c20cc6d0b3
Putting information in external JSON files is IMHO not an improvement over the idiomatic style of Nix expressions. The use of JSON doesn't add anything over Nix expressions (in fact it removes expressive power). And scattering package info over lots of little files makes packages less readable over having the info in one file.
123 lines
4.3 KiB
Nix
123 lines
4.3 KiB
Nix
rec {
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# Identity function.
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id = x: x;
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# Constant function.
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const = x: y: x;
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# Named versions corresponding to some builtin operators.
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concat = x: y: x ++ y;
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or = x: y: x || y;
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and = x: y: x && y;
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mergeAttrs = x: y: x // y;
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# Compute the fixed point of the given function `f`, which is usually an
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# attribute set that expects its final, non-recursive representation as an
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# argument:
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#
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# f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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#
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# Nix evaluates this recursion until all references to `self` have been
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# resolved. At that point, the final result is returned and `f x = x` holds:
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#
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# nix-repl> fix f
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# { bar = "bar"; foo = "foo"; foobar = "foobar"; }
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#
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# See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
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# details.
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fix = f: let x = f x; in x;
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# A variant of `fix` that records the original recursive attribute set in the
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# result. This is useful in combination with the `extends` function to
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# implement deep overriding. See pkgs/development/haskell-modules/default.nix
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# for a concrete example.
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fix' = f: let x = f x // { __unfix__ = f; }; in x;
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# Modify the contents of an explicitly recursive attribute set in a way that
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# honors `self`-references. This is accomplished with a function
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#
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# g = self: super: { foo = super.foo + " + "; }
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#
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# that has access to the unmodified input (`super`) as well as the final
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# non-recursive representation of the attribute set (`self`). `extends`
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# differs from the native `//` operator insofar as that it's applied *before*
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# references to `self` are resolved:
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#
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# nix-repl> fix (extends g f)
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# { bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
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#
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# The name of the function is inspired by object-oriented inheritance, i.e.
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# think of it as an infix operator `g extends f` that mimics the syntax from
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# Java. It may seem counter-intuitive to have the "base class" as the second
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# argument, but it's nice this way if several uses of `extends` are cascaded.
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extends = f: rattrs: self: let super = rattrs self; in super // f self super;
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# Create an overridable, recursive attribute set. For example:
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#
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# nix-repl> obj = makeExtensible (self: { })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; extend = «lambda»; }
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#
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# nix-repl> obj = obj.extend (self: super: { foo = "foo"; })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
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#
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# nix-repl> obj = obj.extend (self: super: { foo = super.foo + " + "; bar = "bar"; foobar = self.foo + self.bar; })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
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makeExtensible = makeExtensibleWithCustomName "extend";
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# Same as `makeExtensible` but the name of the extending attribute is
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# customized.
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makeExtensibleWithCustomName = extenderName: rattrs:
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fix' rattrs // {
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${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);
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};
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# Flip the order of the arguments of a binary function.
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flip = f: a: b: f b 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 isFunction
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isInt add sub lessThan
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seq deepSeq genericClosure;
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inherit (import ./strings.nix) fileContents;
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# Return the Nixpkgs version number.
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nixpkgsVersion =
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let suffixFile = ../.version-suffix; in
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fileContents ../.version
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+ (if pathExists suffixFile then fileContents suffixFile else "pre-git");
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# Whether we're being called by nix-shell.
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inNixShell = builtins.getEnv "IN_NIX_SHELL" != "";
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# Return minimum/maximum of two numbers.
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min = x: y: if x < y then x else y;
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max = x: y: if x > y then x else y;
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/* Reads a JSON file. */
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importJSON = path:
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builtins.fromJSON (builtins.readFile path);
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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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Usage:
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{
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foo = lib.warn "foo is deprecated" oldFoo;
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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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*/
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warn = msg: builtins.trace "WARNING: ${msg}";
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info = msg: builtins.trace "INFO: ${msg}";
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}
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