chore: add join

packages/abitype/src/human-readable/join.test.ts

@@ -0,0 +1,12 @@
+import { attest } from '@arktype/attest'
+import { expect, test } from 'vitest'
+
+import { join } from './join.js'
+
+test('default', () => {
+  const res = join(['foo', 'bar', 'baz'], ' ')
+  attest.instantiations([45, 'instantiations'])
+
+  expect(res).toMatchInlineSnapshot(`"foo bar baz"`)
+  attest(res).snap('foo bar baz')
+})

packages/abitype/src/human-readable/join.ts

@@ -0,0 +1,15 @@
+export type join<
+  list extends readonly unknown[],
+  separator extends string,
+> = list extends readonly [infer head, ...infer tail]
+  ? tail['length'] extends 0
+    ? `${head & string}`
+    : `${head & string}${separator}${join<tail, separator>}`
+  : never
+
+export function join<
+  const list extends readonly unknown[],
+  separator extends string,
+>(list: list, separator: separator): join<list, separator> {
+  return list.join(separator) as join<list, separator>
+}