mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-11-18 07:46:09 +01:00
236 lines
6.5 KiB
Nix
236 lines
6.5 KiB
Nix
# General list operations.
|
|
|
|
with import ./trivial.nix;
|
|
|
|
rec {
|
|
|
|
inherit (builtins) head tail length isList elemAt concatLists filter elem;
|
|
|
|
|
|
# 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);
|
|
|
|
|
|
# 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 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 fold (x: y: (flatten x) ++ 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 = 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 = 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: fold (x: c: 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 = 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 = 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;
|
|
|
|
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 ]) [];
|
|
|
|
|
|
# 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 = 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 = 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);
|
|
|
|
|
|
# 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;
|
|
|
|
|
|
# Zip two lists together.
|
|
zipTwoLists = xs: ys:
|
|
let
|
|
len1 = length xs;
|
|
len2 = length ys;
|
|
len = if len1 < len2 then len1 else len2;
|
|
zipTwoLists' = n:
|
|
if n != len then
|
|
[ { first = elemAt xs n; second = elemAt ys n; } ]
|
|
++ zipTwoLists' (n + 1)
|
|
else [];
|
|
in zipTwoLists' 0;
|
|
|
|
|
|
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
|
|
unique = list:
|
|
if list == [] then
|
|
[]
|
|
else
|
|
let
|
|
x = head list;
|
|
xs = unique (drop 1 list);
|
|
in [x] ++ remove x xs;
|
|
|
|
}
|