From fd2ba3b67dcdc10cbdafe4066c021f2888cdfb2a Mon Sep 17 00:00:00 2001
From: Simon Forman <sforman@hushmail.com>
Date: Fri, 3 Mar 2023 07:31:52 -0800
Subject: [PATCH] Joy in UVM NCC code.

---
 implementations/uvm-ncc/joy_types.c | 109 ++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 implementations/uvm-ncc/joy_types.c

diff --git a/implementations/uvm-ncc/joy_types.c b/implementations/uvm-ncc/joy_types.c
new file mode 100644
index 0000000..876cc38
--- /dev/null
+++ b/implementations/uvm-ncc/joy_types.c
@@ -0,0 +1,109 @@
+#include <uvm/syscalls.h>
+// In the Thun dialect of Joy we have four types of values:
+// Integers, Booleans, Symbols, and Lists.
+// We don't have Unions, Enums, or Typedefs.
+//
+// So how do we represent Joy types?
+//
+// In SICP they use a pair of arrays of pointers, one for heads and one
+// for tails.
+
+#define HEAP_SIZE 1024
+
+u32 heads[HEAP_SIZE];
+u32 tails[HEAP_SIZE];
+
+// > A pointer to a pair is an index into the two vectors.
+
+u32 free = 0;
+
+// > We also need a representation for objects other than pairs (such as
+// numbers and symbols) and a way to distinguish one kind of data from
+// another. There are many methods of accomplishing this, but they all
+// reduce to using typed pointers, that is, to extending the notion of
+// ``pointer'' to include information on data type. 
+
+#define TYPE_OF(pointer) (pointer >> 30)
+#define VALUE_OF(pointer) (pointer & 0x3fffffff)
+#define JOY_VALUE(type, value) ((type & 3) << 30) | (value & 0x3fffffff)
+
+u8 joyInt = 0;
+u8 joyList = 1;
+u8 joySymbol = 2;
+u8 joyBool = 3;
+
+u32 empty_list = 0x3fffffff;
+
+u32
+cons(u32 head, u32 tail)
+{
+	if (free >= HEAP_SIZE)
+		return -1;
+
+	heads[free] = head;
+	tails[free] = tail;
+	u32 cell = JOY_VALUE(joyList, free);
+	++free;
+	return cell;
+}
+
+u32 head(u32 list) { return heads[VALUE_OF(list)]; }
+u32 tail(u32 list) { return tails[VALUE_OF(list)]; }
+
+
+void
+print_joy_value(u32 jv)
+{
+	u8 type = TYPE_OF(jv);
+	if (type == joyInt) {
+		print_i64(VALUE_OF(jv));
+	} else if (type == joyBool) {
+		print_str(VALUE_OF(jv) ? "true" : "false");
+	} else if (type == joyList) {
+		print_str("[");
+		print_joy_list(jv);
+		print_str("]");
+	} else if (type == joySymbol) {
+		// print_str(symbols[VALUE_OF(jv)]);
+	}
+}
+
+void
+print_joy_list(u32 list)
+{
+	if (TYPE_OF(list) != joyList) {
+		1/0;
+	}
+	while (list != empty_list) {
+		print_joy_value(head(list));
+		list = tail(list);
+		if (list != empty_list) {
+			print_str(" ");
+		}
+	}
+}
+
+void
+main()
+{
+	u32 joy_true = JOY_VALUE(joyBool, 1);
+	u32 joy_false = JOY_VALUE(joyBool, 0);
+
+	u32 el = empty_list;
+	el = cons(48, el);
+	el = cons(el, el);
+
+	u32 stack = empty_list;
+
+	stack = cons(23, stack);
+	stack = cons(joy_true, stack);
+	stack = cons(42, stack);
+	stack = cons(el, stack);
+	stack = cons(joy_false, stack);
+	stack = cons(273, stack);
+	print_joy_list(stack);
+	print_endl();
+}
+
+
+