add string.inspect() (#296)

2 files changed, 77 insertions, 6 deletions

diff --git a/src/gleam/string.gleam b/src/gleam/string.gleam
index 45d4d31..d06e2dd 100644
--- a/src/gleam/string.gleam
+++ b/src/gleam/string.gleam
@@ -823,3 +823,18 @@ pub fn capitalise(s: String) -> String {
     _ -> ""
   }
 }
+
+pub fn inspect(value: a) -> String {
+  do_inspect(value)
+  |> string_builder.to_string
+}
+
+if javascript {
+  external fn do_inspect(value: a) -> string_builder.StringBuilder =
+    "../gleam.mjs" "inspect"
+}
+
+if erlang {
+  external fn do_inspect(value: a) -> string_builder.StringBuilder =
+    "gleam_stdlib" "inspect"
+}
diff --git a/src/gleam_stdlib.erl b/src/gleam_stdlib.erl
index cc1475f..9dc769b 100644
--- a/src/gleam_stdlib.erl
+++ b/src/gleam_stdlib.erl
@@ -9,7 +9,8 @@
          bit_string_slice/3, decode_bit_string/1, compile_regex/2, regex_scan/2,
          percent_encode/1, percent_decode/1, regex_check/2, regex_split/2,
          base_decode64/1, parse_query/1, bit_string_concat/1, size_of_tuple/1,
-         decode_tuple/1, tuple_get/2, classify_dynamic/1, print/1, println/1]).
+         decode_tuple/1, tuple_get/2, classify_dynamic/1, print/1, println/1,
+         inspect/1]).
 
 %% Taken from OTP's uri_string module
 -define(DEC2HEX(X),
@@ -47,9 +48,9 @@ classify_dynamic(X) when is_float(X) -> <<"Float">>;
 classify_dynamic(X) when is_list(X) -> <<"List">>;
 classify_dynamic(X) when is_boolean(X) -> <<"Bool">>;
 classify_dynamic(X) when is_map(X) -> <<"Map">>;
-classify_dynamic(X) when is_tuple(X) -> 
+classify_dynamic(X) when is_tuple(X) ->
     iolist_to_binary(["Tuple of ", integer_to_list(tuple_size(X)), " elements"]);
-classify_dynamic(X) when 
+classify_dynamic(X) when
     is_function(X, 0) orelse is_function(X, 1) orelse is_function(X, 2) orelse
     is_function(X, 3) orelse is_function(X, 4) orelse is_function(X, 5) orelse
     is_function(X, 6) orelse is_function(X, 7) orelse is_function(X, 8) orelse
@@ -81,7 +82,7 @@ decode_list(Data) -> decode_error_msg(<<"List">>, Data).
 decode_field(Data, Key) ->
     case Data of
         #{Key := Value} -> {ok, Value};
-        _ -> 
+        _ ->
             decode_error(<<"field"/utf8>>, <<"nothing"/utf8>>)
     end.
 
@@ -227,7 +228,7 @@ wrap_list(X) -> [X].
 parse_query(Query) ->
     case uri_string:dissect_query(Query) of
         {error, _, _} -> {error, nil};
-        Pairs -> 
+        Pairs ->
             Pairs1 = lists:map(fun
                 ({K, true}) -> {K, <<"">>};
                 (Pair) -> Pair
@@ -296,7 +297,7 @@ uri_parse(String) ->
                 maps_get_optional(Uri, userinfo),
                 maps_get_optional(Uri, host),
                 maps_get_optional(Uri, port),
-                maps_get_or(Uri, path, <<>>), 
+                maps_get_or(Uri, path, <<>>),
                 maps_get_optional(Uri, query),
                 maps_get_optional(Uri, fragment)
             }}
@@ -319,3 +320,58 @@ print(String) ->
 println(String) ->
     io:put_chars([String, $\n]),
     nil.
+
+inspect(true) ->
+    "True";
+inspect(false) ->
+    "False";
+inspect(Any) when is_atom(Any) ->
+    lists:map(
+        fun(Part) ->
+            [Head | Tail] = string:next_grapheme(unicode:characters_to_binary(Part)),
+            [string:uppercase([Head]), Tail]
+        end,
+        re:split(erlang:atom_to_list(Any), "_+", [{return, iodata}])
+    );
+inspect(Any) when is_integer(Any) ->
+    erlang:integer_to_list(Any);
+inspect(Any) when is_float(Any) ->
+    io_lib_format:fwrite_g(Any);
+inspect(Any) when is_binary(Any) ->
+    Pattern = [$"],
+    Replacement = [$\\, $\\, $"],
+    Escaped = re:replace(Any, Pattern, Replacement, [{return, binary}, global]),
+    ["\"", Escaped, "\""];
+inspect(Any) when is_list(Any) ->
+    ["[",
+        lists:join(<<", ">>,
+            lists:map(fun inspect/1, Any)
+        ),
+    "]"];
+inspect(Any) when is_tuple(Any) % Record constructors
+  andalso is_atom(element(1, Any))
+  andalso element(1, Any) =/= false
+  andalso element(1, Any) =/= true
+  andalso element(1, Any) =/= nil
+->
+    [Atom | ArgsList] = erlang:tuple_to_list(Any),
+    Args =
+        lists:join(<<", ">>,
+            lists:map(fun inspect/1, ArgsList)
+    ),
+    [inspect(Atom), "(", Args, ")"];
+inspect(Any) when is_tuple(Any) ->
+    ["#(",
+        lists:join(<<", ">>,
+            lists:map(fun inspect/1, erlang:tuple_to_list(Any))
+        ),
+    ")"];
+inspect(Any) when is_function(Any) ->
+    {arity, Arity} = erlang:fun_info(Any, arity),
+    ArgsAsciiCodes = lists:seq($a, $a + Arity - 1),
+    Args = lists:join(<<", ">>,
+        lists:map(fun(Arg) -> <<Arg>> end, ArgsAsciiCodes)
+    ),
+    ["//fn(", Args, ") { ... }"];
+inspect(Any) ->
+    ["//erl(", io_lib:format("~p", [Any]), ")"].