[lang0] simplify freshen -- to only take set

TODO.md

@@ -1,6 +1,8 @@
+[lang0] move `utils/freshen` to top level
+[lang1] fix `freshen` -- be like lang0 with `usedNames`
+
 # lang1
 
-[lang1] fix `freshen` -- be like lang0 with `usedNames`
 [lang1] 支持 `(assert-equal)` 与 `(assert-not-equal)`
 [lang1] 支持直接递归函数与相互递归函数，不能判断等价的地方就不判断。
 

src/lang0/utils/freshen.test.ts

@@ -3,7 +3,7 @@ import { test } from "node:test"
 import { freshen } from "./freshen.js"
 
 test("freshen create new string not in set", () => {
-  assert.deepStrictEqual(freshen(["x"], "x"), "x₁")
-  assert.deepStrictEqual(freshen(["x", "x₁"], "x"), "x₂")
-  assert.deepStrictEqual(freshen(["x", "x₁", "x₂"], "x"), "x₃")
+  assert.deepStrictEqual(freshen(new Set(["x"]), "x"), "x₁")
+  assert.deepStrictEqual(freshen(new Set(["x", "x₁"]), "x"), "x₂")
+  assert.deepStrictEqual(freshen(new Set(["x", "x₁", "x₂"]), "x"), "x₃")
 })

src/lang0/utils/freshen.ts

@@ -1,9 +1,6 @@
 import { stringToSubscript } from "../../utils/stringToSubscript.js"
 
-export function freshen(
-  usedNames: Array<string> | Set<string>,
-  name: string,
-): string {
+export function freshen(usedNames: Set<string>, name: string): string {
   usedNames = new Set(usedNames)
   let counter = 1
   let freshName = name