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Shea Levy 18fefacf7d Dynamic attrs
This adds new syntax for attribute names:

* attrs."${name}" => getAttr name attrs
* attrs ? "${name}" => isAttrs attrs && hasAttr attrs name
* attrs."${name}" or def => if attrs ? "${name}" then attrs."${name}" else def
* { "${name}" = value; } => listToAttrs [{ inherit name value; }]

Of course, it's a bit more complicated than that. The attribute chains
can be arbitrarily long and contain combinations of static and dynamic
parts (e.g. attrs."${foo}".bar."${baz}" or qux), which is relatively
straightforward for the getAttrs/hasAttrs cases but is more complex for
the listToAttrs case due to rules about duplicate attribute definitions.

For attribute sets with dynamic attribute names, duplicate static
attributes are detected at parse time while duplicate dynamic attributes
are detected when the attribute set is forced. So, for example, { a =
null; a.b = null; "${"c"}" = true; } will be a parse-time error, while
{ a = {}; "${"a"}".b = null; c = true; } will be an eval-time error
(technically that case could theoretically be detected at parse time,
but the general case would require full evaluation). Moreover, duplicate
dynamic attributes are not allowed even in cases where they would be
with static attributes ({ a.b.d = true; a.b.c = false; } is legal, but {
a."${"b"}".d = true; a."${"b"}".c = false; } is not). This restriction
might be relaxed in the future in cases where the static variant would
not be an error, but it is not obvious that that is desirable.

Finally, recursive attribute sets with dynamic attributes have the
static attributes in scope but not the dynamic ones. So rec { a = true;
"${"b"}" = a; } is equivalent to { a = true; b = true; } but rec {
"${"a"}" = true; b = a; } would be an error or use a from the
surrounding scope if it exists.

Note that the getAttr, getAttr or default, and hasAttr are all
implemented purely in the parser as syntactic sugar, while attribute
sets with dynamic attribute names required changes to the AST to be
implemented cleanly.

This is an alternative solution to and closes #167

Signed-off-by: Shea Levy <shea@shealevy.com>
2013-12-31 20:59:49 +00:00
corepkgs Lower xz compression level 2013-09-02 13:32:51 +02:00
doc Add a toJSON primop 2013-11-19 00:04:11 +01:00
misc Rename nix-worker to nix-daemon 2012-10-03 17:59:23 -04:00
perl perl: Call loadConfFile() in doInit to avoid screwing sqlite journal mode. 2013-12-20 13:59:52 +01:00
scripts nix-shell --pure: Don't clear IN_NIX_SHELL 2013-12-30 16:59:24 +01:00
src Dynamic attrs 2013-12-31 20:59:49 +00:00
tests Dynamic attrs 2013-12-31 20:59:49 +00:00
.gitignore Remove nix-setuid-helper 2013-11-14 11:57:37 +01:00
AUTHORS * Put something in here. 2004-11-07 20:30:02 +00:00
bootstrap.sh bootstrap: Simplify & make more robust. 2011-09-06 12:11:05 +00:00
build.nix Add an experimental nix-make file 2012-05-21 09:43:01 -04:00
configure.ac Remove nix-setuid-helper 2013-11-14 11:57:37 +01:00
COPYING * Change this to LGPL to keep the government happy. 2006-04-25 16:41:06 +00:00
dev-shell Hack to clean up tests/test-tmp 2013-08-21 12:53:46 +02:00
INSTALL * Autoconf / Automake configuration and building. 2003-04-04 16:14:56 +00:00
Makefile.am Garbage collector: Don't follow symlinks arbitrarily 2013-07-12 14:03:36 +02:00
nix.spec.in Add gzip support for channel unpacking 2013-07-12 11:29:37 +02:00
README * Install documentation in $(docdir) (i.e. share/doc/nix). 2008-11-19 13:19:09 +00:00
release.nix Drop Cygwin and Solaris builds 2013-10-28 11:56:37 +00:00
substitute.mk Prevent config.h from being clobbered 2013-03-08 01:27:04 +01:00
version Bump version number 2013-11-19 14:45:19 +01:00

Nix is a purely functional package manager.  For installation and
usage instructions, please read the manual, which can be found in
`docs/manual/manual.html', and additionally at the Nix website at
<http://nixos.org/>.


Acknowledgments

This product includes software developed by the OpenSSL Project for
use in the OpenSSL Toolkit (http://www.OpenSSL.org/).