diff options
Diffstat (limited to 'lib/lists.nix')
-rw-r--r-- | lib/lists.nix | 28 |
1 files changed, 27 insertions, 1 deletions
diff --git a/lib/lists.nix b/lib/lists.nix index c3e889644b3e..3e058b3f1aef 100644 --- a/lib/lists.nix +++ b/lib/lists.nix @@ -3,7 +3,7 @@ { lib }: let inherit (lib.strings) toInt; - inherit (lib.trivial) compare min; + inherit (lib.trivial) compare min id; inherit (lib.attrsets) mapAttrs; in rec { @@ -663,6 +663,32 @@ rec { else if start + count > len then len - start else count); + /* The common prefix of two lists. + + Type: commonPrefix :: [a] -> [a] -> [a] + + Example: + commonPrefix [ 1 2 3 4 5 6 ] [ 1 2 4 8 ] + => [ 1 2 ] + commonPrefix [ 1 2 3 ] [ 1 2 3 4 5 ] + => [ 1 2 3 ] + commonPrefix [ 1 2 3 ] [ 4 5 6 ] + => [ ] + */ + commonPrefix = + list1: + list2: + let + # Zip the lists together into a list of booleans whether each element matches + matchings = zipListsWith (fst: snd: fst != snd) list1 list2; + # Find the first index where the elements don't match, + # which will then also be the length of the common prefix. + # If all elements match, we fall back to the length of the zipped list, + # which is the same as the length of the smaller list. + commonPrefixLength = findFirstIndex id (length matchings) matchings; + in + take commonPrefixLength list1; + /* Return the last element of a list. This function throws an error if the list is empty. |