nixpkgs/lib/trivial.nix
Eelco Dolstra b6bac6c144
Revert "Merge pull request #48122 from zimbatm/pkg-nixos-rebuild"
This reverts commit 10addad603, reversing
changes made to 7786575c6c.

NixOS scripts should be kept in the NixOS source tree, not in
pkgs. Moving them around is just confusing and creates unnecessary
code/history churn.
2018-10-16 20:25:44 +02:00

234 lines
5.9 KiB
Nix

{ 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";
# Attempt to get the revision nixpkgs is from
revisionWithDefault = default:
let
revisionFile = "${toString ./..}/.git-revision";
gitRepo = "${toString ./..}/.git";
in if lib.pathIsDirectory gitRepo
then lib.commitIdFromGitRepo gitRepo
else if lib.pathExists revisionFile then lib.fileContents revisionFile
else default;
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
/* 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));
}