d33127863e
The deprecation warnings in lib were wildly inconsistent. Different formulations were used in different places for the same meaning. Some warnings used builtins.trace instead of lib.warn, which prevents silencing; one even only had a comment instead. Make everything more uniform.
900 lines
26 KiB
Nix
900 lines
26 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 warn;
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inherit (lib.attrsets) mapAttrs;
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inherit (lib.lists) sort;
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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)
|
|
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.
|
|
|
|
See also [`sortOn`](#function-library-lib.lists.sortOn), which applies the
|
|
default comparison on a function-derived property, and may be more efficient.
|
|
|
|
Example:
|
|
sort (p: q: p < q) [ 5 3 7 ]
|
|
=> [ 3 5 7 ]
|
|
|
|
Type:
|
|
sort :: (a -> a -> Bool) -> [a] -> [a]
|
|
*/
|
|
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));
|
|
|
|
/*
|
|
Sort a list based on the default comparison of a derived property `b`.
|
|
|
|
The items are returned in `b`-increasing order.
|
|
|
|
**Performance**:
|
|
|
|
The passed function `f` is only evaluated once per item,
|
|
unlike an unprepared [`sort`](#function-library-lib.lists.sort) using
|
|
`f p < f q`.
|
|
|
|
**Laws**:
|
|
```nix
|
|
sortOn f == sort (p: q: f p < f q)
|
|
```
|
|
|
|
Example:
|
|
sortOn stringLength [ "aa" "b" "cccc" ]
|
|
=> [ "b" "aa" "cccc" ]
|
|
|
|
Type:
|
|
sortOn :: (a -> b) -> [a] -> [a], for comparable b
|
|
*/
|
|
sortOn = f: list:
|
|
let
|
|
# Heterogenous list as pair may be ugly, but requires minimal allocations.
|
|
pairs = map (x: [(f x) x]) list;
|
|
in
|
|
map
|
|
(x: builtins.elemAt x 1)
|
|
(sort
|
|
# Compare the first element of the pairs
|
|
# Do not factor out the `<`, to avoid calls in hot code; duplicate instead.
|
|
(a: b: head a < head b)
|
|
pairs);
|
|
|
|
/* 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 = warn
|
|
"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 ]) [];
|
|
|
|
/* Check if list contains only unique elements. O(n^2) complexity.
|
|
|
|
Type: allUnique :: [a] -> bool
|
|
|
|
Example:
|
|
allUnique [ 3 2 3 4 ]
|
|
=> false
|
|
allUnique [ 3 2 4 1 ]
|
|
=> true
|
|
*/
|
|
allUnique = list: (length (unique list) == length list);
|
|
|
|
|
|
/* 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);
|
|
|
|
}
|