[lang0] Definition has optional indirectFreeNames

TODO.md

@@ -1,10 +1,13 @@
+`utils/setPop`
+
 # lang0
 
 > 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。
 
-[lang0] add a pass to handle `checkOccur`
+[lang0] `expIndirectFreeNames`
+
+[lang0] `checkOccur` -- a pass to create `FnRecursive` from `Fn`
 
-- check occur to create `FnRecursive` instead of `Fn`
 - only in the same module for now
 
 [lang0] `equivalent` -- `FnRecursive`

src/lang0/definition/Definition.ts

@@ -7,5 +7,6 @@ export type Definition = {
   name: string
   exp: Exp
   freeNames: Set<string>
+  indirectFreeNames?: Set<string>
   cache?: Value
 }

src/lang0/exp/expIndirectFreeNames.ts

@@ -0,0 +1,18 @@
+import type { Mod } from "../mod/Mod.js"
+import { modOwnDefinitions } from "../mod/modOwnDefinitions.js"
+import type { Exp } from "./Exp.js"
+import { expFreeNames } from "./expFreeNames.js"
+
+export function expIndirectFreeNames(mod: Mod, exp: Exp): Set<string> {
+  const freeNames = expFreeNames(new Set(), exp)
+  const ownDefinitions = modOwnDefinitions(mod)
+
+  const remainingNames = freeNames
+  const indirectFreeNames = new Set<string>()
+
+  while (remainingNames.size > 0) {
+    //
+  }
+
+  return indirectFreeNames
+}