From 242c98edc4ab44e8de2e3888df91412965fe9bfe Mon Sep 17 00:00:00 2001
From: Simon Forman <sforman@hushmail.com>
Date: Mon, 20 Mar 2023 16:33:11 -0700
Subject: [PATCH] swap

---
 implementations/uvm-ncc/joy.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/implementations/uvm-ncc/joy.c b/implementations/uvm-ncc/joy.c
index a03d5ff..ca6a01b 100644
--- a/implementations/uvm-ncc/joy.c
+++ b/implementations/uvm-ncc/joy.c
@@ -560,6 +560,7 @@ text_to_expression(char *str)
 	return top;
 }
 
+
 /*
 In order to return two "pointers" I'm going to just OR them
 into one u64 value.  It might be conceptually cleaner to define
@@ -583,7 +584,8 @@ joy_eval(char *symbol, u32 stack, u32 expression)
 	else MATCH("pop") { stack = pop(stack); }
 	else MATCH("dup") { stack = dup(stack); }
 	else MATCH("stack") { stack = cons(stack, stack); }
-	// first, rest, swap, ...
+	else MATCH("swap") { stack = swap(stack); }
+	// first, rest, ...
 	//else MATCH("") { stack = (stack); }
 	CHECK_ERROR
 	//print_str(symbol);print_endl();
@@ -618,6 +620,23 @@ dup(u32 stack)
 }
 
 
+u32
+swap(u32 stack)
+{
+	u32 tos = pop_any(stack);
+	CHECK_ERROR
+	stack = tail(stack);
+	u32 second = pop_any(stack);
+	CHECK_ERROR
+	stack = tail(stack);
+	stack = cons(tos, stack);
+	CHECK_ERROR
+	stack = cons(second, stack);
+	CHECK_ERROR
+	return stack;
+}
+
+
 u32
 joy(u32 stack, u32 expression)
 {
@@ -670,7 +689,7 @@ main()
 	print_endl();
 	*/
 
-	u32 expression = text_to_expression("1 2 3 stack dup swaack");
+	u32 expression = text_to_expression("1 2 3 stack dup swaack swap");
 	//u32 expression = text_to_expression("1 2 3 clear 4 5 6");
 	//u32 expression = text_to_expression(" 1[2[true 3][aa[aa bb] aa bb cc]bob]false[]bob 3[4] ga[]ry");
 	print_joy_list(expression);