[lang0] occurCheck -- a pass to create FnRecursive from Fn

- only in the same module for now

TODO.md

@@ -2,10 +2,7 @@
 
 > 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] `occurCheck` -- a pass to create `FnRecursive` from `Fn`
-
-- only in the same module for now
-
+[lang0] `assertEqual` & `assertNotEqual` improve error message
 [lang0] `equivalent` -- `FnRecursive`
 [lang0] `equivalentNeutral` -- `ApRecursive`
 

docs/lang0/examples/factorial.scm

@@ -0,0 +1,18 @@
+(import "./nat-church.scm" zero? add mul sub1)
+(import "./nat-church.scm" zero one two three four)
+(import "./boolean.scm" if true false)
+
+;; (claim factorial (-> Nat Nat))
+
+(define (factorial n)
+  (if (zero? n)
+    one
+    (mul n (factorial (sub1 n)))))
+
+factorial
+
+(assert-equal (factorial zero) one)
+(assert-equal (factorial one) one)
+(assert-equal (factorial two) two)
+(assert-equal (factorial three) (mul three two))
+(assert-equal (factorial four) (mul four (mul three two)))

docs/lang0/examples/nat-even-odd.scm

@@ -3,21 +3,13 @@
 (import "./nat-church.scm" one two three four)
 (import "./fix.scm" Y)
 
-(define even?
-  (let ([wrap (lambda (even?)
-                (lambda (n)
-                  (if (zero? n) true
-                      (if (zero? (sub1 n)) false
-                          (even? (sub1 (sub1 n)))))))])
-    (Y wrap)))
+(define (even? n)
+  (if (zero? n) true
+      (odd? (sub1 n))))
 
-(define odd?
-  (let ([wrap (lambda (odd?)
-                (lambda (n)
-                  (if (zero? n) false
-                      (if (zero? (sub1 n)) true
-                          (odd? (sub1 (sub1 n)))))))])
-    (Y wrap)))
+(define (odd? n)
+  (if (zero? n) false
+      (even? (sub1 n))))
 
 (assert-equal
   (even? zero)

package.json

@@ -28,7 +28,8 @@
     "@cicada-lang/framework": "^0.2.0",
     "@cicada-lang/sexp": "^0.1.2",
     "@xieyuheng/command-line": "^0.1.2",
-    "@xieyuheng/ty": "^0.2.1"
+    "@xieyuheng/ty": "^0.2.1",
+    "dedent": "^1.5.1"
   },
   "devDependencies": {
     "@types/node": "^20.12.4",

src/lang0/run/occurCheck.ts

@@ -1,6 +1,29 @@
+import dedent from "dedent"
 import type { Definition } from "../definition/Definition.js"
+import { expIndirectFreeNames } from "../exp/expIndirectFreeNames.js"
+import * as Exps from "../exp/index.js"
+import { formatExp } from "../format/formatExp.js"
 import type { Mod } from "../mod/index.js"
 
 export function occurCheck(mod: Mod, definition: Definition): void {
-  // TODO
+  const indirectFreeNames = expIndirectFreeNames(mod, definition.exp)
+
+  if (!indirectFreeNames.has(definition.name)) return
+
+  if (definition.exp["@kind"] !== "Fn") {
+    throw new Error(
+      dedent`
+        [occurCheck] Only function can be recursive
+
+          non-function exp: ${formatExp(definition.exp)}
+          recursive name: ${definition.name}
+        `,
+    )
+  }
+
+  definition.exp = Exps.FnRecursive(
+    definition.name,
+    definition.exp.name,
+    definition.exp.ret,
+  )
 }

src/lang0/run/runMod.ts

@@ -1,8 +1,8 @@
 import { modOwnDefinitions, type Mod } from "../mod/index.js"
 import { assertAllNamesDefined } from "./assertAllNamesDefined.js"
-import { occurCheck } from "./occurCheck.js"
 import { define } from "./define.js"
 import { execute } from "./execute.js"
+import { occurCheck } from "./occurCheck.js"
 
 export function runMod(mod: Mod): void {
   if (mod.isFinished) return