From ce6d4070a616554c0ca6948338b47cb192f7306a Mon Sep 17 00:00:00 2001
From: Shea Levy <shea@shealevy.com>
Date: Wed, 19 Dec 2012 22:49:21 -0500
Subject: [PATCH] Add a 'functionTo x' type.

This is mainly to for the 'merge' concept, but I made a guess as to what
iter and fold would mean for functions.
---
 pkgs/lib/types.nix | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/pkgs/lib/types.nix b/pkgs/lib/types.nix
index 38ae7b43630..b99fe5a5771 100644
--- a/pkgs/lib/types.nix
+++ b/pkgs/lib/types.nix
@@ -176,6 +176,19 @@ rec {
       fold = op: nul: v: if v == null then nul else elemType.fold op nul v;
     };
 
+    functionTo = elemType: mkOptionType {
+      name = "function that evaluates to a(n) ${elemType.name}";
+      check = lib.traceValIfNot builtins.isFunction;
+      merge = fns:
+        args: elemType.merge (map (fn: fn args) fns)
+      # These are guesses, I don't fully understand iter, fold, delayOnGlobalEval
+      iter = f: path: v:
+        args: elemType.iter f path (v args);
+      fold = op: nul: v:
+        args: elemType.fold op nul (v args);
+      inherit (elemType) hasOptions delayOnGlobalEval;
+    };
+
     # !!! this should be a type constructor that takes the options as
     # an argument.
     optionSet = mkOptionType {