update

1 files changed, 20 insertions, 0 deletions

diff --git a/src/libzisp/lib/list.zig b/src/libzisp/lib/list.zig
new file mode 100644
index 0000000..9d6a6bc
--- /dev/null
+++ b/src/libzisp/lib/list.zig
@@ -0,0 +1,20 @@
+const value = @import("../value.zig");
+
+const Value = value.Value;
+
+pub fn reverse(list: Value) Value {
+    return reverseWithTail(list, value.nil.nil);
+}
+
+pub fn reverseWithTail(list: Value, tail: Value) Value {
+    var head = list;
+    var result = tail;
+    while (!value.nil.check(head)) {
+        value.pair.assert(head);
+        const car = value.pair.car(head);
+        const cdr = value.pair.cdr(head);
+        result = value.pair.cons(car, result);
+        head = cdr;
+    }
+    return result;
+}