Merge pull request #243511 from tweag/lib.lists.hasPrefix
`lib.lists.{hasPrefix,removePrefix}`: init
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commit
87c5a6a84f
2 changed files with 72 additions and 0 deletions
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@ -638,6 +638,40 @@ rec {
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# Input list
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list: sublist count (length list) list;
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/* Whether the first list is a prefix of the second list.
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Type: hasPrefix :: [a] -> [a] -> bool
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Example:
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hasPrefix [ 1 2 ] [ 1 2 3 4 ]
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=> true
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hasPrefix [ 0 1 ] [ 1 2 3 4 ]
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=> false
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*/
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hasPrefix =
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list1:
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list2:
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take (length list1) list2 == list1;
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/* Remove the first list as a prefix from the second list.
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Error if the first list isn't a prefix of the second list.
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Type: removePrefix :: [a] -> [a] -> [a]
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Example:
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removePrefix [ 1 2 ] [ 1 2 3 4 ]
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=> [ 3 4 ]
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removePrefix [ 0 1 ] [ 1 2 3 4 ]
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=> <error>
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*/
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removePrefix =
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list1:
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list2:
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if hasPrefix list1 list2 then
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drop (length list1) list2
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else
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throw "lib.lists.removePrefix: First argument is not a list prefix of the second argument";
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/* Return a list consisting of at most `count` elements of `list`,
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starting at index `start`.
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@ -492,6 +492,44 @@ runTests {
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([ 1 2 3 ] == (take 4 [ 1 2 3 ]))
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];
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testListHasPrefixExample1 = {
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expr = lists.hasPrefix [ 1 2 ] [ 1 2 3 4 ];
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expected = true;
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};
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testListHasPrefixExample2 = {
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expr = lists.hasPrefix [ 0 1 ] [ 1 2 3 4 ];
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expected = false;
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};
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testListHasPrefixLazy = {
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expr = lists.hasPrefix [ 1 ] [ 1 (abort "lib.lists.hasPrefix is not lazy") ];
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expected = true;
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};
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testListHasPrefixEmptyPrefix = {
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expr = lists.hasPrefix [ ] [ 1 2 ];
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expected = true;
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};
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testListHasPrefixEmptyList = {
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expr = lists.hasPrefix [ 1 2 ] [ ];
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expected = false;
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};
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testListRemovePrefixExample1 = {
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expr = lists.removePrefix [ 1 2 ] [ 1 2 3 4 ];
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expected = [ 3 4 ];
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};
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testListRemovePrefixExample2 = {
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expr = (builtins.tryEval (lists.removePrefix [ 0 1 ] [ 1 2 3 4 ])).success;
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expected = false;
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};
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testListRemovePrefixEmptyPrefix = {
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expr = lists.removePrefix [ ] [ 1 2 ];
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expected = [ 1 2 ];
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};
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testListRemovePrefixEmptyList = {
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expr = (builtins.tryEval (lists.removePrefix [ 1 2 ] [ ])).success;
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expected = false;
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};
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testFoldAttrs = {
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expr = foldAttrs (n: a: [n] ++ a) [] [
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{ a = 2; b = 7; }
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