mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-11-22 13:41:26 +00:00
132 lines
3.9 KiB
Nix
132 lines
3.9 KiB
Nix
# General list operations.
|
|
|
|
rec {
|
|
inherit (builtins) head tail isList;
|
|
|
|
|
|
# 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:
|
|
if list == []
|
|
then nul
|
|
else op (head list) (fold op nul (tail list));
|
|
|
|
|
|
# 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:
|
|
if list == []
|
|
then nul
|
|
else foldl op (op nul (head list)) (tail list);
|
|
|
|
|
|
# Concatenate a list of lists.
|
|
concatLists = fold (x: y: x ++ y) [];
|
|
|
|
|
|
# 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];
|
|
|
|
|
|
# Filter a list using a predicate; that is, return a list containing
|
|
# every element from `list' for which `pred' returns true.
|
|
filter = pred: list:
|
|
fold (x: y: if pred x then [x] ++ y else y) [] list;
|
|
|
|
|
|
# Return true if `list' has an element `x':
|
|
elem = x: list: fold (a: bs: x == a || bs) false list;
|
|
|
|
|
|
# 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;
|
|
in if found == [] then default
|
|
else if tail found != [] 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: list:
|
|
if list == [] then false
|
|
else if pred (head list) then true
|
|
else any pred (tail list);
|
|
|
|
|
|
# Return true iff function `pred' returns true for all elements of
|
|
# `list'.
|
|
all = pred: list:
|
|
if list == [] then true
|
|
else if pred (head list) then all pred (tail list)
|
|
else false;
|
|
|
|
|
|
# Return true if each element of a list is equal, false otherwise.
|
|
eqLists = xs: ys:
|
|
if xs == [] && ys == [] then true
|
|
else if xs == [] || ys == [] then false
|
|
else head xs == head ys && eqLists (tail xs) (tail ys);
|
|
|
|
|
|
# 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 builtins.isList x then x else [x];
|
|
|
|
|
|
# Return a list of integers from `first' up to and including `last'.
|
|
range = first: last:
|
|
if builtins.lessThan last first
|
|
then []
|
|
else [first] ++ range (builtins.add 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 = []; };
|
|
|
|
|
|
}
|