From 864d1c6fe182661a7bd7d4eda928f8a19318b651 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 9 Jun 2021 23:35:38 -0700
Subject: reduce-left: rewrite using seq_iter.

* lib.c (reduce_left): Use sequence iteration instead of list
operations.

* txr.1: Add a note to the documentation.
---
 lib.c            | 16 ++++++++++------
 tests/012/seq.tl | 10 ++++++++++
 txr.1            | 12 ++++++++++++
 3 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/lib.c b/lib.c
index 9e3827d7..9a4f4533 100644
--- a/lib.c
+++ b/lib.c
@@ -7902,22 +7902,26 @@ val funcall4(val fun, val arg1, val arg2, val arg3, val arg4)
   wrongargs(fun);
 }
 
-val reduce_left(val fun, val list, val init, val key)
+val reduce_left(val fun, val seq, val init, val key)
 {
+  val self = lit("reduce-left");
+  seq_iter_t item_iter;
+  val item;
+
   if (null_or_missing_p(key))
     key = identity_f;
 
-  list = nullify(list);
+  seq_iter_init(self, &item_iter, seq);
 
   if (missingp(init)) {
-    if (list)
-      init = funcall1(key, pop(&list));
+    if (seq_get(&item_iter, &item))
+      init = funcall1(key, item);
     else
       return funcall(fun);
   }
 
-  for (; list; list = cdr(list))
-    init = funcall2(fun, init, funcall1(key, car(list)));
+  while (seq_get(&item_iter, &item))
+    init = funcall2(fun, init, funcall1(key, item));
 
   return init;
 }
diff --git a/tests/012/seq.tl b/tests/012/seq.tl
index 49d4046b..95ba7b6e 100644
--- a/tests/012/seq.tl
+++ b/tests/012/seq.tl
@@ -72,3 +72,13 @@
                   (lambda (. args) (/ (sum args) 5))
                   #(4 7 9 13 5 1 6 11 10 3 8)]
       #(4.0 6.6 7.6 7.0 6.8 7.2 6.6 6.2 7.6 6.4 4.2))
+
+(mtest
+  [reduce-left + () 0] 0
+  [reduce-left + ()] 0
+  [reduce-left cons ()] :error
+  [reduce-left cons '(1)] 1
+  [reduce-left cons #(1)] 1
+  [reduce-left cons #(1) : (op * 10)] 10
+  [reduce-left cons #(1) 2 (op * 10)] (2 . 10)
+  [reduce-left cons #(2 3) 10 (op * 10)] ((10 . 20) . 30))
diff --git a/txr.1 b/txr.1
index 80d28239..1a172ca7 100644
--- a/txr.1
+++ b/txr.1
@@ -34308,6 +34308,18 @@ and
 to a single value by the repeated application of
 .metn binary-function .
 
+In the case of
+.codn reduce-left ,
+the
+.meta list
+argument required to be an object which is iterable according to the
+.code iter-begin
+function. The
+.code reduce-right
+function treats the
+.meta list
+argument using list operations.
+
 An effective list of operands is formed by combining
 .meta list
 and
-- 
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