From 85d3fd3e3cf6a7cd2ec361b3bb996f8587f8c34c Mon Sep 17 00:00:00 2001
From: Nicolas Pierron <nicolas.b.pierron@gmail.com>
Date: Wed, 27 Apr 2011 18:41:34 +0000
Subject: [PATCH] lists: Add imap function to iterate over a list with the
 index of each element.

svn path=/nixpkgs/trunk/; revision=27013
---
 pkgs/lib/lists.nix | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pkgs/lib/lists.nix b/pkgs/lib/lists.nix
index a843addaf9e5..6adda85a087e 100644
--- a/pkgs/lib/lists.nix
+++ b/pkgs/lib/lists.nix
@@ -1,7 +1,7 @@
 # General list operations.
 
 rec {
-  inherit (builtins) head tail isList;
+  inherit (builtins) head tail length isList;
 
 
   # Create a list consisting of a single element.  `singleton x' is
@@ -27,6 +27,10 @@ rec {
     then nul
     else foldl op (op nul (head list)) (tail list);
 
+  # map with index: `imap (i: v: "${v}-${toString i}") ["a" "b"] ==
+  # ["a-1" "b-2"]'
+  imap = f: list:
+    zipListsWith f (range 1 (length list)) list;
 
   # Concatenate a list of lists.
   concatLists = fold (x: y: x ++ y) [];