3b6169f87b
To maintain backwards compatibility, this can't be changed in the Nix language. We can however ensure that the version Nixpkgs has the more intuitive behavior.
845 lines
24 KiB
Nix
845 lines
24 KiB
Nix
# General list operations.
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{ lib }:
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let
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inherit (lib.strings) toInt;
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inherit (lib.trivial) compare min id;
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inherit (lib.attrsets) mapAttrs;
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in
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rec {
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inherit (builtins) head tail length isList elemAt concatLists filter elem genList map;
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/* Create a list consisting of a single element. `singleton x` is
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sometimes more convenient with respect to indentation than `[x]`
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when x spans multiple lines.
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Type: singleton :: a -> [a]
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Example:
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singleton "foo"
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=> [ "foo" ]
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*/
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singleton = x: [x];
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/* Apply the function to each element in the list. Same as `map`, but arguments
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flipped.
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Type: forEach :: [a] -> (a -> b) -> [b]
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Example:
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forEach [ 1 2 ] (x:
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toString x
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)
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=> [ "1" "2" ]
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*/
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forEach = xs: f: map f xs;
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/* “right fold” a binary function `op` between successive elements of
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`list` with `nul` as the starting value, i.e.,
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`foldr op nul [x_1 x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))`.
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Type: foldr :: (a -> b -> b) -> b -> [a] -> b
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Example:
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concat = foldr (a: b: a + b) "z"
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concat [ "a" "b" "c" ]
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=> "abcz"
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# different types
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strange = foldr (int: str: toString (int + 1) + str) "a"
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strange [ 1 2 3 4 ]
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=> "2345a"
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*/
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foldr = op: nul: list:
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let
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len = length list;
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fold' = n:
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if n == len
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then nul
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else op (elemAt list n) (fold' (n + 1));
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in fold' 0;
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/* `fold` is an alias of `foldr` for historic reasons */
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# FIXME(Profpatsch): deprecate?
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fold = foldr;
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/* “left fold”, like `foldr`, but from the left:
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`foldl op nul [x_1 x_2 ... x_n] == op (... (op (op nul x_1) x_2) ... x_n)`.
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Type: foldl :: (b -> a -> b) -> b -> [a] -> b
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Example:
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lconcat = foldl (a: b: a + b) "z"
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lconcat [ "a" "b" "c" ]
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=> "zabc"
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# different types
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lstrange = foldl (str: int: str + toString (int + 1)) "a"
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lstrange [ 1 2 3 4 ]
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=> "a2345"
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*/
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foldl = op: nul: list:
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let
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foldl' = n:
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if n == -1
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then nul
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else op (foldl' (n - 1)) (elemAt list n);
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in foldl' (length list - 1);
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/*
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Reduce a list by applying a binary operator from left to right,
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starting with an initial accumulator.
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Before each application of the operator, the accumulator value is evaluated.
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This behavior makes this function stricter than [`foldl`](#function-library-lib.lists.foldl).
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Unlike [`builtins.foldl'`](https://nixos.org/manual/nix/unstable/language/builtins.html#builtins-foldl'),
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the initial accumulator argument is evaluated before the first iteration.
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A call like
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```nix
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foldl' op acc₀ [ x₀ x₁ x₂ ... xₙ₋₁ xₙ ]
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```
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is (denotationally) equivalent to the following,
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but with the added benefit that `foldl'` itself will never overflow the stack.
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```nix
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let
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acc₁ = builtins.seq acc₀ (op acc₀ x₀ );
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acc₂ = builtins.seq acc₁ (op acc₁ x₁ );
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acc₃ = builtins.seq acc₂ (op acc₂ x₂ );
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...
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accₙ = builtins.seq accₙ₋₁ (op accₙ₋₁ xₙ₋₁);
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accₙ₊₁ = builtins.seq accₙ (op accₙ xₙ );
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in
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accₙ₊₁
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# Or ignoring builtins.seq
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op (op (... (op (op (op acc₀ x₀) x₁) x₂) ...) xₙ₋₁) xₙ
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```
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Type: foldl' :: (acc -> x -> acc) -> acc -> [x] -> acc
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Example:
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foldl' (acc: x: acc + x) 0 [1 2 3]
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=> 6
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*/
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foldl' =
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/* The binary operation to run, where the two arguments are:
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1. `acc`: The current accumulator value: Either the initial one for the first iteration, or the result of the previous iteration
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2. `x`: The corresponding list element for this iteration
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*/
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op:
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# The initial accumulator value
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acc:
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# The list to fold
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list:
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# The builtin `foldl'` is a bit lazier than one might expect.
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# See https://github.com/NixOS/nix/pull/7158.
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# In particular, the initial accumulator value is not forced before the first iteration starts.
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builtins.seq acc
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(builtins.foldl' op acc list);
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/* Map with index starting from 0
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Type: imap0 :: (int -> a -> b) -> [a] -> [b]
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Example:
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imap0 (i: v: "${v}-${toString i}") ["a" "b"]
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=> [ "a-0" "b-1" ]
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*/
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imap0 = f: list: genList (n: f n (elemAt list n)) (length list);
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/* Map with index starting from 1
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Type: imap1 :: (int -> a -> b) -> [a] -> [b]
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Example:
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imap1 (i: v: "${v}-${toString i}") ["a" "b"]
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=> [ "a-1" "b-2" ]
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*/
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imap1 = f: list: genList (n: f (n + 1) (elemAt list n)) (length list);
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/* Map and concatenate the result.
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Type: concatMap :: (a -> [b]) -> [a] -> [b]
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Example:
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concatMap (x: [x] ++ ["z"]) ["a" "b"]
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=> [ "a" "z" "b" "z" ]
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*/
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concatMap = builtins.concatMap or (f: list: concatLists (map f list));
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/* Flatten the argument into a single list; that is, nested lists are
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spliced into the top-level lists.
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Example:
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flatten [1 [2 [3] 4] 5]
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=> [1 2 3 4 5]
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flatten 1
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=> [1]
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*/
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flatten = x:
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if isList x
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then concatMap (y: flatten y) x
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else [x];
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/* Remove elements equal to 'e' from a list. Useful for buildInputs.
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Type: remove :: a -> [a] -> [a]
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Example:
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remove 3 [ 1 3 4 3 ]
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=> [ 1 4 ]
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*/
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remove =
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# Element to remove from the list
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e: filter (x: x != e);
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/* Find the sole element in the list matching the specified
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predicate, returns `default` if no such element exists, or
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`multiple` if there are multiple matching elements.
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Type: findSingle :: (a -> bool) -> a -> a -> [a] -> a
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Example:
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findSingle (x: x == 3) "none" "multiple" [ 1 3 3 ]
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=> "multiple"
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findSingle (x: x == 3) "none" "multiple" [ 1 3 ]
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=> 3
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findSingle (x: x == 3) "none" "multiple" [ 1 9 ]
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=> "none"
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*/
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findSingle =
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# Predicate
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pred:
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# Default value to return if element was not found.
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default:
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# Default value to return if more than one element was found
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multiple:
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# Input list
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list:
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let found = filter pred list; len = length found;
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in if len == 0 then default
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else if len != 1 then multiple
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else head found;
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/* Find the first index in the list matching the specified
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predicate or return `default` if no such element exists.
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Type: findFirstIndex :: (a -> Bool) -> b -> [a] -> (Int | b)
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Example:
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findFirstIndex (x: x > 3) null [ 0 6 4 ]
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=> 1
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findFirstIndex (x: x > 9) null [ 0 6 4 ]
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=> null
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*/
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findFirstIndex =
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# Predicate
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pred:
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# Default value to return
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default:
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# Input list
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list:
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let
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# A naive recursive implementation would be much simpler, but
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# would also overflow the evaluator stack. We use `foldl'` as a workaround
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# because it reuses the same stack space, evaluating the function for one
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# element after another. We can't return early, so this means that we
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# sacrifice early cutoff, but that appears to be an acceptable cost. A
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# clever scheme with "exponential search" is possible, but appears over-
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# engineered for now. See https://github.com/NixOS/nixpkgs/pull/235267
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# Invariant:
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# - if index < 0 then el == elemAt list (- index - 1) and all elements before el didn't satisfy pred
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# - if index >= 0 then pred (elemAt list index) and all elements before (elemAt list index) didn't satisfy pred
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#
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# We start with index -1 and the 0'th element of the list, which satisfies the invariant
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resultIndex = foldl' (index: el:
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if index < 0 then
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# No match yet before the current index, we need to check the element
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if pred el then
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# We have a match! Turn it into the actual index to prevent future iterations from modifying it
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- index - 1
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else
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# Still no match, update the index to the next element (we're counting down, so minus one)
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index - 1
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else
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# There's already a match, propagate the index without evaluating anything
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index
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) (-1) list;
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in
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if resultIndex < 0 then
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default
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else
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resultIndex;
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/* Find the first element in the list matching the specified
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predicate or return `default` if no such element exists.
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Type: findFirst :: (a -> bool) -> a -> [a] -> a
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Example:
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findFirst (x: x > 3) 7 [ 1 6 4 ]
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=> 6
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findFirst (x: x > 9) 7 [ 1 6 4 ]
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=> 7
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*/
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findFirst =
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# Predicate
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pred:
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# Default value to return
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default:
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# Input list
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list:
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let
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index = findFirstIndex pred null list;
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in
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if index == null then
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default
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else
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elemAt list index;
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/* Return true if function `pred` returns true for at least one
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element of `list`.
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Type: any :: (a -> bool) -> [a] -> bool
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Example:
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any isString [ 1 "a" { } ]
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=> true
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any isString [ 1 { } ]
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=> false
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*/
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any = builtins.any or (pred: foldr (x: y: if pred x then true else y) false);
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/* Return true if function `pred` returns true for all elements of
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`list`.
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Type: all :: (a -> bool) -> [a] -> bool
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Example:
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all (x: x < 3) [ 1 2 ]
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=> true
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all (x: x < 3) [ 1 2 3 ]
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=> false
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*/
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all = builtins.all or (pred: foldr (x: y: if pred x then y else false) true);
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/* Count how many elements of `list` match the supplied predicate
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function.
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Type: count :: (a -> bool) -> [a] -> int
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Example:
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count (x: x == 3) [ 3 2 3 4 6 ]
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=> 2
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*/
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count =
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# Predicate
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pred: foldl' (c: x: if pred x then c + 1 else c) 0;
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/* Return a singleton list or an empty list, depending on a boolean
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value. Useful when building lists with optional elements
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(e.g. `++ optional (system == "i686-linux") firefox`).
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Type: optional :: bool -> a -> [a]
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Example:
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optional true "foo"
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=> [ "foo" ]
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optional false "foo"
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=> [ ]
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*/
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optional = cond: elem: if cond then [elem] else [];
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/* Return a list or an empty list, depending on a boolean value.
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Type: optionals :: bool -> [a] -> [a]
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Example:
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optionals true [ 2 3 ]
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=> [ 2 3 ]
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optionals false [ 2 3 ]
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=> [ ]
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*/
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optionals =
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# Condition
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cond:
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# List to return if condition is true
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elems: if cond then elems else [];
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/* If argument is a list, return it; else, wrap it in a singleton
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list. If you're using this, you should almost certainly
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reconsider if there isn't a more "well-typed" approach.
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Example:
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toList [ 1 2 ]
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=> [ 1 2 ]
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toList "hi"
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=> [ "hi "]
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*/
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toList = x: if isList x then x else [x];
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/* Return a list of integers from `first` up to and including `last`.
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Type: range :: int -> int -> [int]
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Example:
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range 2 4
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=> [ 2 3 4 ]
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range 3 2
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=> [ ]
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*/
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range =
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# First integer in the range
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first:
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# Last integer in the range
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last:
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if first > last then
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[]
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else
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genList (n: first + n) (last - first + 1);
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/* Return a list with `n` copies of an element.
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Type: replicate :: int -> a -> [a]
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Example:
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replicate 3 "a"
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=> [ "a" "a" "a" ]
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replicate 2 true
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=> [ true true ]
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*/
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replicate = n: elem: genList (_: elem) n;
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/* Splits the elements of a list in two lists, `right` and
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`wrong`, depending on the evaluation of a predicate.
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Type: (a -> bool) -> [a] -> { right :: [a]; wrong :: [a]; }
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Example:
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partition (x: x > 2) [ 5 1 2 3 4 ]
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=> { right = [ 5 3 4 ]; wrong = [ 1 2 ]; }
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*/
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partition = builtins.partition or (pred:
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foldr (h: t:
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if pred h
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then { right = [h] ++ t.right; wrong = t.wrong; }
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else { right = t.right; wrong = [h] ++ t.wrong; }
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) { right = []; wrong = []; });
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/* Splits the elements of a list into many lists, using the return value of a predicate.
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Predicate should return a string which becomes keys of attrset `groupBy` returns.
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`groupBy'` allows to customise the combining function and initial value
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Example:
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groupBy (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
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=> { true = [ 5 3 4 ]; false = [ 1 2 ]; }
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groupBy (x: x.name) [ {name = "icewm"; script = "icewm &";}
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{name = "xfce"; script = "xfce4-session &";}
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{name = "icewm"; script = "icewmbg &";}
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{name = "mate"; script = "gnome-session &";}
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]
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=> { icewm = [ { name = "icewm"; script = "icewm &"; }
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{ name = "icewm"; script = "icewmbg &"; } ];
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mate = [ { name = "mate"; script = "gnome-session &"; } ];
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xfce = [ { name = "xfce"; script = "xfce4-session &"; } ];
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}
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groupBy' builtins.add 0 (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
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=> { true = 12; false = 3; }
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*/
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groupBy' = op: nul: pred: lst: mapAttrs (name: foldl op nul) (groupBy pred lst);
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groupBy = builtins.groupBy or (
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pred: foldl' (r: e:
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let
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key = pred e;
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in
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r // { ${key} = (r.${key} or []) ++ [e]; }
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) {});
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/* Merges two lists of the same size together. If the sizes aren't the same
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the merging stops at the shortest. How both lists are merged is defined
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by the first argument.
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Type: zipListsWith :: (a -> b -> c) -> [a] -> [b] -> [c]
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Example:
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zipListsWith (a: b: a + b) ["h" "l"] ["e" "o"]
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=> ["he" "lo"]
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*/
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zipListsWith =
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# Function to zip elements of both lists
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f:
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# First list
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fst:
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# Second list
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snd:
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genList
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(n: f (elemAt fst n) (elemAt snd n)) (min (length fst) (length snd));
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/* Merges two lists of the same size together. If the sizes aren't the same
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the merging stops at the shortest.
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Type: zipLists :: [a] -> [b] -> [{ fst :: a; snd :: b; }]
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Example:
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zipLists [ 1 2 ] [ "a" "b" ]
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=> [ { fst = 1; snd = "a"; } { fst = 2; snd = "b"; } ]
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*/
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zipLists = zipListsWith (fst: snd: { inherit fst snd; });
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/* Reverse the order of the elements of a list.
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Type: reverseList :: [a] -> [a]
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Example:
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reverseList [ "b" "o" "j" ]
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=> [ "j" "o" "b" ]
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*/
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reverseList = xs:
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let l = length xs; in genList (n: elemAt xs (l - n - 1)) l;
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/* Depth-First Search (DFS) for lists `list != []`.
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`before a b == true` means that `b` depends on `a` (there's an
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edge from `b` to `a`).
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Example:
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listDfs true hasPrefix [ "/home/user" "other" "/" "/home" ]
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== { minimal = "/"; # minimal element
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visited = [ "/home/user" ]; # seen elements (in reverse order)
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rest = [ "/home" "other" ]; # everything else
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}
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listDfs true hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
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== { cycle = "/"; # cycle encountered at this element
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loops = [ "/" ]; # and continues to these elements
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visited = [ "/" "/home/user" ]; # elements leading to the cycle (in reverse order)
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rest = [ "/home" "other" ]; # everything else
|
|
|
|
*/
|
|
listDfs = stopOnCycles: before: list:
|
|
let
|
|
dfs' = us: visited: rest:
|
|
let
|
|
c = filter (x: before x us) visited;
|
|
b = partition (x: before x us) rest;
|
|
in if stopOnCycles && (length c > 0)
|
|
then { cycle = us; loops = c; inherit visited rest; }
|
|
else if length b.right == 0
|
|
then # nothing is before us
|
|
{ minimal = us; inherit visited rest; }
|
|
else # grab the first one before us and continue
|
|
dfs' (head b.right)
|
|
([ us ] ++ visited)
|
|
(tail b.right ++ b.wrong);
|
|
in dfs' (head list) [] (tail list);
|
|
|
|
/* Sort a list based on a partial ordering using DFS. This
|
|
implementation is O(N^2), if your ordering is linear, use `sort`
|
|
instead.
|
|
|
|
`before a b == true` means that `b` should be after `a`
|
|
in the result.
|
|
|
|
Example:
|
|
|
|
toposort hasPrefix [ "/home/user" "other" "/" "/home" ]
|
|
== { result = [ "/" "/home" "/home/user" "other" ]; }
|
|
|
|
toposort hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
|
|
== { cycle = [ "/home/user" "/" "/" ]; # path leading to a cycle
|
|
loops = [ "/" ]; } # loops back to these elements
|
|
|
|
toposort hasPrefix [ "other" "/home/user" "/home" "/" ]
|
|
== { result = [ "other" "/" "/home" "/home/user" ]; }
|
|
|
|
toposort (a: b: a < b) [ 3 2 1 ] == { result = [ 1 2 3 ]; }
|
|
|
|
*/
|
|
toposort = before: list:
|
|
let
|
|
dfsthis = listDfs true before list;
|
|
toporest = toposort before (dfsthis.visited ++ dfsthis.rest);
|
|
in
|
|
if length list < 2
|
|
then # finish
|
|
{ result = list; }
|
|
else if dfsthis ? cycle
|
|
then # there's a cycle, starting from the current vertex, return it
|
|
{ cycle = reverseList ([ dfsthis.cycle ] ++ dfsthis.visited);
|
|
inherit (dfsthis) loops; }
|
|
else if toporest ? cycle
|
|
then # there's a cycle somewhere else in the graph, return it
|
|
toporest
|
|
# Slow, but short. Can be made a bit faster with an explicit stack.
|
|
else # there are no cycles
|
|
{ result = [ dfsthis.minimal ] ++ toporest.result; };
|
|
|
|
/* 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.
|
|
|
|
Example:
|
|
sort (a: b: a < b) [ 5 3 7 ]
|
|
=> [ 3 5 7 ]
|
|
*/
|
|
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));
|
|
|
|
/* 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;
|
|
|
|
/* Sort list using "Natural sorting".
|
|
Numeric portions of strings are sorted in numeric order.
|
|
|
|
Example:
|
|
naturalSort ["disk11" "disk8" "disk100" "disk9"]
|
|
=> ["disk8" "disk9" "disk11" "disk100"]
|
|
naturalSort ["10.46.133.149" "10.5.16.62" "10.54.16.25"]
|
|
=> ["10.5.16.62" "10.46.133.149" "10.54.16.25"]
|
|
naturalSort ["v0.2" "v0.15" "v0.0.9"]
|
|
=> [ "v0.0.9" "v0.2" "v0.15" ]
|
|
*/
|
|
naturalSort = lst:
|
|
let
|
|
vectorise = s: map (x: if isList x then toInt (head x) else x) (builtins.split "(0|[1-9][0-9]*)" s);
|
|
prepared = map (x: [ (vectorise x) x ]) lst; # remember vectorised version for O(n) regex splits
|
|
less = a: b: (compareLists compare (head a) (head b)) < 0;
|
|
in
|
|
map (x: elemAt x 1) (sort less prepared);
|
|
|
|
/* Return the first (at most) N elements of a list.
|
|
|
|
Type: take :: int -> [a] -> [a]
|
|
|
|
Example:
|
|
take 2 [ "a" "b" "c" "d" ]
|
|
=> [ "a" "b" ]
|
|
take 2 [ ]
|
|
=> [ ]
|
|
*/
|
|
take =
|
|
# Number of elements to take
|
|
count: sublist 0 count;
|
|
|
|
/* Remove the first (at most) N elements of a list.
|
|
|
|
Type: drop :: int -> [a] -> [a]
|
|
|
|
Example:
|
|
drop 2 [ "a" "b" "c" "d" ]
|
|
=> [ "c" "d" ]
|
|
drop 2 [ ]
|
|
=> [ ]
|
|
*/
|
|
drop =
|
|
# Number of elements to drop
|
|
count:
|
|
# Input list
|
|
list: sublist count (length list) list;
|
|
|
|
/* Whether the first list is a prefix of the second list.
|
|
|
|
Type: hasPrefix :: [a] -> [a] -> bool
|
|
|
|
Example:
|
|
hasPrefix [ 1 2 ] [ 1 2 3 4 ]
|
|
=> true
|
|
hasPrefix [ 0 1 ] [ 1 2 3 4 ]
|
|
=> false
|
|
*/
|
|
hasPrefix =
|
|
list1:
|
|
list2:
|
|
take (length list1) list2 == list1;
|
|
|
|
/* Remove the first list as a prefix from the second list.
|
|
Error if the first list isn't a prefix of the second list.
|
|
|
|
Type: removePrefix :: [a] -> [a] -> [a]
|
|
|
|
Example:
|
|
removePrefix [ 1 2 ] [ 1 2 3 4 ]
|
|
=> [ 3 4 ]
|
|
removePrefix [ 0 1 ] [ 1 2 3 4 ]
|
|
=> <error>
|
|
*/
|
|
removePrefix =
|
|
list1:
|
|
list2:
|
|
if hasPrefix list1 list2 then
|
|
drop (length list1) list2
|
|
else
|
|
throw "lib.lists.removePrefix: First argument is not a list prefix of the second argument";
|
|
|
|
/* Return a list consisting of at most `count` elements of `list`,
|
|
starting at index `start`.
|
|
|
|
Type: sublist :: int -> int -> [a] -> [a]
|
|
|
|
Example:
|
|
sublist 1 3 [ "a" "b" "c" "d" "e" ]
|
|
=> [ "b" "c" "d" ]
|
|
sublist 1 3 [ ]
|
|
=> [ ]
|
|
*/
|
|
sublist =
|
|
# Index at which to start the sublist
|
|
start:
|
|
# Number of elements to take
|
|
count:
|
|
# Input list
|
|
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);
|
|
|
|
/* The common prefix of two lists.
|
|
|
|
Type: commonPrefix :: [a] -> [a] -> [a]
|
|
|
|
Example:
|
|
commonPrefix [ 1 2 3 4 5 6 ] [ 1 2 4 8 ]
|
|
=> [ 1 2 ]
|
|
commonPrefix [ 1 2 3 ] [ 1 2 3 4 5 ]
|
|
=> [ 1 2 3 ]
|
|
commonPrefix [ 1 2 3 ] [ 4 5 6 ]
|
|
=> [ ]
|
|
*/
|
|
commonPrefix =
|
|
list1:
|
|
list2:
|
|
let
|
|
# Zip the lists together into a list of booleans whether each element matches
|
|
matchings = zipListsWith (fst: snd: fst != snd) list1 list2;
|
|
# Find the first index where the elements don't match,
|
|
# which will then also be the length of the common prefix.
|
|
# If all elements match, we fall back to the length of the zipped list,
|
|
# which is the same as the length of the smaller list.
|
|
commonPrefixLength = findFirstIndex id (length matchings) matchings;
|
|
in
|
|
take commonPrefixLength list1;
|
|
|
|
/* Return the last element of a list.
|
|
|
|
This function throws an error if the list is empty.
|
|
|
|
Type: last :: [a] -> a
|
|
|
|
Example:
|
|
last [ 1 2 3 ]
|
|
=> 3
|
|
*/
|
|
last = list:
|
|
assert lib.assertMsg (list != []) "lists.last: list must not be empty!";
|
|
elemAt list (length list - 1);
|
|
|
|
/* Return all elements but the last.
|
|
|
|
This function throws an error if the list is empty.
|
|
|
|
Type: init :: [a] -> [a]
|
|
|
|
Example:
|
|
init [ 1 2 3 ]
|
|
=> [ 1 2 ]
|
|
*/
|
|
init = list:
|
|
assert lib.assertMsg (list != []) "lists.init: list must not be empty!";
|
|
take (length list - 1) list;
|
|
|
|
|
|
/* Return the image of the cross product of some lists by a function.
|
|
|
|
Example:
|
|
crossLists (x:y: "${toString x}${toString y}") [[1 2] [3 4]]
|
|
=> [ "13" "14" "23" "24" ]
|
|
*/
|
|
crossLists = builtins.trace
|
|
"lib.crossLists is deprecated, use lib.cartesianProductOfSets instead"
|
|
(f: foldl (fs: args: concatMap (f: map f args) fs) [f]);
|
|
|
|
|
|
/* Remove duplicate elements from the list. O(n^2) complexity.
|
|
|
|
Type: unique :: [a] -> [a]
|
|
|
|
Example:
|
|
unique [ 3 2 3 4 ]
|
|
=> [ 3 2 4 ]
|
|
*/
|
|
unique = foldl' (acc: e: if elem e acc then acc else acc ++ [ e ]) [];
|
|
|
|
/* Intersects list 'e' and another list. O(nm) complexity.
|
|
|
|
Example:
|
|
intersectLists [ 1 2 3 ] [ 6 3 2 ]
|
|
=> [ 3 2 ]
|
|
*/
|
|
intersectLists = e: filter (x: elem x e);
|
|
|
|
/* Subtracts list 'e' from another list. O(nm) complexity.
|
|
|
|
Example:
|
|
subtractLists [ 3 2 ] [ 1 2 3 4 5 3 ]
|
|
=> [ 1 4 5 ]
|
|
*/
|
|
subtractLists = e: filter (x: !(elem x e));
|
|
|
|
/* Test if two lists have no common element.
|
|
It should be slightly more efficient than (intersectLists a b == [])
|
|
*/
|
|
mutuallyExclusive = a: b: length a == 0 || !(any (x: elem x a) b);
|
|
|
|
}
|