From df8cbba07c7d5e0763b9fd2ee730e93540e8764c Mon Sep 17 00:00:00 2001
From: Justin Lin <justin.sdk@gmail.com>
Date: Sat, 27 Feb 2021 18:38:41 +0800
Subject: [PATCH] add swap

---
 src/util/swap.scad | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 src/util/swap.scad

diff --git a/src/util/swap.scad b/src/util/swap.scad
new file mode 100644
index 00000000..3a3b5238
--- /dev/null
+++ b/src/util/swap.scad
@@ -0,0 +1,13 @@
+function swap(lt, i, j) =
+    let(
+	    leng = len(lt),
+		a = min([i, j]),
+		b = max([i, j])
+	)
+    concat(
+	    a == 0 ? [] : [for(idx = [0:a - 1]) lt[idx]], 
+		[lt[b]], 
+		b - a == 1? [] : [for(idx = [a + 1:b - 1]) lt[idx]], 
+		[lt[a]], 
+		b == leng - 1 ? [] : [for(idx = [b + 1:leng - 1]) lt[idx]]
+	);
\ No newline at end of file