mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-12-11 07:04:28 +00:00
274 lines
7.6 KiB
Nix
274 lines
7.6 KiB
Nix
# General list operations.
|
||
|
||
with import ./trivial.nix;
|
||
|
||
rec {
|
||
|
||
inherit (builtins) head tail length isList elemAt concatLists filter elem genList;
|
||
|
||
|
||
# Create a list consisting of a single element. `singleton x' is
|
||
# sometimes more convenient with respect to indentation than `[x]'
|
||
# when x spans multiple lines.
|
||
singleton = x: [x];
|
||
|
||
|
||
# "Fold" a binary function `op' between successive elements of
|
||
# `list' with `nul' as the starting value, i.e., `fold op nul [x_1
|
||
# x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))'. (This is
|
||
# Haskell's foldr).
|
||
fold = op: nul: list:
|
||
let
|
||
len = length list;
|
||
fold' = n:
|
||
if n == len
|
||
then nul
|
||
else op (elemAt list n) (fold' (n + 1));
|
||
in fold' 0;
|
||
|
||
# Left fold: `fold op nul [x_1 x_2 ... x_n] == op (... (op (op nul
|
||
# x_1) x_2) ... x_n)'.
|
||
foldl = op: nul: list:
|
||
let
|
||
len = length list;
|
||
foldl' = n:
|
||
if n == -1
|
||
then nul
|
||
else op (foldl' (n - 1)) (elemAt list n);
|
||
in foldl' (length list - 1);
|
||
|
||
|
||
# Strict version of foldl.
|
||
foldl' = builtins.foldl' or foldl;
|
||
|
||
|
||
# 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.
|
||
concatMap = f: list: concatLists (map f list);
|
||
|
||
|
||
# Flatten the argument into a single list; that is, nested lists are
|
||
# spliced into the top-level lists. E.g., `flatten [1 [2 [3] 4] 5]
|
||
# == [1 2 3 4 5]' and `flatten 1 == [1]'.
|
||
flatten = x:
|
||
if isList x
|
||
then foldl' (x: y: x ++ (flatten y)) [] x
|
||
else [x];
|
||
|
||
|
||
# Remove elements equal to 'e' from a list. Useful for buildInputs.
|
||
remove = e: filter (x: x != e);
|
||
|
||
|
||
# Find the sole element in the list matching the specified
|
||
# predicate, returns `default' if no such element exists, or
|
||
# `multiple' if there are multiple matching elements.
|
||
findSingle = pred: default: multiple: list:
|
||
let found = filter pred list; len = length found;
|
||
in if len == 0 then default
|
||
else if len != 1 then multiple
|
||
else head found;
|
||
|
||
|
||
# Find the first element in the list matching the specified
|
||
# predicate or returns `default' if no such element exists.
|
||
findFirst = pred: default: list:
|
||
let found = filter pred list;
|
||
in if found == [] then default else head found;
|
||
|
||
|
||
# Return true iff function `pred' returns true for at least element
|
||
# of `list'.
|
||
any = builtins.any or (pred: fold (x: y: if pred x then true else y) false);
|
||
|
||
|
||
# Return true iff function `pred' returns true for all elements of
|
||
# `list'.
|
||
all = builtins.all or (pred: fold (x: y: if pred x then y else false) true);
|
||
|
||
|
||
# Count how many times function `pred' returns true for the elements
|
||
# of `list'.
|
||
count = pred: foldl' (c: x: if pred x then c + 1 else c) 0;
|
||
|
||
|
||
# Return a singleton list or an empty list, depending on a boolean
|
||
# value. Useful when building lists with optional elements
|
||
# (e.g. `++ optional (system == "i686-linux") flashplayer').
|
||
optional = cond: elem: if cond then [elem] else [];
|
||
|
||
|
||
# Return a list or an empty list, dependening on a boolean value.
|
||
optionals = cond: elems: if cond then elems else [];
|
||
|
||
|
||
# If argument is a list, return it; else, wrap it in a singleton
|
||
# list. If you're using this, you should almost certainly
|
||
# reconsider if there isn't a more "well-typed" approach.
|
||
toList = x: if isList x then x else [x];
|
||
|
||
|
||
# Return a list of integers from `first' up to and including `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
|
||
# `wrong', depending on the evaluation of a predicate.
|
||
partition = pred:
|
||
fold (h: t:
|
||
if pred h
|
||
then { right = [h] ++ t.right; wrong = t.wrong; }
|
||
else { right = t.right; wrong = [h] ++ t.wrong; }
|
||
) { right = []; wrong = []; };
|
||
|
||
|
||
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.
|
||
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
|
||
# elements and returns true if the first argument is strictly below
|
||
# the second argument. The returned list is sorted in an increasing
|
||
# order. The implementation does a quick-sort.
|
||
sort = builtins.sort or (
|
||
strictLess: list:
|
||
let
|
||
len = length list;
|
||
first = head list;
|
||
pivot' = n: acc@{ left, right }: let el = elemAt list n; next = pivot' (n + 1); in
|
||
if n == len
|
||
then acc
|
||
else if strictLess first el
|
||
then next { inherit left; right = [ el ] ++ right; }
|
||
else
|
||
next { left = [ el ] ++ left; inherit right; };
|
||
pivot = pivot' 1 { left = []; right = []; };
|
||
in
|
||
if len < 2 then list
|
||
else (sort strictLess pivot.left) ++ [ first ] ++ (sort strictLess pivot.right));
|
||
|
||
|
||
# Return the first (at most) N elements of a list.
|
||
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 =
|
||
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.
|
||
last = list:
|
||
assert list != []; elemAt list (length list - 1);
|
||
|
||
|
||
# Return all elements but the last
|
||
init = list: assert list != []; take (length list - 1) list;
|
||
|
||
|
||
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. O(n^2) complexity.
|
||
unique = list:
|
||
if list == [] then
|
||
[]
|
||
else
|
||
let
|
||
x = head list;
|
||
xs = unique (drop 1 list);
|
||
in [x] ++ remove x xs;
|
||
|
||
|
||
# Intersects list 'e' and another list. O(nm) complexity.
|
||
intersectLists = e: filter (x: elem x e);
|
||
|
||
|
||
# Subtracts list 'e' from another list. O(nm) complexity.
|
||
subtractLists = e: filter (x: !(elem x e));
|
||
|
||
}
|