lisp: lisp_reset, vec: vec_reset

Reset method to "clear the memory" of a lisp object.  Only operates on
heap allocated objects.

include/alisp/lisp.h

@@ -49,6 +49,11 @@ typedef enum Tag
 #define INT_MIN  (-(INT_MAX + 1))
 
 tag_t tag_get(const lisp_t *);
+u64 tag_sizeof(tag_t);
+u64 lisp_sizeof(lisp_t *);
+lisp_t *lisp_reset(lisp_t *);
+void lisp_print(FILE *, lisp_t *);
+
 lisp_t *tag_smi(const i64);
 lisp_t *tag_sym(const char *);
 lisp_t *tag_cons(const cons_t *);
@@ -65,10 +70,6 @@ str_t *as_str(lisp_t *);
 #define CAR(L) (as_cons(L)->car)
 #define CDR(L) (as_cons(L)->cdr)
 
-void lisp_print(FILE *, lisp_t *);
-u64 tag_sizeof(tag_t);
-u64 lisp_sizeof(lisp_t *);
-
 #endif
 
 /* Copyright (C) 2026 Aryadev Chavali

include/alisp/vec.h

@@ -36,6 +36,7 @@ static_assert(sizeof(vec_t) == 64, "vec_t has to be 64 bytes as part of SBO");
 
 void vec_init(vec_t *, u64);
 void vec_free(vec_t *);
+void vec_reset(vec_t *);
 u8 *vec_data(vec_t *);
 
 // Append, possibly reallocating memory

src/lisp.c

@@ -238,6 +238,40 @@ u64 lisp_sizeof(lisp_t *lisp)
   return tag_sizeof(tag_get(lisp));
 }
 
+lisp_t *lisp_reset(lisp_t *lisp)
+{
+  switch (tag_get(lisp))
+  {
+  case TAG_NIL:
+  case TAG_SMI:
+  case TAG_SYM:
+    // Nothing to "reset" here.
+    return lisp;
+  case TAG_CONS:
+  {
+    // Make `car` and `cons` NIL
+    CAR(lisp) = NIL;
+    CDR(lisp) = NIL;
+    return lisp;
+  }
+  case TAG_VEC:
+  {
+    vec_reset(as_vec(lisp));
+    return lisp;
+  }
+  case TAG_STR:
+  {
+    vec_reset(&as_str(lisp)->data);
+    return lisp;
+  }
+  default:
+  {
+    FAIL("Unreachable");
+    return lisp;
+  }
+  }
+}
+
 /* Copyright (C) 2025, 2026 Aryadev Chavali
 
  * This program is distributed in the hope that it will be useful, but WITHOUT

src/vec.c

@@ -38,6 +38,14 @@ void vec_free(vec_t *vec)
   memset(vec, 0, sizeof(*vec));
 }
 
+void vec_reset(vec_t *vec)
+{
+  if (!vec)
+    return;
+  memset(vec_data(vec), 0, vec->capacity);
+  vec->size = 0;
+}
+
 u8 *vec_data(vec_t *vec)
 {
   return vec->not_inlined ? vec->ptr : vec->inlined;