From ec5910bea4db98b40db374a2484380fe1892c563 Mon Sep 17 00:00:00 2001
From: Mistivia <i@mistivia.com>
Date: Tue, 24 Jun 2025 16:47:52 +0800
Subject: tailcalll on let block

---
 src/interp.c           | 8 ++++++++
 src/primitives.c       | 5 +++++
 tests/let-binding.lisp | 6 ++++++
 3 files changed, 19 insertions(+)

diff --git a/src/interp.c b/src/interp.c
index 80ddfed..65eeaff 100644
--- a/src/interp.c
+++ b/src/interp.c
@@ -478,6 +478,13 @@ SExpRef lisp_macroexpand1(Interp *interp, SExpRef macro, SExpRef args) {
     PUSH_REG(fn);
     SExpRef ret = lisp_apply(interp, fn, args, false);
     POP_REG();
+    while (VALTYPE(ret) == kTailcallSExp) {
+        fn = REF(ret)->tailcall.fn;
+        args = REF(ret)->tailcall.args;
+        PUSH_REG(ret);
+        ret = lisp_apply(interp, fn, args, false);
+        POP_REG();
+    }
     return ret;
 error:
     return new_error(interp, "macroexpand: syntax error.\n");
@@ -734,6 +741,7 @@ end:
     return ret;
 }
 
+
 SExpRef lisp_eval(Interp *interp, SExpRef sexp, bool istail) {
     if (interp->recursion_depth > 2048) {
         return new_error(interp, "eval: stack overflow.\n");
diff --git a/src/primitives.c b/src/primitives.c
index 5f70f09..8e56bf9 100644
--- a/src/primitives.c
+++ b/src/primitives.c
@@ -198,6 +198,11 @@ SExpRef primitive_let(Interp *interp, SExpRef args, bool istail) {
     }
 
     body = CDR(args);
+    if (istail) {
+        SExpRef closure = new_lambda(interp, NIL, body, env);
+        ret = new_tailcall(interp, closure, NIL);
+        goto end;
+    }
     iter = body;
     while (!NILP(iter)) {
         exp = CAR(iter);
diff --git a/tests/let-binding.lisp b/tests/let-binding.lisp
index eead06a..c132db8 100644
--- a/tests/let-binding.lisp
+++ b/tests/let-binding.lisp
@@ -22,3 +22,9 @@
   (assert (not (funcall my-evenp 9)))
   (assert (not (funcall my-oddp 10))))
 
+(assert
+  (= 2
+     (funcall
+       (lambda ()
+         (let () (return 2))
+         (return 1)))))
-- 
cgit v1.0