From bccab965b9226e7d515e1ee1cdf47bb32d1df63d Mon Sep 17 00:00:00 2001
From: Jan Malakhovski <oxij@oxij.org>
Date: Thu, 7 Dec 2017 21:26:30 +0000
Subject: lib: implement `compare`, `splitByAndCompare`, and `compareLists`

---
 lib/lists.nix | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

(limited to 'lib/lists.nix')

diff --git a/lib/lists.nix b/lib/lists.nix
index 8f67c6bb0ca3..f7e09040a5aa 100644
--- a/lib/lists.nix
+++ b/lib/lists.nix
@@ -385,6 +385,30 @@ rec {
       if len < 2 then list
       else (sort strictLess pivot.left) ++  [ first ] ++  (sort strictLess pivot.right));
 
+  /* Compare two lists element-by-element.
+
+     Example:
+       compareLists compare [] []
+       => 0
+       compareLists compare [] [ "a" ]
+       => -1
+       compareLists compare [ "a" ] []
+       => 1
+       compareLists compare [ "a" "b" ] [ "a" "c" ]
+       => 1
+  */
+  compareLists = cmp: a: b:
+    if a == []
+    then if b == []
+         then 0
+         else -1
+    else if b == []
+         then 1
+         else let rel = cmp (head a) (head b); in
+              if rel == 0
+              then compareLists cmp (tail a) (tail b)
+              else rel;
+
   /* Return the first (at most) N elements of a list.
 
      Example:
-- 
cgit 1.4.1