From f440716bf9564f0cbb0c72f73a23df5e447171db Mon Sep 17 00:00:00 2001
From: Peter McGoron <code@mcgoron.com>
Date: Tue, 16 Jul 2024 14:46:27 -0400
Subject: [PATCH] uns_lisp: swap

---
 examples/lisp/uns_lisp.c | 47 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/examples/lisp/uns_lisp.c b/examples/lisp/uns_lisp.c
index f6760a9..d58b0c9 100644
--- a/examples/lisp/uns_lisp.c
+++ b/examples/lisp/uns_lisp.c
@@ -1035,6 +1035,7 @@ enum cps_return {
 	CPS_EXEC_INVALID_APPL_LIST,
 	CPS_APP_UNDERFLOW,
 	CPS_FCALL_IMPROPER_LIST,
+	CPS_SWAP_UNDERFLOW,
 
 	CPS_RETURN_LEN
 };
@@ -1071,6 +1072,7 @@ static const char *cps_return_to_string[CPS_RETURN_LEN] = {
 	"CPS_EXEC_INVALID_APPL_LIST",
 	"CPS_APP_UNDERFLOW",
 	"CPS_FCALL_IMPROPER_LIST",
+	"CPS_SWAP_UNDERFLOW"
 };
 
 /* {K (quote QUOTED)} {cps} = {(-> (quote QUOTED) K)} */
@@ -1738,6 +1740,49 @@ end:
 	return r;
 }
 
+static enum cps_return cps_swap(struct uns_ctr *prevstack,
+                                int places,
+                                struct uns_ctr *readstack
+                               )
+{
+	struct uns_ctr top = {0};
+	struct uns_ctr tmp = {0};
+	struct uns_ctr tmpstack = {0};
+	enum cps_return r = CPS_CONTINUE;
+	int i;
+
+	uns_root_add(gc, &top);
+	uns_root_add(gc, &tmp);
+	uns_root_add(gc, &tmpstack);
+
+	if (!stack_pop(prevstack, &top)) {
+		r = CPS_SWAP_UNDERFLOW;
+		goto end;
+	}
+
+	tmpstack.p = empty_list.p;
+	for (i = 0; i < places; i++) {
+		if (!stack_pop(prevstack, &tmp)) {
+			r = CPS_SWAP_UNDERFLOW;
+			goto end;
+		}
+		stack_push(&tmpstack, &tmp);
+	}
+
+	tmp.p = tmpstack.p;
+	stack_push(prevstack, &top);
+	for (i = 0; i < places; i++) {
+		stack_pop(&tmpstack, &tmp);
+		stack_push(prevstack, &tmp);
+	}
+
+end:
+	uns_root_remove(gc, &top);
+	uns_root_remove(gc, &tmp);
+	uns_root_remove(gc, &tmpstack);
+	return r;
+}
+
 static enum cps_return cps(struct uns_ctr *prevstack,
                            struct uns_ctr *readstack)
 {
@@ -1762,6 +1807,8 @@ static enum cps_return cps(struct uns_ctr *prevstack,
 		r = cps_exec(prevstack, readstack);
 	} else if (strcmp(cmd, "cps-list") == 0) {
 		r = cps_list(prevstack, readstack);
+	} else if (strcmp(cmd, "swap2") == 0) {
+		r = cps_swap(prevstack, 2, readstack);
 	} else {
 		r = CPS_INVALID_CMD;
 	}