mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-11-23 06:01:15 +00:00
79 lines
2.8 KiB
Nix
79 lines
2.8 KiB
Nix
rec {
|
|
|
|
# Identity function.
|
|
id = x: x;
|
|
|
|
# Constant function.
|
|
const = x: y: x;
|
|
|
|
# Named versions corresponding to some builtin operators.
|
|
concat = x: y: x ++ y;
|
|
or = x: y: x || y;
|
|
and = x: y: x && y;
|
|
mergeAttrs = x: y: x // y;
|
|
|
|
# Compute the fixed point of the given function `f`, which is usually an
|
|
# attribute set that expects its final, non-recursive representation as an
|
|
# argument:
|
|
#
|
|
# f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
|
|
#
|
|
# Nix evaluates this recursion until all references to `self` have been
|
|
# resolved. At that point, the final result is returned and `f x = x` holds:
|
|
#
|
|
# nix-repl> fix f
|
|
# { bar = "bar"; foo = "foo"; foobar = "foobar"; }
|
|
#
|
|
# See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
|
|
# details.
|
|
fix = f: let x = f x; in x;
|
|
|
|
# A variant of `fix` that records the original recursive attribute set in the
|
|
# result. This is useful in combination with the `extends` function to
|
|
# implement deep overriding. See pkgs/development/haskell-modules/default.nix
|
|
# for a concrete example.
|
|
fix' = f: let x = f x // { __unfix__ = f; }; in x;
|
|
|
|
# Modify the contents of an explicitly recursive attribute set in a way that
|
|
# honors `self`-references. This is accomplished with a function
|
|
#
|
|
# g = self: super: { foo = super.foo + " + "; }
|
|
#
|
|
# that has access to the unmodified input (`super`) as well as the final
|
|
# non-recursive representation of the attribute set (`self`). `extends`
|
|
# differs from the native `//` operator insofar as that it's applied *before*
|
|
# references to `self` are resolved:
|
|
#
|
|
# nix-repl> fix (extends g f)
|
|
# { bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
|
|
#
|
|
# The name of the function is inspired by object-oriented inheritance, i.e.
|
|
# think of it as an infix operator `g extends f` that mimics the syntax from
|
|
# Java. It may seem counter-intuitive to have the "base class" as the second
|
|
# argument, but it's nice this way if several uses of `extends` are cascaded.
|
|
extends = f: rattrs: self: let super = rattrs self; in super // f self super;
|
|
|
|
# Flip the order of the arguments of a binary function.
|
|
flip = f: a: b: f b a;
|
|
|
|
# Pull in some builtins not included elsewhere.
|
|
inherit (builtins)
|
|
pathExists readFile isBool isFunction
|
|
isInt add sub lessThan
|
|
seq deepSeq genericClosure;
|
|
|
|
# Return the Nixpkgs version number.
|
|
nixpkgsVersion =
|
|
let suffixFile = ../.version-suffix; in
|
|
readFile ../.version
|
|
+ (if pathExists suffixFile then readFile suffixFile else "pre-git");
|
|
|
|
# Whether we're being called by nix-shell.
|
|
inNixShell = builtins.getEnv "IN_NIX_SHELL" == "1";
|
|
|
|
# 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;
|
|
|
|
}
|