From 19456350b81fcc95d09468989c34a20fb1ad9bc9 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Thu, 20 Jun 2024 00:11:27 -0700
Subject: combi: fix broken k 0 edge cases for sequences.

* combi.c (rperm, comb, rcomb): In the default
case for generic sequences, check k, like
in the other cases and return the special
case result.

* tests/015/comb.tl: New tests.
---
 combi.c           |  8 ++++++++
 tests/015/comb.tl | 10 ++++++++++
 2 files changed, 18 insertions(+)

diff --git a/combi.c b/combi.c
index 1eaade29..2b55ee08 100644
--- a/combi.c
+++ b/combi.c
@@ -471,6 +471,8 @@ val rperm(val seq, val k)
       return cons(string(L""), nil);
     return rperm_str(seq, k);
   default:
+    if (zerop(k))
+      return cons(make_like(nil, seq), nil);
     return rperm_seq(seq, k);
   }
 }
@@ -748,6 +750,10 @@ val comb(val seq, val k)
         return nil;
       return comb_hash(seq, k);
     }
+    if (k == zero)
+      return cons(make_like(nil, seq), nil);
+    if (gt(k, length(seq)))
+      return nil;
     return comb_seq(seq, k);
   }
 }
@@ -879,6 +885,8 @@ val rcomb(val seq, val k)
       return cons(string(L""), nil);
     return rcomb_str(seq, k);
   default:
+    if (k == zero)
+      return cons(make_like(nil, seq), nil);
     return rcomb_seq(seq, k);
   }
 }
diff --git a/tests/015/comb.tl b/tests/015/comb.tl
index 9973e94d..70aa9dd3 100644
--- a/tests/015/comb.tl
+++ b/tests/015/comb.tl
@@ -441,3 +441,13 @@
   (rperm "a".."c" 2) (("a" "a") ("a" "b") ("a" "c")
                       ("b" "a") ("b" "b") ("b" "c")
                       ("c" "a") ("c" "b") ("c" "c")))
+
+(mtest
+  (perm '(1 2 3) 0) (nil)
+  (rperm '(1 2 3) 0) (nil)
+  (comb '(1 2 3) 0) (nil)
+  (rcomb '(1 2 3) 0) (nil)
+  (perm 1..4 0) (nil)
+  (rperm 1..4 0) (nil)
+  (comb 1..4 0) (nil)
+  (rcomb 1..4 0) (nil))
-- 
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