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Eelco Dolstra 59b94ee18a * When something goes wrong in the evaluation of a Nix expression, 
print a nice backtrace of the stack, rather than vomiting a gigantic
  (and useless) aterm on the screen.  Example:

    error: while evaluating file `.../pkgs/system/test.nix':
    while evaluating attribute `subversion' at `.../pkgs/system/all-packages-generic.nix', line 533:
    while evaluating function at `.../pkgs/applications/version-management/subversion/default.nix', line 1:
    assertion failed at `.../pkgs/applications/version-management/subversion/default.nix', line 13

  Since the Nix expression language is lazy, the trace may be
  misleading.  The purpose is to provide a hint as to the location of
  the problem.
 2004-04-05 22:27:41 +00:00
Eelco Dolstra c4ac2a164a * The recent change in nixpkgs of calling `stdenv.mkDerivation' 
instead of `derivation' triggered a huge slowdown in the Nix
  expression evaluator.  Total execution time of `nix-env -qa' went up
  by a factor of 60 or so.

  This scalability problem was caused by expressions such as

    (x: y: ... x ...) a b

  where `a' is a large term (say, the one in
  `all-packages-generic.nix').  Then the first beta-reduction would
  produce

    (y: ... a ...) b

  by substituting `a' for `x'.  The second beta-reduction would then
  substitute `b' for `y' into the body `... a ...', which is a large
  term due to `a', and thus causes a large traversal to be performed
  by substitute() in the second reduction.  This is however entirely
  redundant, since `a' cannot contain free variables (since we never
  substitute below a weak head normal form).

  The solution is to wrap substituted terms into a `Closed'
  constructor, i.e.,

    subst(subs, Var(x)) = Closed(e) iff subs[x] = e

  have substitution not descent into closed terms,

    subst(subs, Closed(x)) = Closed(x)

  and otherwise ignore them for evaluation,

    eval(Closed(x)) = eval(x).

* Fix a typo that caused incorrect substitutions to be performed in
  simple lambdas, e.g., `(x: x: x) a' would reduce to `(x: a)'.
 2004-03-30 15:05:35 +00:00
Eelco Dolstra ac4d39f9db * Added an operator `?' to test for attribute existence, e.g., 
`attrs ? x' yields true iff `attrs' has an attribute named `x'.
 2004-03-28 21:15:01 +00:00
Eelco Dolstra f958bcdf1f * Added an operator `~' to select paths within a derivation. E.g., 
{stdenv, bash}: derivation {
      builder = bash ~ /bin/sh;
      args = ["-e" "-x" ./builder.sh];
      ...
    }

  Here the attribute `builder' will evaluate to, e.g.,
  `/nix/store/1234abcd...-bash-2.0.1/bin/sh'.
 2004-03-28 20:58:28 +00:00
Eelco Dolstra db3e644c1c * Added plain lambdas, e.g., `let { id = x: x; const = x: y: x; }'. 
`bla:' is now no longer parsed as a URL.

* Re-enabled support for the `args' attribute in derivations to
  specify command line arguments to the builder, e.g.,

    ...
    builder = /usr/bin/python;
    args = ["-c" ./builder.py];
    ...
 2004-03-28 20:34:22 +00:00
Eelco Dolstra 79bb0008ec * `null' is a normal form. 2004-03-19 14:45:45 +00:00
Eelco Dolstra fbc48a469c * Inherited attributes in recursive attribute sets are in scope of the 
non-inherited attributes.
 2004-02-16 09:18:35 +00:00
Eelco Dolstra 9d25466b34 * An attribute set update operator (//). E.g., 
{x=1; y=2; z=3;} // {y=4;}  =>  {x=1; y=4; z=3;}
 2004-02-04 16:49:51 +00:00
Eelco Dolstra 9b44480612 * Use a map to lookup primops. 
* Various performance improvements in the evaluator.
* Do not link against unused (and missing!) libraries (-lsglr, etc.).
 2004-02-04 16:03:29 +00:00
Eelco Dolstra c4f7ae4aa5 * Verify that all variables in a Nix expression are defined. 2004-02-03 14:45:34 +00:00
Eelco Dolstra 1c9c0a5a46 * Added syntactic sugar to the construction of attribute sets to 
`inherit' variables from the surrounding lexical scope.

  E.g.,

    {stdenv, libfoo}: derivation {
      builder = ./bla;
      inherit stdenv libfoo;
      xyzzy = 1;
    }

  is equivalent to

    {stdenv, libfoo}: derivation {
      builder = ./bla;
      stdenv = stdenv;
      libfoo = libfoo;
      xyzzy = 1;
    }

  Note that for mutually recursive attribute set definitions (`rec
  {...}'), this also works, that is, `rec {inherit x;}' is equivalent
  to `let {fresh = x; body = rec {x = fresh;};}', *not*
  `rec {x = x}'.
 2004-02-02 21:39:33 +00:00
Eelco Dolstra c5baaafae6 * Replaced the SDF parser by a substantially faster Bison/Flex 
parser (roughly 80x faster).

  The absolutely latest version of Bison (1.875c) is required for
  reentrant GLR support, as well as a recent version of Flex (say,
  2.5.31).  Note that most Unix distributions ship with the
  prehistoric Flex 2.5.4, which doesn't support reentrancy.
 2004-01-30 15:21:42 +00:00
Eelco Dolstra 447089a5f6 * Catch SIGINT to terminate cleanly when the user tries to interrupt 
Nix.  This is to prevent Berkeley DB from becoming wedged.

  Unfortunately it is not possible to throw C++ exceptions from a
  signal handler.  In fact, you can't do much of anything except
  change variables of type `volatile sig_atomic_t'.  So we set an
  interrupt flag in the signal handler and check it at various
  strategic locations in the code (by calling checkInterrupt()).
  Since this is unlikely to cover all cases (e.g., (semi-)infinite
  loops), sometimes SIGTERM may now be required to kill Nix.
 2004-01-15 20:23:55 +00:00
Eelco Dolstra 6e8c19714a * Allow integer bindings in derivations. 2003-11-25 12:05:48 +00:00
Eelco Dolstra ac68840e79 * Refactoring: put the Nix expression evaluator in its own library so 
that it can be used by multiple programs.
 2003-11-19 11:35:41 +00:00
Renamed from src/nix-instantiate/eval.cc (Browse further)