1 files changed, 57 insertions, 0 deletions
diff --git a/src/libzisp/value/pair.zig b/src/libzisp/value/pair.zig
new file mode 100644
index 0000000..541a5f5
--- /dev/null
+++ b/src/libzisp/value/pair.zig
@@ -0,0 +1,57 @@
+const std = @import("std");
+const value = @import("../value.zig");
+const gc = @import("../gc.zig");
+
+const ptr = @import("ptr.zig");
+
+const Value = value.Value;
+
+// Zig API
+
+pub fn check(v: Value) bool {
+    return ptr.checkZisp(v, .pair);
+}
+
+pub fn assert(v: Value) void {
+    if (!check(v)) {
+        v.dump();
+        @panic("not pair");
+    }
+}
+
+// Zisp API
+
+pub fn pred(v: Value) Value {
+    return value.boole.pack(check(v));
+}
+
+pub fn cons(v1: Value, v2: Value) Value {
+    const mem = gc.alloc(2);
+    mem[0] = .{ .value = v1 };
+    mem[1] = .{ .value = v2 };
+    return ptr.pack(mem.ptr, .pair);
+}
+
+fn getMem(v: Value) *[2]Value {
+    return @ptrCast(ptr.unpack(v).@"0");
+}
+
+pub fn car(v: Value) Value {
+    assert(v);
+    return getMem(v)[0];
+}
+
+pub fn cdr(v: Value) Value {
+    assert(v);
+    return getMem(v)[1];
+}
+
+pub fn setcar(v: Value, new: Value) void {
+    assert(v);
+    getMem(v)[0] = new;
+}
+
+pub fn setcdr(v: Value, new: Value) void {
+    assert(v);
+    getMem(v)[1] = new;
+}