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lib.lists.commonPrefix: init

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This commit is contained in:
Silvan Mosberger 2023-07-14 19:26:08 +02:00
parent 53dcfd24ad
commit 7f61b01600
2 changed files with 60 additions and 1 deletions
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28
lib/lists.nix
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@ -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.