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added examples for composedArgsAndFun, introducing setAttrMerge

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svn path=/nixpkgs/trunk/; revision=13193
This commit is contained in:
Marc Weber 2008-11-04 21:40:51 +00:00
parent b9173d8755
commit 2bf82b4470
1 changed files with 24 additions and 6 deletions
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28
pkgs/lib/default.nix
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@ -41,11 +41,23 @@ rec {
f (defaultMerge x y);
foldArgs = merger: f: init: x:
let arg=(merger init (defaultMergeArg init x)); in
(f arg) // {
passthru = (getAttr ["passthru"] {} arg) // {
function = foldArgs merger f arg;
};
};
# now add the function with composed args already applied to the final attrs
setAttrMerge "passthru" {} (f arg) ( x : x // { function = foldArgs merger f arg; } );
# rec { # an example of how composedArgsAndFun can be used
# a = composedArgsAndFun (x : x) { a = ["2"]; meta = { d = "bar";}; };
# # meta.d will be lost ! It's your task to preserve it (eg using a merge function)
# b = a.passthru.function { a = [ "3" ]; meta = { d2 = "bar2";}; };
# # instead of passing/ overriding values you can use a merge function:
# c = b.passthru.function ( x: { a = x.a ++ ["4"]; }); # consider using (maybeAttr "a" [] x)
# }
# result:
# {
# a = { a = ["2"]; meta = { d = "bar"; }; passthru = { function = .. }; };
# b = { a = ["3"]; meta = { d2 = "bar2"; }; passthru = { function = .. }; };
# c = { a = ["3" "4"]; meta = { d2 = "bar2"; }; passthru = { function = .. }; };
# # c2 is equal to c
# }
composedArgsAndFun = f: foldArgs defaultMerge f {};
# example a = pairMap (x : y : x + y) ["a" "b" "c" "d"];
@ -526,6 +538,12 @@ rec {
# adds / replaces an attribute of an attribute set
setAttr = set : name : v : set // (nvs name v);
# setAttrMerge (similar to mergeAttrsWithFunc but only merges the values of a particular name)
# setAttrMerge "a" [] { a = [2];} (x : x ++ [3]) -> { a = [2 3]; }
# setAttrMerge "a" [] { } (x : x ++ [3]) -> { a = [ 3]; }
setAttrMerge = name : default : attrs : f :
setAttr attrs name (f (maybeAttr name default attrs));
# iterates over a list of attributes collecting the attribute attr if it exists
catAttrs = attr : l : fold ( s : l : if (hasAttr attr s) then [(builtins.getAttr attr s)] ++ l else l) [] l;