1 files changed, 62 insertions, 0 deletions
diff --git a/src/gleam_stdlib.mjs b/src/gleam_stdlib.mjs
index b2c82c4..8edbe2f 100644
--- a/src/gleam_stdlib.mjs
+++ b/src/gleam_stdlib.mjs
@@ -8,6 +8,8 @@ import {
   stringBits,
   toBitString,
   NonEmpty,
+  CustomType,
+  BitArray,
 } from "./gleam.mjs";
 import {
   CompileError as RegexCompileError,
@@ -781,3 +783,63 @@ export function bitwise_shift_left(x, y) {
 export function bitwise_shift_right(x, y) {
   return Number(BigInt(x) >> BigInt(y));
 }
+
+export function inspect(v) {
+  const t = typeof v;
+  if (v === true) return "True";
+  if (v === false) return "False";
+  if (v === null) return "//js(null)";
+  if (v === undefined) return "Nil";
+  if (t === "string") return JSON.stringify(v);
+  if (t === "bigint" || t === "number") return v.toString();
+  if (Array.isArray(v)) return `#(${v.map(inspect).join(", ")})`;
+  if (v instanceof List) return inspectList(v);
+  if (v instanceof UtfCodepoint) return inspectUtfCodepoint(v);
+  if (v instanceof BitArray) return inspectBitArray(v);
+  if (v instanceof CustomType) return inspectCustomType(v);
+  if (v instanceof Set) return `//js(Set(${[...v].map(inspect).join(", ")}))`;
+  if (v instanceof RegExp) return `//js(${v})`;
+  if (v instanceof Date) return `//js(Date("${v.toISOString()}"))`;
+  if (v instanceof Function) {
+    const args = [];
+    for (const i of Array(v.length).keys())
+      args.push(String.fromCharCode(i + 97));
+    return `//fn(${args.join(", ")}) { ... }`;
+  }
+  return inspectObject(v);
+}
+
+function inspectObject(v) {
+  const name = Object.getPrototypeOf(v)?.constructor?.name || "Object";
+  const props = [];
+  for (const k of Object.keys(v)) {
+    props.push(`${inspect(k)}: ${inspect(v[k])}`);
+  }
+  const body = props.length ? " " + props.join(", ") + " " : "";
+  const head = name === "Object" ? "" : name + " ";
+  return `//js(${head}{${body}})`;
+}
+
+function inspectCustomType(record) {
+  const props = Object.keys(record)
+    .map((label) => {
+      const value = inspect(record[label]);
+      return isNaN(parseInt(label)) ? `${label}: ${value}` : value;
+    })
+    .join(", ");
+  return props
+    ? `${record.constructor.name}(${props})`
+    : record.constructor.name;
+}
+
+export function inspectList(list) {
+  return `[${list.toArray().map(inspect).join(", ")}]`;
+}
+
+export function inspectBitArray(bits) {
+  return `<<${Array.from(bits.buffer).join(", ")}>>`;
+}
+
+export function inspectUtfCodepoint(codepoint) {
+  return `//utfcodepoint(${String.fromCodePoint(codepoint.value)})`;
+}