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Add 'collect' a function which recursively collects all attribute values verifying a predicate.

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svn path=/nixpkgs/trunk/; revision=15936
This commit is contained in:
Nicolas Pierron 2009-06-11 16:03:33 +00:00
parent b32002c3a3
commit 0f6a67814a
1 changed files with 26 additions and 0 deletions
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26
pkgs/lib/attrsets.nix
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@ -4,6 +4,7 @@ with {
inherit (builtins) head tail isString;
inherit (import ./default.nix) fold;
inherit (import ./strings.nix) concatStringsSep;
inherit (import ./lists.nix) concatMap;
};
rec {
@ -66,6 +67,31 @@ rec {
catAttrs = attr: l: fold (s: l: if hasAttr attr s then [(getAttr attr s)] ++ l else l) [] l;
/* Recursively collect sets that verify a given predicate named `pred'
from the set `attrs'. The recursion is stopped when the predicate is
verified.
Type:
collect ::
(AttrSet -> Bool) -> AttrSet -> AttrSet
Example:
collect builtins.isList { a = { b = ["b"]; }; c = [1]; }
=> ["b" 1]
collect (x: x ? outPath)
{ a = { outPath = "a/"; }; b = { outPath = "b/"; }; }
=> [{ outPath = "a/"; } { outPath = "b/"; }]
*/
collect = pred: attrs:
if pred attrs then
[ attrs ]
else if builtins.isAttrs attrs then
concatMap (collect pred) (attrValues attrs)
else
[];
/* Utility function that creates a {name, value} pair as expected by
builtins.listToAttrs. */
nameValuePair = name: value: { inherit name value; };