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* Function `findSingle' for looking up values in dictionary-like

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svn path=/nixpkgs/trunk/; revision=7446
This commit is contained in:
Eelco Dolstra 2006-12-21 00:09:40 +00:00
parent fe30bcab94
commit e726057b32
1 changed files with 10 additions and 0 deletions
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pkgs/lib/default.nix
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@ -61,6 +61,16 @@ rec {
fold (x: y: if pred x then [x] ++ y else y) [] list; fold (x: y: if pred x then [x] ++ y else y) [] list;
# Find the sole element in the list matching the specified
# predicate, or returns the default value.
findSingle = pred: default: list:
let found = filter pred list;
in if found == [] then default
else if tail found != [] then
abort "Multiple elements match predicate in findSingle."
else head found;
# Return true if each element of a list is equal, false otherwise. # Return true if each element of a list is equal, false otherwise.
eqLists = xs: ys: eqLists = xs: ys:
if xs == [] && ys == [] then true if xs == [] && ys == [] then true