lib: implement compare, splitByAndCompare, and compareLists

This commit is contained in:
Jan Malakhovski 2017-12-07 21:26:30 +00:00
parent aeb32cf187
commit bccab965b9
3 changed files with 52 additions and 3 deletions

View file

@ -56,7 +56,7 @@ let
replaceStrings seq stringLength sub substring tail;
inherit (trivial) id const concat or and boolToString mergeAttrs
flip mapNullable inNixShell min max importJSON warn info
nixpkgsVersion mod;
nixpkgsVersion mod compare splitByAndCompare;
inherit (fixedPoints) fix fix' extends composeExtensions
makeExtensible makeExtensibleWithCustomName;
@ -71,8 +71,8 @@ let
inherit (lists) singleton foldr fold foldl foldl' imap0 imap1
concatMap flatten remove findSingle findFirst any all count
optional optionals toList range partition zipListsWith zipLists
reverseList listDfs toposort sort take drop sublist last init
crossLists unique intersectLists subtractLists
reverseList listDfs toposort sort compareLists take drop sublist
last init crossLists unique intersectLists subtractLists
mutuallyExclusive;
inherit (strings) concatStrings concatMapStrings concatImapStrings
intersperse concatStringsSep concatMapStringsSep

View file

@ -385,6 +385,30 @@ rec {
if len < 2 then list
else (sort strictLess pivot.left) ++ [ first ] ++ (sort strictLess pivot.right));
/* Compare two lists element-by-element.
Example:
compareLists compare [] []
=> 0
compareLists compare [] [ "a" ]
=> -1
compareLists compare [ "a" ] []
=> 1
compareLists compare [ "a" "b" ] [ "a" "c" ]
=> 1
*/
compareLists = cmp: a: b:
if a == []
then if b == []
then 0
else -1
else if b == []
then 1
else let rel = cmp (head a) (head b); in
if rel == 0
then compareLists cmp (tail a) (tail b)
else rel;
/* Return the first (at most) N elements of a list.
Example:

View file

@ -81,6 +81,31 @@ rec {
*/
mod = base: int: base - (int * (builtins.div base int));
/* C-style comparisons
a < b => -1
a == b => 0
a > b => 1
*/
compare = a: b:
if a < b
then -1
else if a > b
then 1
else 0;
/* Split type into two subtypes by predicate `p`, assume
forall x y . x < y if p x == true && p y == false
compare elements of the same subtype with `yes` and `no`
comparisons respectively.
*/
splitByAndCompare = p: yes: no: a: b:
if p a
then if p b then yes a b else -1
else if p b then 1 else no a b;
/* Reads a JSON file. */
importJSON = path:
builtins.fromJSON (builtins.readFile path);