Use builtins.genList

This fixes the quadratic complexity of functions like imap.
This commit is contained in:
Eelco Dolstra 2015-07-28 17:31:43 +02:00
parent 273d9ffd6a
commit 5976d393fb

View file

@ -4,7 +4,7 @@ with import ./trivial.nix;
rec {
inherit (builtins) head tail length isList elemAt concatLists filter elem;
inherit (builtins) head tail length isList elemAt concatLists filter elem genList;
# Create a list consisting of a single element. `singleton x' is
@ -42,16 +42,20 @@ rec {
foldl' = builtins.foldl' or foldl;
# map with index: `imap (i: v: "${v}-${toString i}") ["a" "b"] ==
# ["a-1" "b-2"]'
imap = f: list:
let
len = length list;
imap' = n:
if n == len
then []
else [ (f (n + 1) (elemAt list n)) ] ++ imap' (n + 1);
in imap' 0;
# Map with index: `imap (i: v: "${v}-${toString i}") ["a" "b"] ==
# ["a-1" "b-2"]'. FIXME: why does this start to count at 1?
imap =
if builtins ? genList then
f: list: genList (n: f (n + 1) (elemAt list n)) (length list)
else
f: list:
let
len = length list;
imap' = n:
if n == len
then []
else [ (f (n + 1) (elemAt list n)) ] ++ imap' (n + 1);
in imap' 0;
# Map and concatenate the result.
@ -120,10 +124,17 @@ rec {
# Return a list of integers from `first' up to and including `last'.
range = first: last:
if last < first
then []
else [first] ++ range (first + 1) last;
range =
if builtins ? genList then
first: last:
if first > last
then []
else genList (n: first + n) (last - first + 1)
else
first: last:
if last < first
then []
else [first] ++ range (first + 1) last;
# Partition the elements of a list in two lists, `right' and
@ -136,23 +147,29 @@ rec {
) { right = []; wrong = []; };
zipListsWith = f: fst: snd:
let
len1 = length fst;
len2 = length snd;
len = if len1 < len2 then len1 else len2;
zipListsWith' = n:
if n != len then
[ (f (elemAt fst n) (elemAt snd n)) ]
++ zipListsWith' (n + 1)
else [];
in zipListsWith' 0;
zipListsWith =
if builtins ? genList then
f: fst: snd: genList (n: f (elemAt fst n) (elemAt snd n)) (min (length fst) (length snd))
else
f: fst: snd:
let
len = min (length fst) (length snd);
zipListsWith' = n:
if n != len then
[ (f (elemAt fst n) (elemAt snd n)) ]
++ zipListsWith' (n + 1)
else [];
in zipListsWith' 0;
zipLists = zipListsWith (fst: snd: { inherit fst snd; });
# Reverse the order of the elements of a list. FIXME: O(n^2)!
reverseList = fold (e: acc: acc ++ [ e ]) [];
# Reverse the order of the elements of a list.
reverseList =
if builtins ? genList then
xs: let l = length xs; in genList (n: elemAt xs (l - n - 1)) l
else
fold (e: acc: acc ++ [ e ]) [];
# Sort a list based on a comparator function which compares two
@ -177,27 +194,46 @@ rec {
# Return the first (at most) N elements of a list.
take = count: list:
let
len = length list;
take' = n:
if n == len || n == count
then []
else
[ (elemAt list n) ] ++ take' (n + 1);
in take' 0;
take =
if builtins ? genList then
count: sublist 0 count
else
count: list:
let
len = length list;
take' = n:
if n == len || n == count
then []
else
[ (elemAt list n) ] ++ take' (n + 1);
in take' 0;
# Remove the first (at most) N elements of a list.
drop = count: list:
let
len = length list;
drop' = n:
if n == -1 || n < count
then []
else
drop' (n - 1) ++ [ (elemAt list n) ];
in drop' (len - 1);
drop =
if builtins ? genList then
count: list: sublist count (length list) list
else
count: list:
let
len = length list;
drop' = n:
if n == -1 || n < count
then []
else
drop' (n - 1) ++ [ (elemAt list n) ];
in drop' (len - 1);
# Return a list consisting of at most count elements of list,
# starting at index start.
sublist = start: count: list:
let len = length list; in
genList
(n: elemAt list (n + start))
(if start >= len then 0
else if start + count > len then len - start
else count);
# Return the last element of a list.
@ -211,9 +247,11 @@ rec {
deepSeqList = xs: y: if any (x: deepSeq x false) xs then y else y;
crossLists = f: foldl (fs: args: concatMap (f: map f args) fs) [f];
# Remove duplicate elements from the list
# Remove duplicate elements from the list. O(n^2) complexity.
unique = list:
if list == [] then
[]
@ -223,9 +261,12 @@ rec {
xs = unique (drop 1 list);
in [x] ++ remove x xs;
# Intersects list 'e' and another list
# Intersects list 'e' and another list. O(nm) complexity.
intersectLists = e: filter (x: elem x e);
# Subtracts list 'e' from another list
# Subtracts list 'e' from another list. O(nm) complexity.
subtractLists = e: filter (x: !(elem x e));
}