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experimental/lib-fold-attr

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adding useful function foldAttr which behave like fold on attr values grouped by name
(without assertions now)

Signed-off-by: Marc Weber <marco-oweber@gmx.de>
This commit is contained in:
Marc Weber 2012-08-28 14:40:24 +02:00
parent def452861d
commit aa583c8cf4
2 changed files with 19 additions and 1 deletions
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13
pkgs/lib/attrsets.nix
View File

@ -5,7 +5,8 @@ with {
inherit (import ./trivial.nix) or;
inherit (import ./default.nix) fold;
inherit (import ./strings.nix) concatStringsSep;
inherit (import ./lists.nix) concatMap concatLists;
inherit (import ./lists.nix) concatMap concatLists all;
inherit (import ./misc.nix) maybeAttr;
};
rec {
@ -78,6 +79,16 @@ rec {
filterAttrs = pred: set:
listToAttrs (fold (n: ys: let v = getAttr n set; in if pred n v then [(nameValuePair n v)] ++ ys else ys) [] (attrNames set));
/* foldAttrs: apply fold functions to values grouped by key. Eg accumulate values as list:
foldAttrs (n: a: [n] ++ a) [] [{ a = 2; } { a = 3; }]
=> { a = [ 2 3 ]; }
*/
foldAttrs = op: nul: list_of_attrs:
fold (n: a:
fold (name: o:
o // (listToAttrs [{inherit name; value = op (getAttr name n) (maybeAttr name nul a); }])
) a (attrNames n)
) {} list_of_attrs;
/* Recursively collect sets that verify a given predicate named `pred'
from the set `attrs'. The recursion is stopped when the predicate is

7
pkgs/lib/tests.nix
View File

@ -58,6 +58,13 @@ runTests {
([ 1 2 3 ] == (take 4 [ 1 2 3 ]))
];
testFoldAttrs = {
expr = foldAttrs (n: a: [n] ++ a) [] [
{ a = 2; b = 7; }
{ a = 3; c = 8; }
];
expected = { a = [ 2 3 ]; b = [7]; c = [8];};
};
testOverridableDelayableArgsTest = {
expr =