Echo improvements

lpil · lpil · commit d6ef6c510a8a · 2025-06-15T10:59:38.000+01:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -12,6 +12,10 @@
   definitions are not longer generated.
   ([Louis Pilfold](https://github.com/lpil))
 
+- `echo` now has better support for character lists, JavaScript errors, and
+  JavaScript circular references.
+  ([Louis Pilfold](https://github.com/lpil))
+
 ### Build tool
 
 - `gleam update`, `gleam deps update`, and `gleam deps download` will now print
@@ -28,7 +32,7 @@
   lustre     3.1.4 -> 5.1.1
   ```
 
-  ([Amjad Mohamed ](https://github.com/andho))
+  ([Amjad Mohamed](https://github.com/andho))
 
 
 ### Language server
diff --git a/compiler-core/src/javascript.rs b/compiler-core/src/javascript.rs
@@ -140,11 +140,11 @@ impl<'a> Generator<'a> {
             self.register_prelude_usage(&mut imports, "toList", None);
         };
 
-        if self.tracker.list_empty_class_used {
+        if self.tracker.list_empty_class_used || self.tracker.echo_used {
             self.register_prelude_usage(&mut imports, "Empty", Some("$Empty"));
         };
 
-        if self.tracker.list_non_empty_class_used {
+        if self.tracker.list_non_empty_class_used || self.tracker.echo_used {
             self.register_prelude_usage(&mut imports, "NonEmpty", Some("$NonEmpty"));
         };
 
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_in_a_pipeline.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_in_a_pipeline.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 79
 expression: "\npub fn main() {\n  [1, 2, 3]\n  |> echo\n  |> wibble\n}\n\npub fn wibble(n) { n }\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -17,6 +19,8 @@ pub fn wibble(n) { n }
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
   toList,
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_block.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_block.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 65
 expression: "\npub fn main() {\n  echo {\n    Nil\n    1\n  }\n}\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -15,6 +17,8 @@ pub fn main() {
 ----- COMPILED JAVASCRIPT
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_case_expression.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_case_expression.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 28
 expression: "\npub fn main() {\n  echo case 1 {\n    _ -> 2\n  }\n}\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -14,6 +16,8 @@ pub fn main() {
 ----- COMPILED JAVASCRIPT
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_function_call.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_function_call.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 52
 expression: "\npub fn main() {\n  echo wibble(1, 2)\n}\n\nfn wibble(n: Int, m: Int) { n + m }\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -14,6 +16,8 @@ fn wibble(n: Int, m: Int) { n + m }
 ----- COMPILED JAVASCRIPT
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_panic.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_panic.snap
@@ -14,6 +14,8 @@ pub fn main() {
 ----- COMPILED JAVASCRIPT
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   makeError,
   bitArraySlice,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_simple_expression.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__echo_with_a_simple_expression.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 5
 expression: "\npub fn main() {\n  echo 1\n}\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -12,6 +14,8 @@ pub fn main() {
 ----- COMPILED JAVASCRIPT
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__module_named_inspect.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__module_named_inspect.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 112
 expression: "\nimport other/inspect\n\npub fn main() {\n  echo inspect.x\n}\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -15,6 +17,8 @@ pub fn main() {
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import * as $inspect from "../../other/other/inspect.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__multiple_echos_in_a_pipeline.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__multiple_echos_in_a_pipeline.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 94
 expression: "\npub fn main() {\n  [1, 2, 3]\n  |> echo\n  |> wibble\n  |> echo\n  |> wibble\n  |> echo\n}\n\npub fn wibble(n) { n }\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -20,6 +22,8 @@ pub fn wibble(n) { n }
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
   toList,
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__multiple_echos_inside_expression.snap b/compiler-core/src/javascript/tests/snapshots/gleam_core__javascript__tests__echo__multiple_echos_inside_expression.snap
@@ -1,6 +1,8 @@
 ---
 source: compiler-core/src/javascript/tests/echo.rs
+assertion_line: 16
 expression: "\npub fn main() {\n  echo 1\n  echo 2\n}\n"
+snapshot_kind: text
 ---
 ----- SOURCE CODE
 
@@ -13,6 +15,8 @@ pub fn main() {
 ----- COMPILED JAVASCRIPT
 import * as $stdlib$dict from "../../gleam_stdlib/dict.mjs";
 import {
+  Empty as $Empty,
+  NonEmpty as $NonEmpty,
   CustomType as $CustomType,
   bitArraySlice,
   bitArraySliceToInt,
diff --git a/compiler-core/templates/echo.erl b/compiler-core/templates/echo.erl
@@ -1,6 +1,15 @@
--define(is_lowercase_char(X), (X > 96 andalso X < 123)).
--define(is_underscore_char(X), (X == 95)).
--define(is_digit_char(X), (X > 47 andalso X < 58)).
+-define(is_lowercase_char(X),
+    (X > 96 andalso X < 123)).
+
+-define(is_underscore_char(X),
+    (X == 95)).
+
+-define(is_digit_char(X),
+    (X > 47 andalso X < 58)).
+
+-define(is_ascii_character(X),
+    (erlang:is_integer(X) andalso X >= 32 andalso X =< 126)).
+
 -define(could_be_record(Tuple),
     erlang:is_tuple(Tuple) andalso
         erlang:is_atom(erlang:element(1, Tuple)) andalso
@@ -80,7 +89,8 @@ inspect@atom(Atom) ->
     end.
 
 inspect@list(List) ->
-    case inspect@proper_or_improper_list(List) of
+    case inspect@list_loop(List, true) of
+        {charlist, _} -> ["charlist.from_string(\"", erlang:list_to_binary(List), "\")"];
         {proper, Elements} -> ["[", Elements, "]"];
         {improper, Elements} -> ["//erl([", Elements, "])"]
     end.
@@ -141,14 +151,17 @@ inspect@escape_grapheme(Char) ->
 inspect@convert_to_u(Code) ->
     erlang:list_to_binary(io_lib:format("\\u{~4.16.0B}", [Code])).
 
-inspect@proper_or_improper_list(List) ->
+inspect@list_loop(List, Ascii) ->
     case List of
         [] ->
             {proper, []};
+        [First] when Ascii andalso ?is_ascii_character(First) ->
+            {charlist, nil};
         [First] ->
             {proper, [echo@inspect(First)]};
         [First | Rest] when erlang:is_list(Rest) ->
-            {Kind, Inspected} = inspect@proper_or_improper_list(Rest),
+            StillAscii = Ascii andalso ?is_ascii_character(First),
+            {Kind, Inspected} = inspect@list_loop(Rest, StillAscii),
             {Kind, [echo@inspect(First), ", " | Inspected]};
         [First | ImproperRest] ->
             {improper, [echo@inspect(First), " | ", echo@inspect(ImproperRest)]}
diff --git a/compiler-core/templates/echo.mjs b/compiler-core/templates/echo.mjs
@@ -93,26 +93,66 @@ function echo$inspect(v) {
   if (v === undefined) return "Nil";
   if (t === "string") return echo$inspectString(v);
   if (t === "bigint" || t === "number") return v.toString();
-  if (globalThis.Array.isArray(v))
-    return `#(${v.map(echo$inspect).join(", ")})`;
-  if (v instanceof $List)
-    return `[${v.toArray().map(echo$inspect).join(", ")}]`;
   if (v instanceof $UtfCodepoint)
     return `//utfcodepoint(${String.fromCodePoint(v.value)})`;
   if (v instanceof $BitArray) return echo$inspectBitArray(v);
-  if (v instanceof $CustomType) return echo$inspectCustomType(v);
-  if (echo$isDict(v)) return echo$inspectDict(v);
-  if (v instanceof Set)
-    return `//js(Set(${[...v].map(echo$inspect).join(", ")}))`;
   if (v instanceof RegExp) return `//js(${v})`;
   if (v instanceof Date) return `//js(Date("${v.toISOString()}"))`;
+  if (v instanceof globalThis.Error) return `//js(${v.toString()})`;
   if (v instanceof Function) {
     const args = [];
     for (const i of Array(v.length).keys())
       args.push(String.fromCharCode(i + 97));
     return `//fn(${args.join(", ")}) { ... }`;
   }
-  return echo$inspectObject(v);
+
+  try {
+    if (globalThis.Array.isArray(v))
+      return `#(${v.map(echo$inspect).join(", ")})`;
+    if (v instanceof $List) return echo$inspectList(v);
+    if (v instanceof $CustomType) return echo$inspectCustomType(v);
+    if (echo$isDict(v)) return echo$inspectDict(v);
+    if (v instanceof Set)
+      return `//js(Set(${[...v].map(echo$inspect).join(", ")}))`;
+    return echo$inspectObject(v);
+  } catch (e) {
+    if (e instanceof RangeError) return "//js(circular)";
+    throw e;
+  }
+}
+
+export function echo$inspectList(list) {
+  if (list instanceof $Empty) {
+    return "[]";
+  }
+
+  let char_out = 'charlist.from_string("';
+  let list_out = "[";
+
+  let current = list;
+  while (current instanceof $NonEmpty) {
+    let element = current.head;
+    current = current.tail;
+
+    if (list_out !== "[") {
+      list_out += ", ";
+    }
+    list_out += echo$inspect(element);
+
+    if (char_out) {
+      if (Number.isInteger(element) && element >= 32 && element <= 126) {
+        char_out += String.fromCharCode(element);
+      } else {
+        char_out = null;
+      }
+    }
+  }
+
+  if (char_out) {
+    return char_out + '")';
+  } else {
+    return list_out + "]";
+  }
 }
 
 function echo$inspectBitArray(bitArray) {
diff --git a/test-output/cases/echo_charlist/gleam.toml b/test-output/cases/echo_charlist/gleam.toml
@@ -0,0 +1,2 @@
+name = "echo_charlist"
+version = "1.0.0"
diff --git a/test-output/cases/echo_charlist/src/main.gleam b/test-output/cases/echo_charlist/src/main.gleam
@@ -0,0 +1,3 @@
+pub fn main() {
+  echo [72, 101, 108, 108, 111, 44, 32, 74, 111, 101, 33]
+}
diff --git a/test-output/src/tests/echo.rs b/test-output/src/tests/echo.rs
@@ -134,6 +134,11 @@ fn echo_bool() {
     assert_echo!("echo_bool");
 }
 
+#[test]
+fn echo_charlist() {
+    assert_echo!("echo_charlist");
+}
+
 #[test]
 fn echo_custom_type() {
     assert_echo!(Target::Erlang, "echo_custom_type");
diff --git a/test-output/src/tests/snapshots/test_output__tests__echo__echo_charlist.snap b/test-output/src/tests/snapshots/test_output__tests__echo__echo_charlist.snap
@@ -0,0 +1,15 @@
+---
+source: test-output/src/tests/echo.rs
+assertion_line: 139
+expression: output
+snapshot_kind: text
+---
+--- main.gleam ----------------------
+pub fn main() {
+  echo [72, 101, 108, 108, 111, 44, 32, 74, 111, 101, 33]
+}
+
+
+--- gleam run output ----------------
+[90msrc/main.gleam:2[39m
+charlist.from_string("Hello, Joe!")
