8252861507
`pipe` is a useful operator for creating pipelines of functions. It works around the usual problem of e.g. string operations becoming deeply nested functions. In principle, there are four different ways this function could be written: pipe val [ f1 .. fn ] pipe val [ fn .. f1 ] compose [ f1 .. fn ] val compose [ fn .. f1 ] val The third and fourth form mirror composition of functions, they would be the same as e.g. `(f1 << f2 << f3 .. << fn) val`. However, it is not clear which direction the list should have (as one can see in the second form, which is the most absurd. In order not to confuse users, we decide for the most “intuitive” form, which mirrors the way unix pipes work (thus the name `pipe`). The flow of data goes from left to right. Co-Authored-By: Silvan Mosberger <infinisil@icloud.com>
336 lines
8.6 KiB
Nix
336 lines
8.6 KiB
Nix
{ lib }:
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rec {
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## Simple (higher order) functions
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/* The identity function
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For when you need a function that does “nothing”.
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Type: id :: a -> a
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*/
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id =
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# The value to return
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x: x;
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/* The constant function
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Ignores the second argument. If called with only one argument,
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constructs a function that always returns a static value.
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Type: const :: a -> b -> a
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Example:
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let f = const 5; in f 10
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=> 5
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*/
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const =
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# Value to return
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x:
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# Value to ignore
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y: x;
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/* Pipes a value through a list of functions, left to right.
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Type: pipe :: a -> [<functions>] -> <return type of last function>
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Example:
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pipe 2 [
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(x: x + 2) # 2 + 2 = 4
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(x: x * 2) # 4 * 2 = 8
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]
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=> 8
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# ideal to do text transformations
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pipe [ "a/b" "a/c" ] [
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# create the cp command
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(map (file: ''cp "${src}/${file}" $out\n''))
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# concatenate all commands into one string
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lib.concatStrings
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# make that string into a nix derivation
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(pkgs.runCommand "copy-to-out" {})
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]
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=> <drv which copies all files to $out>
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The output type of each function has to be the input type
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of the next function, and the last function returns the
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final value.
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*/
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pipe = val: functions:
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let reverseApply = x: f: f x;
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in builtins.foldl' reverseApply val functions;
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/* note please don’t add a function like `compose = flip pipe`.
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This would confuse users, because the order of the functions
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in the list is not clear. With pipe, it’s obvious that it
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goes first-to-last. With `compose`, not so much.
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*/
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## Named versions corresponding to some builtin operators.
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/* Concatenate two lists
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Type: concat :: [a] -> [a] -> [a]
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Example:
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concat [ 1 2 ] [ 3 4 ]
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=> [ 1 2 3 4 ]
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*/
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concat = x: y: x ++ y;
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/* boolean “or” */
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or = x: y: x || y;
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/* boolean “and” */
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and = x: y: x && y;
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/* bitwise “and” */
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bitAnd = builtins.bitAnd
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or (import ./zip-int-bits.nix
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(a: b: if a==1 && b==1 then 1 else 0));
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/* bitwise “or” */
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bitOr = builtins.bitOr
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or (import ./zip-int-bits.nix
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(a: b: if a==1 || b==1 then 1 else 0));
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/* bitwise “xor” */
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bitXor = builtins.bitXor
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or (import ./zip-int-bits.nix
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(a: b: if a!=b then 1 else 0));
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/* bitwise “not” */
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bitNot = builtins.sub (-1);
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/* Convert a boolean to a string.
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This function uses the strings "true" and "false" to represent
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boolean values. Calling `toString` on a bool instead returns "1"
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and "" (sic!).
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Type: boolToString :: bool -> string
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*/
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boolToString = b: if b then "true" else "false";
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/* Merge two attribute sets shallowly, right side trumps left
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mergeAttrs :: attrs -> attrs -> attrs
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Example:
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mergeAttrs { a = 1; b = 2; } { b = 3; c = 4; }
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=> { a = 1; b = 3; c = 4; }
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*/
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mergeAttrs =
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# Left attribute set
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x:
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# Right attribute set (higher precedence for equal keys)
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y: x // y;
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/* Flip the order of the arguments of a binary function.
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Type: flip :: (a -> b -> c) -> (b -> a -> c)
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Example:
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flip concat [1] [2]
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=> [ 2 1 ]
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*/
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flip = f: a: b: f b a;
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/* Apply function if the supplied argument is non-null.
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Example:
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mapNullable (x: x+1) null
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=> null
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mapNullable (x: x+1) 22
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=> 23
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*/
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mapNullable =
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# Function to call
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f:
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# Argument to check for null before passing it to `f`
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a: if a == null then a else f a;
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# Pull in some builtins not included elsewhere.
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inherit (builtins)
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pathExists readFile isBool
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isInt isFloat add sub lessThan
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seq deepSeq genericClosure;
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## nixpks version strings
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/* Returns the current full nixpkgs version number. */
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version = release + versionSuffix;
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/* Returns the current nixpkgs release number as string. */
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release = lib.strings.fileContents ../.version;
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/* Returns the current nixpkgs release code name.
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On each release the first letter is bumped and a new animal is chosen
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starting with that new letter.
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*/
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codeName = "Markhor";
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/* Returns the current nixpkgs version suffix as string. */
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versionSuffix =
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let suffixFile = ../.version-suffix;
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in if pathExists suffixFile
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then lib.strings.fileContents suffixFile
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else "pre-git";
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/* Attempts to return the the current revision of nixpkgs and
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returns the supplied default value otherwise.
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Type: revisionWithDefault :: string -> string
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*/
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revisionWithDefault =
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# Default value to return if revision can not be determined
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default:
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let
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revisionFile = "${toString ./..}/.git-revision";
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gitRepo = "${toString ./..}/.git";
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in if lib.pathIsDirectory gitRepo
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then lib.commitIdFromGitRepo gitRepo
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else if lib.pathExists revisionFile then lib.fileContents revisionFile
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else default;
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nixpkgsVersion = builtins.trace "`lib.nixpkgsVersion` is deprecated, use `lib.version` instead!" version;
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/* Determine whether the function is being called from inside a Nix
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shell.
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Type: inNixShell :: bool
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*/
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inNixShell = builtins.getEnv "IN_NIX_SHELL" != "";
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## Integer operations
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/* Return minimum of two numbers. */
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min = x: y: if x < y then x else y;
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/* Return maximum of two numbers. */
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max = x: y: if x > y then x else y;
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/* Integer modulus
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Example:
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mod 11 10
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=> 1
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mod 1 10
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=> 1
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*/
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mod = base: int: base - (int * (builtins.div base int));
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## Comparisons
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/* C-style comparisons
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a < b, compare a b => -1
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a == b, compare a b => 0
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a > b, compare a b => 1
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*/
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compare = a: b:
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if a < b
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then -1
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else if a > b
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then 1
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else 0;
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/* Split type into two subtypes by predicate `p`, take all elements
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of the first subtype to be less than all the elements of the
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second subtype, compare elements of a single subtype with `yes`
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and `no` respectively.
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Type: (a -> bool) -> (a -> a -> int) -> (a -> a -> int) -> (a -> a -> int)
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Example:
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let cmp = splitByAndCompare (hasPrefix "foo") compare compare; in
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cmp "a" "z" => -1
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cmp "fooa" "fooz" => -1
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cmp "f" "a" => 1
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cmp "fooa" "a" => -1
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# while
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compare "fooa" "a" => 1
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*/
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splitByAndCompare =
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# Predicate
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p:
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# Comparison function if predicate holds for both values
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yes:
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# Comparison function if predicate holds for neither value
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no:
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# First value to compare
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a:
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# Second value to compare
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b:
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if p a
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then if p b then yes a b else -1
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else if p b then 1 else no a b;
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/* Reads a JSON file.
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Type :: path -> any
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*/
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importJSON = path:
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builtins.fromJSON (builtins.readFile path);
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## Warnings
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# See https://github.com/NixOS/nix/issues/749. Eventually we'd like these
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# to expand to Nix builtins that carry metadata so that Nix can filter out
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# the INFO messages without parsing the message string.
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#
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# Usage:
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# {
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# foo = lib.warn "foo is deprecated" oldFoo;
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# }
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#
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# TODO: figure out a clever way to integrate location information from
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# something like __unsafeGetAttrPos.
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warn = msg: builtins.trace "[1;31mwarning: ${msg}[0m";
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info = msg: builtins.trace "INFO: ${msg}";
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showWarnings = warnings: res: lib.fold (w: x: warn w x) res warnings;
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## Function annotations
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/* Add metadata about expected function arguments to a function.
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The metadata should match the format given by
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builtins.functionArgs, i.e. a set from expected argument to a bool
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representing whether that argument has a default or not.
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setFunctionArgs : (a → b) → Map String Bool → (a → b)
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This function is necessary because you can't dynamically create a
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function of the { a, b ? foo, ... }: format, but some facilities
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like callPackage expect to be able to query expected arguments.
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*/
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setFunctionArgs = f: args:
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{ # TODO: Should we add call-time "type" checking like built in?
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__functor = self: f;
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__functionArgs = args;
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};
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/* Extract the expected function arguments from a function.
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This works both with nix-native { a, b ? foo, ... }: style
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functions and functions with args set with 'setFunctionArgs'. It
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has the same return type and semantics as builtins.functionArgs.
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setFunctionArgs : (a → b) → Map String Bool.
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*/
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functionArgs = f: f.__functionArgs or (builtins.functionArgs f);
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/* Check whether something is a function or something
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annotated with function args.
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*/
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isFunction = f: builtins.isFunction f ||
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(f ? __functor && isFunction (f.__functor f));
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}
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