mirror of
https://github.com/NixOS/nixpkgs.git
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c2a744b9af
Expands on some of the function comments and add some of the special syntaxes recognised by nixdoc.
291 lines
7.2 KiB
Nix
291 lines
7.2 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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## 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 isNull a 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 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 "WARNING: ${msg}";
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info = msg: builtins.trace "INFO: ${msg}";
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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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