values. This improves sharing and gives another speed up.
Evaluation of the NixOS system attribute is now almost 7 times
faster than the old evaluator.
use site, allowing environments to be stores as vectors of values
rather than maps. This should speed up evaluation and reduce the
number of allocations.
precedence, i.e. `with {x=1;}; with {x=2;}; x' evaluates to 2'.
This has a simpler implementation and seems more natural. There
doesn't seem to be any code in Nixpkgs or NixOS that relies on the
old behaviour.
efficiently. The symbol table ensures that there is only one copy
of each symbol, thus allowing symbols to be compared efficiently
using a pointer equality test.
then the blackhole has to be removed to ensure that repeated
evaluation of the same value gives an assertion failure again rather
than an "infinite recursion" error.
that there are some places in Nixpkgs (php_configurable /
composableDerivation, it seems) that call `derivation' with
incorrect arguments (namely, the `name' attribute missing) but get
away with it because of laziness.
* Removed exprToString and stringToExpr because there is no ATerm
representation to work on anymore (and exposing the internals of the
evaluator like this is not a good idea anyway).
allowed. So `name1@name2', `{attrs1}@{attrs2}' and so on are now no
longer legal. This is no big loss because they were not useful
anyway.
This also changes the output of builtins.toXML for @-patterns
slightly.
broken, but now the evaluator checks for it to prevent Nix
expressions from relying on undefined behaviour. Equality tests are
implemented using a shallow pointer equality test between ATerms.
However, because attribute sets are lazy and contain position
information, this can give false positives. For instance,
previously
let y = {x = 1;}; in y == y
evaluated to true, while the equivalent expression
{x = 1;} == {x = 1;}
evaluated to false. So disallow these tests for now. (Eventually
we may want to implement deep equality tests for attribute sets,
like lib.eqStrict.)
* Idem: disallow comparisons between functions.
* Implemented deep comparisons of lists. This had the same problem as
attribute sets - the elements in the list weren't evaluated. For
instance,
["xy"] == [("x" + "y")]
evaluated to false. Now it works properly.
(which means it can only be defined via "inherit"), otherwise we get
scoping bugs, since __overrides can't be recursive (or at least, it
would be hard).
a rec. This will be very useful to allow end-user customisation of
all-packages.nix, for instance globally overriding GCC or some other
dependency. The // operator doesn't cut it: you could replace the
"gcc" attribute, but all other attributes would continue to
reference the original value due to the substitution semantics of
rec.
The syntax is a bit hacky but this is to allow backwards
compatibility.
in attribute set pattern matches. This allows defining a function
that takes *at least* the listed attributes, while ignoring
additional attributes. For instance,
{stdenv, fetchurl, fuse, ...}:
stdenv.mkDerivation {
...
};
defines a function that requires an attribute set that contains the
specified attributes but ignores others. The main advantage is that
we can then write in all-packages.nix
aefs = import ../bla/aefs pkgs;
instead of
aefs = import ../bla/aefs {
inherit stdenv fetchurl fuse;
};
This saves a lot of typing (not to mention not having to update
all-packages.nix with purely mechanical changes). It saves as much
typing as the "args: with args;" style, but has the advantage that
the function arguments are properly declared (not implicit in what
the body of the "with" uses).
