From 7ef915ebc88f7784cdec5a9917818cbdfe1a76c4 Mon Sep 17 00:00:00 2001
From: Marc Weber <marco-oweber@gmx.de>
Date: Tue, 8 Dec 2009 21:47:14 +0000
Subject: [PATCH] nixpkgs lib: adding haskell's take

svn path=/nixpkgs/trunk/; revision=18848
---
 pkgs/lib/lists.nix | 6 ++++++
 pkgs/lib/tests.nix | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/pkgs/lib/lists.nix b/pkgs/lib/lists.nix
index 3a5ed2628de8..4359662da27b 100644
--- a/pkgs/lib/lists.nix
+++ b/pkgs/lib/lists.nix
@@ -161,4 +161,10 @@ rec {
     in
       qs list [];
 
+
+  # haskell's take:  take 2 [1 2 3 4]  yields  [1 2] 
+  take = count: list:
+    if list == [] || count == 0 then []
+    else [ (head list) ] ++ take (builtins.sub count 1) (tail list);
+
 }
diff --git a/pkgs/lib/tests.nix b/pkgs/lib/tests.nix
index c5476cbc18c6..9aa04f623608 100644
--- a/pkgs/lib/tests.nix
+++ b/pkgs/lib/tests.nix
@@ -61,6 +61,15 @@ runTests {
     expected = true;
   };
 
+  testTake = testAllTrue [
+    ([] == (take 0 [  1 2 3 ]))
+    ([1] == (take 1 [  1 2 3 ]))
+    ([ 1 2 ] == (take 2 [  1 2 3 ]))
+    ([ 1 2 3 ] == (take 3 [  1 2 3 ]))
+    ([ 1 2 3 ] == (take 4 [  1 2 3 ]))
+  ];
+
+
   testOverridableDelayableArgsTest = {
     expr = 
       let res1 = defaultOverridableDelayableArgs id {};