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src/list.c

@@ -0,0 +1,27 @@
+#include "list.h"
+
+intptr_t list_length(LispVal *list) {
+    assert(LISTP(list));
+    LispVal *tortise = list;
+    LispVal *hare = list;
+    intptr_t length = 0;
+    while (CONSP(tortise)) {
+        tortise = XCDR_SAFE(tortise);
+        hare = XCDR_SAFE(XCDR_SAFE(hare));
+        if (!NILP(hare) && tortise == hare) {
+            return -1;
+        }
+        ++length;
+    }
+    return length;
+}
+
+DEFUN(cons, "cons", (LispVal * car, LispVal *cdr), "(car cdr)",
+      "Construct a new cons object from CAR and CDR.") {
+    return CONS(car, cdr);
+}
+
+DEFUN(length, "length", (LispVal * list), "(list)", "") {
+    // TODO type check
+    return MAKE_FIXNUM(list_length(list));
+}