mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-10-31 22:51:22 +00:00
Merge pull request #243520 from tweag/lib.lists.commonPrefix
`lib.lists.{findFirstIndex,commonPrefix}`: init
This commit is contained in:
commit
bd74cdfb2e
@ -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 {
|
||||
@ -180,18 +180,18 @@ rec {
|
||||
else if len != 1 then multiple
|
||||
else head found;
|
||||
|
||||
/* Find the first element in the list matching the specified
|
||||
/* Find the first index in the list matching the specified
|
||||
predicate or return `default` if no such element exists.
|
||||
|
||||
Type: findFirst :: (a -> bool) -> a -> [a] -> a
|
||||
Type: findFirstIndex :: (a -> Bool) -> b -> [a] -> (Int | b)
|
||||
|
||||
Example:
|
||||
findFirst (x: x > 3) 7 [ 1 6 4 ]
|
||||
=> 6
|
||||
findFirst (x: x > 9) 7 [ 1 6 4 ]
|
||||
=> 7
|
||||
findFirstIndex (x: x > 3) null [ 0 6 4 ]
|
||||
=> 1
|
||||
findFirstIndex (x: x > 9) null [ 0 6 4 ]
|
||||
=> null
|
||||
*/
|
||||
findFirst =
|
||||
findFirstIndex =
|
||||
# Predicate
|
||||
pred:
|
||||
# Default value to return
|
||||
@ -229,7 +229,33 @@ rec {
|
||||
if resultIndex < 0 then
|
||||
default
|
||||
else
|
||||
elemAt list resultIndex;
|
||||
resultIndex;
|
||||
|
||||
/* Find the first element in the list matching the specified
|
||||
predicate or return `default` if no such element exists.
|
||||
|
||||
Type: findFirst :: (a -> bool) -> a -> [a] -> a
|
||||
|
||||
Example:
|
||||
findFirst (x: x > 3) 7 [ 1 6 4 ]
|
||||
=> 6
|
||||
findFirst (x: x > 9) 7 [ 1 6 4 ]
|
||||
=> 7
|
||||
*/
|
||||
findFirst =
|
||||
# Predicate
|
||||
pred:
|
||||
# Default value to return
|
||||
default:
|
||||
# Input list
|
||||
list:
|
||||
let
|
||||
index = findFirstIndex pred null list;
|
||||
in
|
||||
if index == null then
|
||||
default
|
||||
else
|
||||
elemAt list index;
|
||||
|
||||
/* Return true if function `pred` returns true for at least one
|
||||
element of `list`.
|
||||
@ -637,6 +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.
|
||||
|
@ -500,6 +500,39 @@ runTests {
|
||||
expected = { a = [ 2 3 ]; b = [7]; c = [8];};
|
||||
};
|
||||
|
||||
testListCommonPrefixExample1 = {
|
||||
expr = lists.commonPrefix [ 1 2 3 4 5 6 ] [ 1 2 4 8 ];
|
||||
expected = [ 1 2 ];
|
||||
};
|
||||
testListCommonPrefixExample2 = {
|
||||
expr = lists.commonPrefix [ 1 2 3 ] [ 1 2 3 4 5 ];
|
||||
expected = [ 1 2 3 ];
|
||||
};
|
||||
testListCommonPrefixExample3 = {
|
||||
expr = lists.commonPrefix [ 1 2 3 ] [ 4 5 6 ];
|
||||
expected = [ ];
|
||||
};
|
||||
testListCommonPrefixEmpty = {
|
||||
expr = lists.commonPrefix [ ] [ 1 2 3 ];
|
||||
expected = [ ];
|
||||
};
|
||||
testListCommonPrefixSame = {
|
||||
expr = lists.commonPrefix [ 1 2 3 ] [ 1 2 3 ];
|
||||
expected = [ 1 2 3 ];
|
||||
};
|
||||
testListCommonPrefixLazy = {
|
||||
expr = lists.commonPrefix [ 1 ] [ 1 (abort "lib.lists.commonPrefix shouldn't evaluate this")];
|
||||
expected = [ 1 ];
|
||||
};
|
||||
# This would stack overflow if `commonPrefix` were implemented using recursion
|
||||
testListCommonPrefixLong =
|
||||
let
|
||||
longList = genList (n: n) 100000;
|
||||
in {
|
||||
expr = lists.commonPrefix longList longList;
|
||||
expected = longList;
|
||||
};
|
||||
|
||||
testSort = {
|
||||
expr = sort builtins.lessThan [ 40 2 30 42 ];
|
||||
expected = [2 30 40 42];
|
||||
@ -530,45 +563,55 @@ runTests {
|
||||
expected = false;
|
||||
};
|
||||
|
||||
testFindFirstExample1 = {
|
||||
expr = findFirst (x: x > 3) 7 [ 1 6 4 ];
|
||||
expected = 6;
|
||||
testFindFirstIndexExample1 = {
|
||||
expr = lists.findFirstIndex (x: x > 3) (abort "index found, so a default must not be evaluated") [ 1 6 4 ];
|
||||
expected = 1;
|
||||
};
|
||||
|
||||
testFindFirstExample2 = {
|
||||
expr = findFirst (x: x > 9) 7 [ 1 6 4 ];
|
||||
expected = 7;
|
||||
testFindFirstIndexExample2 = {
|
||||
expr = lists.findFirstIndex (x: x > 9) "a very specific default" [ 1 6 4 ];
|
||||
expected = "a very specific default";
|
||||
};
|
||||
|
||||
testFindFirstEmpty = {
|
||||
expr = findFirst (abort "when the list is empty, the predicate is not needed") null [];
|
||||
testFindFirstIndexEmpty = {
|
||||
expr = lists.findFirstIndex (abort "when the list is empty, the predicate is not needed") null [];
|
||||
expected = null;
|
||||
};
|
||||
|
||||
testFindFirstSingleMatch = {
|
||||
expr = findFirst (x: x == 5) null [ 5 ];
|
||||
expected = 5;
|
||||
testFindFirstIndexSingleMatch = {
|
||||
expr = lists.findFirstIndex (x: x == 5) null [ 5 ];
|
||||
expected = 0;
|
||||
};
|
||||
|
||||
testFindFirstSingleDefault = {
|
||||
expr = findFirst (x: false) null [ (abort "if the predicate doesn't access the value, it must not be evaluated") ];
|
||||
testFindFirstIndexSingleDefault = {
|
||||
expr = lists.findFirstIndex (x: false) null [ (abort "if the predicate doesn't access the value, it must not be evaluated") ];
|
||||
expected = null;
|
||||
};
|
||||
|
||||
testFindFirstNone = {
|
||||
expr = builtins.tryEval (findFirst (x: x == 2) null [ 1 (throw "the last element must be evaluated when there's no match") ]);
|
||||
testFindFirstIndexNone = {
|
||||
expr = builtins.tryEval (lists.findFirstIndex (x: x == 2) null [ 1 (throw "the last element must be evaluated when there's no match") ]);
|
||||
expected = { success = false; value = false; };
|
||||
};
|
||||
|
||||
# Makes sure that the implementation doesn't cause a stack overflow
|
||||
testFindFirstBig = {
|
||||
expr = findFirst (x: x == 1000000) null (range 0 1000000);
|
||||
testFindFirstIndexBig = {
|
||||
expr = lists.findFirstIndex (x: x == 1000000) null (range 0 1000000);
|
||||
expected = 1000000;
|
||||
};
|
||||
|
||||
testFindFirstLazy = {
|
||||
expr = findFirst (x: x == 1) 7 [ 1 (abort "list elements after the match must not be evaluated") ];
|
||||
expected = 1;
|
||||
testFindFirstIndexLazy = {
|
||||
expr = lists.findFirstIndex (x: x == 1) null [ 1 (abort "list elements after the match must not be evaluated") ];
|
||||
expected = 0;
|
||||
};
|
||||
|
||||
testFindFirstExample1 = {
|
||||
expr = lists.findFirst (x: x > 3) 7 [ 1 6 4 ];
|
||||
expected = 6;
|
||||
};
|
||||
|
||||
testFindFirstExample2 = {
|
||||
expr = lists.findFirst (x: x > 9) 7 [ 1 6 4 ];
|
||||
expected = 7;
|
||||
};
|
||||
|
||||
# ATTRSETS
|
||||
|
Loading…
Reference in New Issue
Block a user