rec { /* 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. /* Concat two strings */ concat = x: y: x ++ y; /* boolean “or” */ or = x: y: x || y; /* boolean “and” */ and = x: y: x && y; /* 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. flip = f: a: b: f b a; # Apply function if argument is non-null mapNullable = f: a: if isNull a then a else f a; # Pull in some builtins not included elsewhere. inherit (builtins) pathExists readFile isBool isFunction isInt add sub lessThan seq deepSeq genericClosure; inherit (import ./strings.nix) fileContents; # Return the Nixpkgs version number. nixpkgsVersion = let suffixFile = ../.version-suffix; in fileContents ../.version + (if pathExists suffixFile then fileContents suffixFile else "pre-git"); # Whether we're being called by nix-shell. inNixShell = builtins.getEnv "IN_NIX_SHELL" != ""; # 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; /* Reads a JSON file. */ importJSON = path: builtins.fromJSON (builtins.readFile path); /* 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}"; }