http://hydra.nixos.org/build/2213576

Not sure why compilation doesn't fail on other platforms...

* Simplify the representation of attributes in the AST.
* Change the behaviour of listToAttrs() in case of duplicate names.

  tree).  This saves a lot of memory.  The vector should be sorted so
  that names can be looked up using binary search, but this is not the
  case yet.  (Surprisingly, looking up attributes using linear search
  doesn't have a big impact on performance.)

  Memory consumption for

    $ nix-instantiate /etc/nixos/nixos/tests -A bittorrent.test --readonly-mode

  on x86_64-linux with GC enabled is now 185 MiB (compared to 946
  MiB on the trunk).

  a pointer to a Value, rather than the Value directly.  This improves
  the effectiveness of garbage collection a lot: if the Value is
  stored inside the set directly, then any live pointer to the Value
  causes all other attributes in the set to be live as well.

  from the old ATerm-based evaluator.

No commit message

  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.

  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.

  finished yet.

* src/libexpr/expr-to-xml.cc (nix::showAttrs): Add `location'
  parameter.  Provide location XML attributes when it's true.  Update
  callers.
  (nix::printTermAsXML): Likewise.

* src/libexpr/expr-to-xml.hh (nix::printTermAsXML): Update prototype;
  have `location' default to `false'.

* src/nix-instantiate/nix-instantiate.cc (printResult, processExpr): Add
  `location' parameter; update callers.
  (run): Add support for `--no-location'.

* src/nix-instantiate/help.txt: Update accordingly.

* tests/lang.sh: Invoke `nix-instantiate' with `--no-location' for the
  XML tests.

* tests/lang/eval-okay-toxml.exp, tests/lang/eval-okay-to-xml.nix: New
  files.

* src/libexpr/expr-to-xml.cc (nix::showAttrs): Dereference the attribute
  RHS.  Add "path", "line", and "column" XML attributes to the node when
  source location information is available.
  (nix::printTermAsXML): Likewise for functions.

  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.

  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).

    f = args @ {x, y, z}: ...;

  `args' refers to the argument as a whole, which is further
  pattern-matched against the attribute set pattern {x, y, z}.

  functions that take a single argument (plain lambdas) into one AST
  node (Function) that contains a Pattern node describing the
  arguments.  Current patterns are single lazy arguments (VarPat) and
  matching against an attribute set (AttrsPat).

  This refactoring allows other kinds of patterns to be added easily,
  such as Haskell-style @-patterns, or list pattern matching.

  Armijn Hemel.

  <derivation outPath=... drvPath=...> attrs </derivation>.  Only emit
  the attributes of any specific derivation only.  This prevents
  exponententially large XML output due to the absense of sharing.

  concatenation and string coercion.  This was a big mess (see
  e.g. NIX-67).  Contexts are now folded into strings, so that they
  don't cause evaluation errors when they're not expected.  The
  semantics of paths has been clarified (see nixexpr-ast.def).
  toString() and coerceToString() have been merged.

  Semantic change: paths are now copied to the store when they're in a
  concatenation (and in most other situations - that's the
  formalisation of the meaning of a path).  So

    "foo " + ./bla

  evaluates to "foo /nix/store/hash...-bla", not "foo
  /path/to/current-dir/bla".  This prevents accidental impurities, and
  is more consistent with the treatment of derivation outputs, e.g.,
  `"foo " + bla' where `bla' is a derivation.  (Here `bla' would be
  replaced by the output path of `bla'.)

  kind of notation for strings.

  argument.

* Optimise header file usage a bit.
* Compile the parser as C++.