  concat_loop(lists, [])
+}
+
+fn concat_loop(lists: List(List(a)), acc: List(a)) -> List(a) {
+  case lists {
+    [] -> reverse(acc)
+    [list, ..further_lists] ->
+      concat_loop(further_lists, reverse_and_prepend(list: list, to: acc))
+  }
 }
 
 /// This is the same as `concat`: it joins a list of lists into a single
@@ -717,7 +717,7 @@ pub fn concat(lists: List(List(a))) -> List(a) {
 /// ```
 ///
 pub fn flatten(lists: List(List(a))) -> List(a) {
-  do_concat(lists, [])
+  concat_loop(lists, [])
 }
 
 /// Maps the list with the given function into a list of lists, and then flattens it.
@@ -775,19 +775,6 @@ pub fn fold_right(
   }
 }
 
-fn do_index_fold(
-  over: List(a),
-  acc: acc,
-  with: fn(acc, a, Int) -> acc,
-  index: Int,
-) -> acc {
-  case over {
-    [] -> acc
-    [first, ..rest] ->
-      do_index_fold(rest, with(acc, first, index), with, index + 1)
-  }
-}
-
 /// Like fold but the folding function also receives the index of the current element.
 ///
 /// ## Examples
@@ -802,7 +789,20 @@ pub fn index_fold(
   from initial: acc,
   with fun: fn(acc, a, Int) -> acc,
 ) -> acc {
-  do_index_fold(list, initial, fun, 0)
+  index_fold_loop(list, initial, fun, 0)
+}
+
+fn index_fold_loop(
+  over: List(a),
+  acc: acc,
+  with: fn(acc, a, Int) -> acc,
+  index: Int,
+) -> acc {
+  case over {
+    [] -> acc
+    [first, ..rest] ->
+      index_fold_loop(rest, with(acc, first, index), with, index + 1)
+  }
 }
 
 /// A variant of fold that might fail.
@@ -1019,14 +1019,6 @@ pub fn any(in list: List(a), satisfying predicate: fn(a) -> Bool) -> Bool {
   }
 }
 
-fn do_zip(one: List(a), other: List(b), acc: List(#(a, b))) -> List(#(a, b)) {
-  case one, other {
-    [first_one, ..rest_one], [first_other, ..rest_other] ->
-      do_zip(rest_one, rest_other, [#(first_one, first_other), ..acc])
-    _, _ -> reverse(acc)
-  }
-}
-
 /// Takes two lists and returns a single list of 2-element tuples.
 ///
 /// If one of the lists is longer than the other, the remaining elements from
@@ -1055,7 +1047,15 @@ fn do_zip(one: List(a), other: List(b), acc: List(#(a, b))) -> List(#(a, b)) {
 /// ```
 ///
 pub fn zip(list: List(a), with other: List(b)) -> List(#(a, b)) {
-  do_zip(list, other, [])
+  zip_loop(list, other, [])
+}
+
+fn zip_loop(one: List(a), other: List(b), acc: List(#(a, b))) -> List(#(a, b)) {
+  case one, other {
+    [first_one, ..rest_one], [first_other, ..rest_other] ->
+      zip_loop(rest_one, rest_other, [#(first_one, first_other), ..acc])
+    _, _ -> reverse(acc)
+  }
 }
 
 /// Takes two lists and returns a single list of 2-element tuples.
@@ -1094,18 +1094,6 @@ pub fn strict_zip(
   }
 }
 
-fn do_unzip(
-  input: List(#(a, b)),
-  one: List(a),
-  other: List(b),
-) -> #(List(a), List(b)) {
-  case input {
-    [] -> #(reverse(one), reverse(other))
-    [#(first_one, first_other), ..rest] ->
-      do_unzip(rest, [first_one, ..one], [first_other, ..other])
-  }
-}
-
 /// Takes a single list of 2-element tuples and returns two lists.
 ///
 /// ## Examples
@@ -1121,13 +1109,18 @@ fn do_unzip(
 /// ```
 ///
 pub fn unzip(input: List(#(a, b))) -> #(List(a), List(b)) {
-  do_unzip(input, [], [])
+  unzip_loop(input, [], [])
 }
 
-fn do_intersperse(list: List(a), separator: a, acc: List(a)) -> List(a) {
-  case list {
-    [] -> reverse(acc)
-    [x, ..rest] -> do_intersperse(rest, separator, [x, separator, ..acc])
+fn unzip_loop(
+  input: List(#(a, b)),
+  one: List(a),
+  other: List(b),
+) -> #(List(a), List(b)) {
+  case input {
+    [] -> #(reverse(one), reverse(other))
+    [#(first_one, first_other), ..rest] ->
+      unzip_loop(rest, [first_one, ..one], [first_other, ..other])
   }
 }
 
@@ -1150,7 +1143,14 @@ fn do_intersperse(list: List(a), separator: a, acc: List(a)) -> List(a) {
 pub fn intersperse(list: List(a), with elem: a) -> List(a) {
   case list {
     [] | [_] -> list
-    [x, ..rest] -> do_intersperse(rest, elem, [x])
+    [x, ..rest] -> intersperse_loop(rest, elem, [x])
+  }
+}
+
+fn intersperse_loop(list: List(a), separator: a, acc: List(a)) -> List(a) {
+  case list {
+    [] -> reverse(acc)
+    [x, ..rest] -> intersperse_loop(rest, separator, [x, separator, ..acc])
   }
 }
 
@@ -1264,7 +1264,7 @@ fn sequences(
         // Notice how we have to reverse the accumulator we're growing: since
         // we always add items to the head, `growing` is built in the opposite
         // sorting order of what it actually is in the original list.
-        Ascending -> [do_reverse(growing, []), ..acc]
+        Ascending -> [reverse_loop(growing, []), ..acc]
         Descending -> [growing, ..acc]
       }
 
@@ -1285,7 +1285,7 @@ fn sequences(
         // be the one we just found.
         order.Gt, Ascending | order.Lt, Descending | order.Eq, Descending -> {
           let acc = case direction {
-            Ascending -> [do_reverse(growing, []), ..acc]
+            Ascending -> [reverse_loop(growing, []), ..acc]
             Descending -> [growing, ..acc]
           }
           case rest {
@@ -1326,7 +1326,7 @@ fn merge_all(
 
     // If we have a single list in descending order, we reverse it to make sure
     // it's in ascending order and we're done.
-    [sequence], Descending -> do_reverse(sequence, [])
+    [sequence], Descending -> reverse_loop(sequence, [])
 
     // Merging together sequences that are in ascending (descending) order
     // reverses their order, so the recursive call will assume to be merging
@@ -1353,12 +1353,12 @@ fn merge_ascending_pairs(
   acc: List(List(a)),
 ) {
   case sequences {
-    [] -> do_reverse(acc, [])
+    [] -> reverse_loop(acc, [])
 
     // Beware, if we have just one item left we must reverse it: we take
     // ascending lists as input and have to return descending ones.
     // If we returned it like it is it would be sorted in ascending order.
-    [sequence] -> do_reverse([do_reverse(sequence, []), ..acc], [])
+    [sequence] -> reverse_loop([reverse_loop(sequence, []), ..acc], [])
 
     [ascending1, ascending2, ..rest] -> {
       let descending = merge_ascendings(ascending1, ascending2, compare, [])
@@ -1375,9 +1375,9 @@ fn merge_descending_pairs(
   acc: List(List(a)),
 ) {
   case sequences {
-    [] -> do_reverse(acc, [])
+    [] -> reverse_loop(acc, [])
 
-    [sequence] -> do_reverse([do_reverse(sequence, []), ..acc], [])
+    [sequence] -> reverse_loop([reverse_loop(sequence, []), ..acc], [])
 
     [descending1, descending2, ..rest] -> {
       let ascending = merge_descendings(descending1, descending2, compare, [])
@@ -1401,7 +1401,7 @@ fn merge_ascendings(
   acc: List(a),
 ) -> List(a) {
   case list1, list2 {
-    [], list | list, [] -> do_reverse(list, acc)
+    [], list | list, [] -> reverse_loop(list, acc)
 
     [first1, ..rest1], [first2, ..rest2] ->
       case compare(first1, first2) {
@@ -1428,7 +1428,7 @@ fn merge_descendings(
   acc: List(a),
 ) -> List(a) {
   case list1, list2 {
-    [], list | list, [] -> do_reverse(list, acc)
+    [], list | list, [] -> reverse_loop(list, acc)
     [first1, ..rest1], [first2, ..rest2] ->
       case compare(first1, first2) {
         order.Lt -> merge_descendings(list1, rest2, compare, [first2, ..acc])
@@ -1458,21 +1458,14 @@ fn merge_descendings(
 /// ```
 ///
 pub fn range(from start: Int, to stop: Int) -> List(Int) {
-  tail_recursive_range(start, stop, [])
+  range_loop(start, stop, [])
 }
 
-fn tail_recursive_range(start: Int, stop: Int, acc: List(Int)) -> List(Int) {
+fn range_loop(start: Int, stop: Int, acc: List(Int)) -> List(Int) {
   case int.compare(start, stop) {
     order.Eq -> [stop, ..acc]
-    order.Gt -> tail_recursive_range(start, stop + 1, [stop, ..acc])
-    order.Lt -> tail_recursive_range(start, stop - 1, [stop, ..acc])
-  }
-}
-
-fn do_repeat(item: a, times: Int, acc: List(a)) -> List(a) {
-  case times <= 0 {
-    True -> acc
-    False -> do_repeat(item, times - 1, [item, ..acc])
+    order.Gt -> range_loop(start, stop + 1, [stop, ..acc])
+    order.Lt -> range_loop(start, stop - 1, [stop, ..acc])
   }
 }
 
@@ -1491,17 +1484,13 @@ fn do_repeat(item: a, times: Int, acc: List(a)) -> List(a) {
 /// ```
 ///
 pub fn repeat(item a: a, times times: Int) -> List(a) {
-  do_repeat(a, times, [])
+  repeat_loop(a, times, [])
 }
 
-fn do_split(list: List(a), n: Int, taken: List(a)) -> #(List(a), List(a)) {
-  case n <= 0 {
-    True -> #(reverse(taken), list)
-    False ->
-      case list {
-        [] -> #(reverse(taken), [])
-        [first, ..rest] -> do_split(rest, n - 1, [first, ..taken])
-      }
+fn repeat_loop(item: a, times: Int, acc: List(a)) -> List(a) {
+  case times <= 0 {
+    True -> acc
+    False -> repeat_loop(item, times - 1, [item, ..acc])
   }
 }
 
@@ -1528,20 +1517,16 @@ fn do_split(list: List(a), n: Int, taken: List(a)) -> #(List(a), List(a)) {
 /// ```
 ///
 pub fn split(list list: List(a), at index: Int) -> #(List(a), List(a)) {
-  do_split(list, index, [])
+  split_loop(list, index, [])
 }
 
-fn do_split_while(
-  list: List(a),
-  f: fn(a) -> Bool,
-  acc: List(a),
-) -> #(List(a), List(a)) {
-  case list {
-    [] -> #(reverse(acc), [])
-    [first, ..rest] ->
-      case f(first) {
-        False -> #(reverse(acc), list)
-        _ -> do_split_while(rest, f, [first, ..acc])
+fn split_loop(list: List(a), n: Int, taken: List(a)) -> #(List(a), List(a)) {
+  case n <= 0 {
+    True -> #(reverse(taken), list)
+    False ->
+      case list {
+        [] -> #(reverse(taken), [])
+        [first, ..rest] -> split_loop(rest, n - 1, [first, ..taken])
       }
   }
 }
@@ -1568,7 +1553,22 @@ pub fn split_while(
   list list: List(a),
   satisfying predicate: fn(a) -> Bool,
 ) -> #(List(a), List(a)) {
-  do_split_while(list, predicate, [])
+  split_while_loop(list, predicate, [])
+}
+
+fn split_while_loop(
+  list: List(a),
+  f: fn(a) -> Bool,
+  acc: List(a),
+) -> #(List(a), List(a)) {
+  case list {
+    [] -> #(reverse(acc), [])
+    [first, ..rest] ->
+      case f(first) {
+        False -> #(reverse(acc), list)
+        _ -> split_while_loop(rest, f, [first, ..acc])
+      }
+  }
 }
 
 /// Given a list of 2-element tuples, finds the first tuple that has a given
@@ -1640,17 +1640,6 @@ pub fn key_filter(
   })
 }
 
-fn do_pop(haystack, predicate, checked) {
-  case haystack {
-    [] -> Error(Nil)
-    [x, ..rest] ->
-      case predicate(x) {
-        True -> Ok(#(x, append(reverse(checked), rest)))
-        False -> do_pop(rest, predicate, [x, ..checked])
-      }
-  }
-}
-
 /// Removes the first element in a given list for which the predicate function returns `True`.
 ///
 /// Returns `Error(Nil)` if no such element is found.
@@ -1676,20 +1665,16 @@ pub fn pop(
   in list: List(a),
   one_that is_desired: fn(a) -> Bool,
 ) -> Result(#(a, List(a)), Nil) {
-  do_pop(list, is_desired, [])
+  pop_loop(list, is_desired, [])
 }
 
-fn do_pop_map(
-  list: List(a),
-  mapper: fn(a) -> Result(b, e),
-  checked: List(a),
-) -> Result(#(b, List(a)), Nil) {
-  case list {
+fn pop_loop(haystack, predicate, checked) {
+  case haystack {
     [] -> Error(Nil)
     [x, ..rest] ->
-      case mapper(x) {
-        Ok(y) -> Ok(#(y, append(reverse(checked), rest)))
-        Error(_) -> do_pop_map(rest, mapper, [x, ..checked])
+      case predicate(x) {
+        True -> Ok(#(x, append(reverse(checked), rest)))
+        False -> pop_loop(rest, predicate, [x, ..checked])
       }
   }
 }
@@ -1720,7 +1705,22 @@ pub fn pop_map(
   in haystack: List(a),
   one_that is_desired: fn(a) -> Result(b, c),
 ) -> Result(#(b, List(a)), Nil) {
-  do_pop_map(haystack, is_desired, [])
+  pop_map_loop(haystack, is_desired, [])
+}
+
+fn pop_map_loop(
+  list: List(a),
+  mapper: fn(a) -> Result(b, e),
+  checked: List(a),
+) -> Result(#(b, List(a)), Nil) {
+  case list {
+    [] -> Error(Nil)
+    [x, ..rest] ->
+      case mapper(x) {
+        Ok(y) -> Ok(#(y, append(reverse(checked), rest)))
+        Error(_) -> pop_map_loop(rest, mapper, [x, ..checked])
+      }
+  }
 }
 
 /// Given a list of 2-element tuples, finds the first tuple that has a given
@@ -1835,17 +1835,6 @@ pub fn try_each(
   }
 }
 
-fn do_partition(list, categorise, trues, falses) {
-  case list {
-    [] -> #(reverse(trues), reverse(falses))
-    [first, ..rest] ->
-      case categorise(first) {
-        True -> do_partition(rest, categorise, [first, ..trues], falses)
-        False -> do_partition(rest, categorise, trues, [first, ..falses])
-      }
-  }
-}
-
 /// Partitions a list into a tuple/pair of lists
 /// by a given categorisation function.
 ///
@@ -1862,7 +1851,18 @@ pub fn partition(
   list: List(a),
   with categorise: fn(a) -> Bool,
 ) -> #(List(a), List(a)) {
-  do_partition(list, categorise, [], [])
+  partition_loop(list, categorise, [], [])
+}
+
+fn partition_loop(list, categorise, trues, falses) {
+  case list {
+    [] -> #(reverse(trues), reverse(falses))
+    [first, ..rest] ->
+      case categorise(first) {
+        True -> partition_loop(rest, categorise, [first, ..trues], falses)
+        False -> partition_loop(rest, categorise, trues, [first, ..falses])
+      }
+  }
 }
 
 /// Returns all the permutations of a list.
@@ -1893,15 +1893,6 @@ pub fn permutations(list: List(a)) -> List(List(a)) {
   }
 }
 
-fn do_window(acc: List(List(a)), list: List(a), n: Int) -> List(List(a)) {
-  let window = take(list, n)
-
-  case length(window) == n {
-    True -> do_window([window, ..acc], drop(list, 1), n)
-    False -> acc
-  }
-}
-
 /// Returns a list of sliding windows.
 ///
 /// ## Examples
@@ -1919,7 +1910,16 @@ fn do_window(acc: List(List(a)), list: List(a), n: Int) -> List(List(a)) {
 pub fn window(list: List(a), by n: Int) -> List(List(a)) {
   case n <= 0 {
     True -> []
-    False -> do_window([], list, n) |> reverse
+    False -> window_loop([], list, n)
+  }
+}
+
+fn window_loop(acc: List(List(a)), list: List(a), n: Int) -> List(List(a)) {
+  let window = take(list, n)
+
+  case length(window) == n {
+    True -> window_loop([window, ..acc], drop(list, 1), n)
+    False -> reverse(acc)
   }
 }
 
@@ -1964,21 +1964,6 @@ pub fn drop_while(
   }
 }
 
-fn do_take_while(
-  list: List(a),
-  predicate: fn(a) -> Bool,
-  acc: List(a),
-) -> List(a) {
-  case list {
-    [] -> reverse(acc)
-    [first, ..rest] ->
-      case predicate(first) {
-        True -> do_take_while(rest, predicate, [first, ..acc])
-        False -> reverse(acc)
-      }
-  }
-}
-
 /// Takes the first elements in a given list for which the predicate function returns `True`.
 ///
 /// ## Examples
@@ -1992,28 +1977,21 @@ pub fn take_while(
   in list: List(a),
   satisfying predicate: fn(a) -> Bool,
 ) -> List(a) {
-  do_take_while(list, predicate, [])
+  take_while_loop(list, predicate, [])
 }
 
-fn do_chunk(
+fn take_while_loop(
   list: List(a),
-  f: fn(a) -> k,
-  previous_key: k,
-  current_chunk: List(a),
-  acc: List(List(a)),
-) -> List(List(a)) {
+  predicate: fn(a) -> Bool,
+  acc: List(a),
+) -> List(a) {
   case list {
-    [first, ..rest] -> {
-      let key = f(first)
-      case key == previous_key {
-        False -> {
-          let new_acc = [reverse(current_chunk), ..acc]
-          do_chunk(rest, f, key, [first], new_acc)
-        }
-        _true -> do_chunk(rest, f, key, [first, ..current_chunk], acc)
+    [] -> reverse(acc)
+    [first, ..rest] ->
+      case predicate(first) {
+        True -> take_while_loop(rest, predicate, [first, ..acc])
+        False -> reverse(acc)
       }
-    }
-    _empty -> reverse([reverse(current_chunk), ..acc])
   }
 }
 
@@ -2030,30 +2008,29 @@ fn do_chunk(
 pub fn chunk(in list: List(a), by f: fn(a) -> k) -> List(List(a)) {
   case list {
     [] -> []
-    [first, ..rest] -> do_chunk(rest, f, f(first), [first], [])
+    [first, ..rest] -> chunk_loop(rest, f, f(first), [first], [])
   }
 }
 
-fn do_sized_chunk(
+fn chunk_loop(
   list: List(a),
-  count: Int,
-  left: Int,
+  f: fn(a) -> k,
+  previous_key: k,
   current_chunk: List(a),
   acc: List(List(a)),
 ) -> List(List(a)) {
   case list {
-    [] ->
-      case current_chunk {
-        [] -> reverse(acc)
-        remaining -> reverse([reverse(remaining), ..acc])
-      }
     [first, ..rest] -> {
-      let chunk = [first, ..current_chunk]
-      case left > 1 {
-        False -> do_sized_chunk(rest, count, count, [], [reverse(chunk), ..acc])
-        True -> do_sized_chunk(rest, count, left - 1, chunk, acc)
+      let key = f(first)
+      case key == previous_key {
+        False -> {
+          let new_acc = [reverse(current_chunk), ..acc]
+          chunk_loop(rest, f, key, [first], new_acc)
+        }
+        _true -> chunk_loop(rest, f, key, [first, ..current_chunk], acc)
       }
     }
+    _empty -> reverse([reverse(current_chunk), ..acc])
   }
 }
 
@@ -2077,7 +2054,31 @@ fn do_sized_chunk(
 /// ```
 ///
 pub fn sized_chunk(in list: List(a), into count: Int) -> List(List(a)) {
-  do_sized_chunk(list, count, count, [], [])
+  sized_chunk_loop(list, count, count, [], [])
+}
+
+fn sized_chunk_loop(
+  list: List(a),
+  count: Int,
+  left: Int,
+  current_chunk: List(a),
+  acc: List(List(a)),
+) -> List(List(a)) {
+  case list {
+    [] ->
+      case current_chunk {
+        [] -> reverse(acc)
+        remaining -> reverse([reverse(remaining), ..acc])
+      }
+    [first, ..rest] -> {
+      let chunk = [first, ..current_chunk]
+      case left > 1 {
+        True -> sized_chunk_loop(rest, count, left - 1, chunk, acc)
+        False ->
+          sized_chunk_loop(rest, count, count, [], [reverse(chunk), ..acc])
+      }
+    }
+  }
 }
 
 /// This function acts similar to fold, but does not take an initial state.
@@ -2107,21 +2108,6 @@ pub fn reduce(over list: List(a), with fun: fn(a, a) -> a) -> Result(a, Nil) {
   }
 }
 
-fn do_scan(
-  list: List(a),
-  accumulator: acc,
-  accumulated: List(acc),
-  fun: fn(acc, a) -> acc,
-) -> List(acc) {
-  case list {
-    [] -> reverse(accumulated)
-    [first, ..rest] -> {
-      let next = fun(accumulator, first)
-      do_scan(rest, next, [next, ..accumulated], fun)
-    }
-  }
-}
-
 /// Similar to `fold`, but yields the state of the accumulator at each stage.
 ///
 /// ## Examples
@@ -2136,7 +2122,22 @@ pub fn scan(
   from initial: acc,
   with fun: fn(acc, a) -> acc,
 ) -> List(acc) {
-  do_scan(list, initial, [], fun)
+  scan_loop(list, initial, [], fun)
+}
+
+fn scan_loop(
+  list: List(a),
+  accumulator: acc,
+  accumulated: List(acc),
+  fun: fn(acc, a) -> acc,
+) -> List(acc) {
+  case list {
+    [] -> reverse(accumulated)
+    [first, ..rest] -> {
+      let next = fun(accumulator, first)
+      scan_loop(rest, next, [next, ..accumulated], fun)
+    }
+  }
 }
 
 /// Returns the last element in the given list.
@@ -2196,16 +2197,6 @@ pub fn combinations(items: List(a), by n: Int) -> List(List(a)) {
   }
 }
 
-fn do_combination_pairs(items: List(a)) -> List(List(#(a, a))) {
-  case items {
-    [] -> []
-    [first, ..rest] -> {
-      let first_combinations = map(rest, with: fn(other) { #(first, other) })
-      [first_combinations, ..do_combination_pairs(rest)]
-    }
-  }
-}
-
 /// Return unique pair combinations of elements in the list
 ///
 /// ## Examples
@@ -2216,10 +2207,20 @@ fn do_combination_pairs(items: List(a)) -> List(List(#(a, a))) {
 /// ```
 ///
 pub fn combination_pairs(items: List(a)) -> List(#(a, a)) {
-  do_combination_pairs(items)
+  combination_pairs_loop(items)
   |> flatten
 }
 
+fn combination_pairs_loop(items: List(a)) -> List(List(#(a, a))) {
+  case items {
+    [] -> []
+    [first, ..rest] -> {
+      let first_combinations = map(rest, with: fn(other) { #(first, other) })
+      [first_combinations, ..combination_pairs_loop(rest)]
+    }
+  }
+}
+
 /// Make a list alternating the elements from the given lists
 ///
 /// ## Examples
@@ -2270,22 +2271,6 @@ pub fn transpose(list_of_list: List(List(a))) -> List(List(a)) {
   }
 }
 
-fn do_shuffle_pair_unwrap(list: List(#(Float, a)), acc: List(a)) -> List(a) {
-  case list {
-    [] -> acc
-    [elem_pair, ..enumerable] ->
-      do_shuffle_pair_unwrap(enumerable, [elem_pair.1, ..acc])
-  }
-}
-
-fn do_shuffle_by_pair_indexes(
-  list_of_pairs: List(#(Float, a)),
-) -> List(#(Float, a)) {
-  sort(list_of_pairs, fn(a_pair: #(Float, a), b_pair: #(Float, a)) -> Order {
-    float.compare(a_pair.0, b_pair.0)
-  })
-}
-
 /// Takes a list, randomly sorts all items and returns the shuffled list.
 ///
 /// This function uses `float.random` to decide the order of the elements.
@@ -2301,5 +2286,21 @@ pub fn shuffle(list: List(a)) -> List(a) {
   list
   |> fold(from: [], with: fn(acc, a) { [#(float.random(), a), ..acc] })
   |> do_shuffle_by_pair_indexes()
-  |> do_shuffle_pair_unwrap([])
+  |> shuffle_pair_unwrap_loop([])
+}
+
+fn shuffle_pair_unwrap_loop(list: List(#(Float, a)), acc: List(a)) -> List(a) {
+  case list {
+    [] -> acc
+    [elem_pair, ..enumerable] ->
+      shuffle_pair_unwrap_loop(enumerable, [elem_pair.1, ..acc])
+  }
+}
+
+fn do_shuffle_by_pair_indexes(
+  list_of_pairs: List(#(Float, a)),
+) -> List(#(Float, a)) {
+  sort(list_of_pairs, fn(a_pair: #(Float, a), b_pair: #(Float, a)) -> Order {
+    float.compare(a_pair.0, b_pair.0)
+  })
 }
diff --git a/src/gleam/option.gleam b/src/gleam/option.gleam
index 7ada122..585ec2d 100644
--- a/src/gleam/option.gleam
+++ b/src/gleam/option.gleam
@@ -21,21 +21,6 @@ pub type Option(a) {
   None
 }
 
-fn do_all(list: List(Option(a)), acc: List(a)) -> Option(List(a)) {
-  case list {
-    [] -> Some(acc)
-    [x, ..rest] -> {
-      let accumulate = fn(acc, item) {
-        case acc, item {
-          Some(values), Some(value) -> Some([value, ..values])
-          _, _ -> None
-        }
-      }
-      accumulate(do_all(rest, acc), x)
-    }
-  }
-}
-
 /// Combines a list of `Option`s into a single `Option`.
 /// If all elements in the list are `Some` then returns a `Some` holding the list of values.
 /// If any element is `None` then returns`None`.
@@ -53,7 +38,22 @@ fn do_all(list: List(Option(a)), acc: List(a)) -> Option(List(a)) {
 /// ```
 ///
 pub fn all(list: List(Option(a))) -> Option(List(a)) {
-  do_all(list, [])
+  all_loop(list, [])
+}
+
+fn all_loop(list: List(Option(a)), acc: List(a)) -> Option(List(a)) {
+  case list {
+    [] -> Some(acc)
+    [x, ..rest] -> {
+      let accumulate = fn(acc, item) {
+        case acc, item {
+          Some(values), Some(value) -> Some([value, ..values])
+          _, _ -> None
+        }
+      }
+      accumulate(all_loop(rest, acc), x)
+    }
+  }
 }
 
 /// Checks whether the `Option` is a `Some` value.
@@ -328,21 +328,6 @@ pub fn lazy_or(first: Option(a), second: fn() -> Option(a)) -> Option(a) {
   }
 }
 
-fn do_values(list: List(Option(a)), acc: List(a)) -> List(a) {
-  case list {
-    [] -> acc
-    [first, ..rest] -> {
-      let accumulate = fn(acc, item) {
-        case item {
-          Some(value) -> [value, ..acc]
-          None -> acc
-        }
-      }
-      accumulate(do_values(rest, acc), first)
-    }
-  }
-}
-
 /// Given a list of `Option`s,
 /// returns only the values inside `Some`.
 ///
@@ -354,5 +339,20 @@ fn do_values(list: List(Option(a)), acc: List(a)) -> List(a) {
 /// ```
 ///
 pub fn values(options: List(Option(a))) -> List(a) {
-  do_values(options, [])
+  values_loop(options, [])
+}
+
+fn values_loop(list: List(Option(a)), acc: List(a)) -> List(a) {
+  case list {
+    [] -> acc
+    [first, ..rest] -> {
+      let accumulate = fn(acc, item) {
+        case item {
+          Some(value) -> [value, ..acc]
+          None -> acc
+        }
+      }
+      accumulate(values_loop(rest, acc), first)
+    }
+  }
 }
diff --git a/src/gleam/result.gleam b/src/gleam/result.gleam
index 235c347..65cae58 100644
--- a/src/gleam/result.gleam
+++ b/src/gleam/result.gleam
@@ -380,14 +380,14 @@ pub fn all(results: List(Result(a, e))) -> Result(List(a), e) {
 /// ```
 ///
 pub fn partition(results: List(Result(a, e))) -> #(List(a), List(e)) {
-  do_partition(results, [], [])
+  partition_loop(results, [], [])
 }
 
-fn do_partition(results: List(Result(a, e)), oks: List(a), errors: List(e)) {
+fn partition_loop(results: List(Result(a, e)), oks: List(a), errors: List(e)) {
   case results {
     [] -> #(oks, errors)
-    [Ok(a), ..rest] -> do_partition(rest, [a, ..oks], errors)
-    [Error(e), ..rest] -> do_partition(rest, oks, [e, ..errors])
+    [Ok(a), ..rest] -> partition_loop(rest, [a, ..oks], errors)
+    [Error(e), ..rest] -> partition_loop(rest, oks, [e, ..errors])
   }
 }
 
diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 14acc23..8a3a57e 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -435,13 +435,13 @@ pub fn concat(strings: List(String)) -> String {
 /// ```
 ///
 pub fn repeat(string: String, times times: Int) -> String {
-  do_repeat(string, times, "")
+  repeat_loop(string, times, "")
 }
 
-fn do_repeat(string: String, times: Int, acc: String) -> String {
+fn repeat_loop(string: String, times: Int, acc: String) -> String {
   case times <= 0 {
     True -> acc
-    False -> do_repeat(string, times - 1, acc <> string)
+    False -> repeat_loop(string, times - 1, acc <> string)
   }
 }
 
@@ -646,13 +646,13 @@ fn do_pop_grapheme(string string: String) -> Result(#(String, String), Nil)
 ///
 @external(javascript, "../gleam_stdlib.mjs", "graphemes")
 pub fn to_graphemes(string: String) -> List(String) {
-  do_to_graphemes(string, [])
+  to_graphemes_loop(string, [])
   |> list.reverse
 }
 
-fn do_to_graphemes(string: String, acc: List(String)) -> List(String) {
+fn to_graphemes_loop(string: String, acc: List(String)) -> List(String) {
   case pop_grapheme(string) {
-    Ok(#(grapheme, rest)) -> do_to_graphemes(rest, [grapheme, ..acc])
+    Ok(#(grapheme, rest)) -> to_graphemes_loop(rest, [grapheme, ..acc])
     _ -> acc
   }
 }
@@ -693,19 +693,18 @@ pub fn to_utf_codepoints(string: String) -> List(UtfCodepoint) {
 
 @target(erlang)
 fn do_to_utf_codepoints(string: String) -> List(UtfCodepoint) {
-  do_to_utf_codepoints_impl(<<string:utf8>>, [])
-  |> list.reverse
+  to_utf_codepoints_loop(<<string:utf8>>, [])
 }
 
 @target(erlang)
-fn do_to_utf_codepoints_impl(
+fn to_utf_codepoints_loop(
   bit_array: BitArray,
   acc: List(UtfCodepoint),
 ) -> List(UtfCodepoint) {
   case bit_array {
     <<first:utf8_codepoint, rest:bytes>> ->
-      do_to_utf_codepoints_impl(rest, [first, ..acc])
-    _ -> acc
+      to_utf_codepoints_loop(rest, [first, ..acc])
+    _ -> list.reverse(acc)
   }
 }