forked from mirrors/nixpkgs
afa6c51f27
Nix can perform static scope checking, but whenever code is inside a `with` expression, the analysis breaks down, because it can't know statically what's in the attribute set whose attributes were brought into scope. In those cases, Nix has to assume that everything works out. Except it doesnt. Removing `with` from lib/ revealed an undefined variable in an error message. If that doesn't convince you that we're better off without `with`, I can tell you that this PR results in a 3% evaluation performance improvement because Nix can look up local variables by index. This adds up with applications like the module system. Furthermore, removing `with` makes the binding site of each variable obvious, which helps with comprehension.
676 lines
19 KiB
Nix
676 lines
19 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;
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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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/* Strict version of `foldl`.
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The difference is that evaluation is forced upon access. Usually used
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with small whole results (in contrast with lazily-generated list or large
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lists where only a part is consumed.)
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Type: foldl' :: (b -> a -> b) -> b -> [a] -> b
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*/
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foldl' = builtins.foldl' or foldl;
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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 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 found = filter pred list;
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in if found == [] then default else head found;
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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") flashplayer').
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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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/* 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:
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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 // { ${key} = op (r.${key} or nul) e; }
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) {} lst;
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groupBy = groupBy' (sum: e: sum ++ [e]) [];
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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
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*/
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listDfs = stopOnCycles: before: list:
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let
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dfs' = us: visited: rest:
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let
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c = filter (x: before x us) visited;
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b = partition (x: before x us) rest;
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in if stopOnCycles && (length c > 0)
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then { cycle = us; loops = c; inherit visited rest; }
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else if length b.right == 0
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then # nothing is before us
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{ minimal = us; inherit visited rest; }
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else # grab the first one before us and continue
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dfs' (head b.right)
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([ us ] ++ visited)
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(tail b.right ++ b.wrong);
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in dfs' (head list) [] (tail list);
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/* Sort a list based on a partial ordering using DFS. This
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implementation is O(N^2), if your ordering is linear, use `sort`
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instead.
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`before a b == true` means that `b` should be after `a`
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in the result.
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Example:
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toposort hasPrefix [ "/home/user" "other" "/" "/home" ]
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== { result = [ "/" "/home" "/home/user" "other" ]; }
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toposort hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
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== { cycle = [ "/home/user" "/" "/" ]; # path leading to a cycle
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loops = [ "/" ]; } # loops back to these elements
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toposort hasPrefix [ "other" "/home/user" "/home" "/" ]
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== { result = [ "other" "/" "/home" "/home/user" ]; }
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toposort (a: b: a < b) [ 3 2 1 ] == { result = [ 1 2 3 ]; }
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*/
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toposort = before: list:
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let
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dfsthis = listDfs true before list;
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toporest = toposort before (dfsthis.visited ++ dfsthis.rest);
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in
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if length list < 2
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then # finish
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{ result = list; }
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else if dfsthis ? cycle
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then # there's a cycle, starting from the current vertex, return it
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{ cycle = reverseList ([ dfsthis.cycle ] ++ dfsthis.visited);
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inherit (dfsthis) loops; }
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else if toporest ? cycle
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then # there's a cycle somewhere else in the graph, return it
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toporest
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# Slow, but short. Can be made a bit faster with an explicit stack.
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else # there are no cycles
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{ result = [ dfsthis.minimal ] ++ toporest.result; };
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/* Sort a list based on a comparator function which compares two
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elements and returns true if the first argument is strictly below
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the second argument. The returned list is sorted in an increasing
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order. The implementation does a quick-sort.
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Example:
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sort (a: b: a < b) [ 5 3 7 ]
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=> [ 3 5 7 ]
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*/
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sort = builtins.sort or (
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strictLess: list:
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let
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len = length list;
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first = head list;
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pivot' = n: acc@{ left, right }: let el = elemAt list n; next = pivot' (n + 1); in
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if n == len
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then acc
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else if strictLess first el
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then next { inherit left; right = [ el ] ++ right; }
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else
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next { left = [ el ] ++ left; inherit right; };
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pivot = pivot' 1 { left = []; right = []; };
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in
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if len < 2 then list
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else (sort strictLess pivot.left) ++ [ first ] ++ (sort strictLess pivot.right));
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/* Compare two lists element-by-element.
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Example:
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compareLists compare [] []
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=> 0
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compareLists compare [] [ "a" ]
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=> -1
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compareLists compare [ "a" ] []
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=> 1
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compareLists compare [ "a" "b" ] [ "a" "c" ]
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=> 1
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*/
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compareLists = cmp: a: b:
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if a == []
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then if b == []
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then 0
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else -1
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else if b == []
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then 1
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else let rel = cmp (head a) (head b); in
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if rel == 0
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then compareLists cmp (tail a) (tail b)
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else rel;
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/* Sort list using "Natural sorting".
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Numeric portions of strings are sorted in numeric order.
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Example:
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naturalSort ["disk11" "disk8" "disk100" "disk9"]
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=> ["disk8" "disk9" "disk11" "disk100"]
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naturalSort ["10.46.133.149" "10.5.16.62" "10.54.16.25"]
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=> ["10.5.16.62" "10.46.133.149" "10.54.16.25"]
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naturalSort ["v0.2" "v0.15" "v0.0.9"]
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=> [ "v0.0.9" "v0.2" "v0.15" ]
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*/
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naturalSort = lst:
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let
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vectorise = s: map (x: if isList x then toInt (head x) else x) (builtins.split "(0|[1-9][0-9]*)" s);
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prepared = map (x: [ (vectorise x) x ]) lst; # remember vectorised version for O(n) regex splits
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less = a: b: (compareLists compare (head a) (head b)) < 0;
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in
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map (x: elemAt x 1) (sort less prepared);
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/* Return the first (at most) N elements of a list.
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Type: take :: int -> [a] -> [a]
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Example:
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take 2 [ "a" "b" "c" "d" ]
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=> [ "a" "b" ]
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take 2 [ ]
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=> [ ]
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*/
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take =
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# Number of elements to take
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count: sublist 0 count;
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/* Remove the first (at most) N elements of a list.
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Type: drop :: int -> [a] -> [a]
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Example:
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drop 2 [ "a" "b" "c" "d" ]
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=> [ "c" "d" ]
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drop 2 [ ]
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=> [ ]
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*/
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drop =
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# Number of elements to drop
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count:
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# Input list
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list: sublist count (length list) list;
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/* Return a list consisting of at most `count` elements of `list`,
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starting at index `start`.
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Type: sublist :: int -> int -> [a] -> [a]
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Example:
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sublist 1 3 [ "a" "b" "c" "d" "e" ]
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=> [ "b" "c" "d" ]
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sublist 1 3 [ ]
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=> [ ]
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*/
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sublist =
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# Index at which to start the sublist
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start:
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# Number of elements to take
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count:
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# Input list
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list:
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let len = length list; in
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genList
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(n: elemAt list (n + start))
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(if start >= len then 0
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else if start + count > len then len - start
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else count);
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/* Return the last element of a list.
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This function throws an error if the list is empty.
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Type: last :: [a] -> a
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Example:
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last [ 1 2 3 ]
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=> 3
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*/
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last = list:
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assert lib.assertMsg (list != []) "lists.last: list must not be empty!";
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elemAt list (length list - 1);
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/* Return all elements but the last.
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This function throws an error if the list is empty.
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Type: init :: [a] -> [a]
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Example:
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init [ 1 2 3 ]
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=> [ 1 2 ]
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*/
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init = list:
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assert lib.assertMsg (list != []) "lists.init: list must not be empty!";
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take (length list - 1) list;
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/* Return the image of the cross product of some lists by a function.
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Example:
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crossLists (x:y: "${toString x}${toString y}") [[1 2] [3 4]]
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=> [ "13" "14" "23" "24" ]
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*/
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crossLists = f: foldl (fs: args: concatMap (f: map f args) fs) [f];
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/* Remove duplicate elements from the list. O(n^2) complexity.
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Type: unique :: [a] -> [a]
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Example:
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unique [ 3 2 3 4 ]
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=> [ 3 2 4 ]
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*/
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unique = list:
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if list == [] then
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[]
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else
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let
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x = head list;
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in [x] ++ unique (remove x list);
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/* Intersects list 'e' and another list. O(nm) complexity.
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Example:
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intersectLists [ 1 2 3 ] [ 6 3 2 ]
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=> [ 3 2 ]
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*/
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intersectLists = e: filter (x: elem x e);
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/* Subtracts list 'e' from another list. O(nm) complexity.
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Example:
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subtractLists [ 3 2 ] [ 1 2 3 4 5 3 ]
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|
=> [ 1 4 5 ]
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*/
|
|
subtractLists = e: filter (x: !(elem x e));
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|
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/* Test if two lists have no common element.
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|
It should be slightly more efficient than (intersectLists a b == [])
|
|
*/
|
|
mutuallyExclusive = a: b:
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|
(builtins.length a) == 0 ||
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|
(!(builtins.elem (builtins.head a) b) &&
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mutuallyExclusive (builtins.tail a) b);
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|
}
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