From: Simon Forman <sforman@hushmail.com>
Date: Fri, 24 Dec 2021 03:12:17 +0000 (-0800)
Subject: Functional-style remove function.
X-Git-Url: http://git.osdn.net/view?p=joypy%2FThun.git;a=commitdiff_plain;h=cc8d15ed84ec4186aadfea15107e3f7aeafd3e6b

Functional-style remove function.
---

diff --git a/joy/library.py b/joy/library.py
index 800ff3b..93455ab 100644
--- a/joy/library.py
+++ b/joy/library.py
@@ -416,7 +416,8 @@ def sum_(S):
 def remove(S):
     '''
     Expects an item on the stack and a quote under it and removes that item
-    from the the quote.  The item is only removed once.
+    from the the quote.  The item is only removed once.  If the list is
+    empty or the item isn't in the list then the list is unchanged.
     ::
 
            [1 2 3 1] 1 remove
@@ -424,10 +425,14 @@ def remove(S):
              [2 3 1]
 
     '''
-    (tos, (second, stack)) = S
-    l = list(iter_stack(second))
-    l.remove(tos)
-    return list_to_stack(l), stack
+    (item, (quote, stack)) = S
+    return _remove(item, quote), stack
+
+
+def _remove(item, quote):
+    try: head, tail = quote
+    except ValueError: return quote
+    return tail if head == item else (head, _remove(item, tail))
 
 
 @inscribe