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{ lib }:
rec {
## Simple (higher order) functions
/* The identity function
For when you need a function that does “nothing”.
Type: id :: a -> a
*/
id = x: x;
/* The constant function
Ignores the second argument.
Or: Construct a function that always returns a static value.
Type: const :: a -> b -> a
Example:
let f = const 5; in f 10
=> 5
*/
const = x: y: x;
## Named versions corresponding to some builtin operators.
/* Concatenate two lists */
concat = x: y: x ++ y;
/* boolean “or” */
or = x: y: x || y;
/* boolean “and” */
and = x: y: x && y;
/* bitwise “and” */
bitAnd = builtins.bitAnd
or import ./zip-int-bits.nix
(a: b: if a==1 && b==1 then 1 else 0);
/* bitwise “or” */
bitOr = builtins.bitOr
or import ./zip-int-bits.nix
(a: b: if a==1 || b==1 then 1 else 0);
/* bitwise “xor” */
bitXor = builtins.bitXor
or import ./zip-int-bits.nix
(a: b: if a!=b then 1 else 0);
/* bitwise “not” */
bitNot = builtins.sub (-1);
/* Convert a boolean to a string.
Note that toString on a bool returns "1" and "".
*/
boolToString = b: if b then "true" else "false";
/* Merge two attribute sets shallowly, right side trumps left
Example:
mergeAttrs { a = 1; b = 2; } { b = 3; c = 4; }
=> { a = 1; b = 3; c = 4; }
*/
mergeAttrs = x: y: x // y;
/* Flip the order of the arguments of a binary function.
Example:
flip concat [1] [2]
=> [ 2 1 ]
*/
flip = f: a: b: f b a;
/* Apply function if argument is non-null.
Example:
mapNullable (x: x+1) null
=> null
mapNullable (x: x+1) 22
=> 23
*/
mapNullable = f: a: if isNull a then a else f a;
# Pull in some builtins not included elsewhere.
inherit (builtins)
pathExists readFile isBool
isInt isFloat add sub lessThan
seq deepSeq genericClosure;
## nixpks version strings
# The current full nixpkgs version number.
version = release + versionSuffix;
# The current nixpkgs version number as string.
release = lib.strings.fileContents ../.version;
# The current nixpkgs version suffix as string.
versionSuffix =
let suffixFile = ../.version-suffix;
in if pathExists suffixFile
then lib.strings.fileContents suffixFile
else "pre-git";
nixpkgsVersion = builtins.trace "`lib.nixpkgsVersion` is deprecated, use `lib.version` instead!" version;
# Whether we're being called by nix-shell.
inNixShell = builtins.getEnv "IN_NIX_SHELL" != "";
## Integer operations
# Return minimum/maximum of two numbers.
min = x: y: if x < y then x else y;
max = x: y: if x > y then x else y;
/* Integer modulus
Example:
mod 11 10
=> 1
mod 1 10
=> 1
*/
mod = base: int: base - (int * (builtins.div base int));
## Comparisons
/* C-style comparisons
a < b, compare a b => -1
a == b, compare a b => 0
a > b, compare a b => 1
*/
compare = a: b:
if a < b
then -1
else if a > b
then 1
else 0;
/* Split type into two subtypes by predicate `p`, take all elements
of the first subtype to be less than all the elements of the
second subtype, compare elements of a single subtype with `yes`
and `no` respectively.
Example:
let cmp = splitByAndCompare (hasPrefix "foo") compare compare; in
cmp "a" "z" => -1
cmp "fooa" "fooz" => -1
cmp "f" "a" => 1
cmp "fooa" "a" => -1
# while
compare "fooa" "a" => 1
*/
splitByAndCompare = p: yes: no: a: b:
if p a
then if p b then yes a b else -1
else if p b then 1 else no a b;
/* Reads a JSON file. */
importJSON = path:
builtins.fromJSON (builtins.readFile path);
## Warnings and asserts
/* See https://github.com/NixOS/nix/issues/749. Eventually we'd like these
to expand to Nix builtins that carry metadata so that Nix can filter out
the INFO messages without parsing the message string.
Usage:
{
foo = lib.warn "foo is deprecated" oldFoo;
}
TODO: figure out a clever way to integrate location information from
something like __unsafeGetAttrPos.
*/
warn = msg: builtins.trace "WARNING: ${msg}";
info = msg: builtins.trace "INFO: ${msg}";
## Function annotations
/* Add metadata about expected function arguments to a function.
The metadata should match the format given by
builtins.functionArgs, i.e. a set from expected argument to a bool
representing whether that argument has a default or not.
setFunctionArgs : (a → b) → Map String Bool → (a → b)
This function is necessary because you can't dynamically create a
function of the { a, b ? foo, ... }: format, but some facilities
like callPackage expect to be able to query expected arguments.
*/
setFunctionArgs = f: args:
{ # TODO: Should we add call-time "type" checking like built in?
__functor = self: f;
__functionArgs = args;
};
/* Extract the expected function arguments from a function.
This works both with nix-native { a, b ? foo, ... }: style
functions and functions with args set with 'setFunctionArgs'. It
has the same return type and semantics as builtins.functionArgs.
setFunctionArgs : (a → b) → Map String Bool.
*/
functionArgs = f: f.__functionArgs or (builtins.functionArgs f);
/* Check whether something is a function or something
annotated with function args.
*/
isFunction = f: builtins.isFunction f ||
(f ? __functor && isFunction (f.__functor f));
}