versions to available versions, or vice versa.
For example, the following compares installed versions to available
versions:
$ nix-env -qc
autoconf-2.59 = 2.59
automake-1.9.4 < 1.9.6
f-spot-0.0.10 - ?
firefox-1.0.4 < 1.0.7
...
I.e., there are newer versions available (in the current default Nix
expression) for Automake and Firefox, but not for Autoconf, and
F-Spot is missing altogether.
Conversely, the available versions can be compared to the installed
versions:
$ nix-env -qac
autoconf-2.59 = 2.59
automake-1.9.6 > 1.9.4
bash-3.0 - ?
firefox-1.0.7 > 1.0.4
...
Note that bash is available but no version of it is installed.
If multiple versions are available for comparison, then the highest
is used. E.g., if Subversion 1.2.0 is installed, and Subversion
1.1.4 and 1.2.3 are available, then `nix-env -qc' will print `<
1.2.3', not `> 1.1.4'.
If higher versions are available, the version column is printed in
red (using ANSI escape codes).
dependencyClosure { ... searchPath = [ ../foo ../bar ]; ... }
* Primop `dirOf' to return the directory part of a path (e.g., dirOf
/a/b/c == /a/b).
* Primop `relativise' (according to Webster that's a real word!) that
given paths A and B returns a string representing path B relative
path to A; e.g., relativise /a/b/c a/b/x/y => "../x/y".
determination (e.g., finding the header files dependencies of a C
file) in Nix low-level builds automatically.
For instance, in the function `compileC' in make/lib/default.nix, we
find the header file dependencies of C file `main' as follows:
localIncludes =
dependencyClosure {
scanner = file:
import (findIncludes {
inherit file;
});
startSet = [main];
};
The function works by "growing" the set of dependencies, starting
with the set `startSet', and calling the function `scanner' for each
file to get its dependencies (which should yield a list of strings
representing relative paths). For instance, when `scanner' is
called on a file `foo.c' that includes the line
#include "../bar/fnord.h"
then `scanner' should yield ["../bar/fnord.h"]. This list of
dependencies is absolutised relative to the including file and added
to the set of dependencies. The process continues until no more
dependencies are found (hence its a closure).
`dependencyClosure' yields a list that contains in alternation a
dependency, and its relative path to the directory of the start
file, e.g.,
[ /bla/bla/foo.c
"foo.c"
/bla/bar/fnord.h
"../bar/fnord.h"
]
These relative paths are necessary for the builder that compiles
foo.c to reconstruct the relative directory structure expected by
foo.c.
The advantage of `dependencyClosure' over the old approach (using
the impure `__currentTime') is that it's completely pure, and more
efficient because it only rescans for dependencies (i.e., by
building the derivations yielded by `scanner') if sources have
actually changed. The old approach rescanned every time.
(closed(closed(closed(...)))) since this reduces performance by
producing bigger terms and killing caching (which incidentally also
prevents useful infinite recursion detection).
with default values automatically. I.e., e -> e {}.
This feature makes convenience expressions such as
pkgs/system/i686-linux.nix in Nixpkgs obsolete, since we can just do
$ nix-instantiate ./pkgs/system/all-packages.nix
since all-packages.nix takes a single argument (system) that has a
default value (__thisSystem).
`removeAttrs attrs ["x", "y"]' returns the set `attrs' with the
attributes named `x' and `y' removed. It is not an error for the
named attributes to be missing from the input set.
* Make the `derivation' primitive much more lazy. The expression
`derivation attrs' now evaluates to (essentially)
attrs // {
type = "derivation";
outPath = derivation! attrs;
drvPath = derivation! attrs;
}
where `derivation!' is a primop that does the actual derivation
instantiation (i.e., it does what `derivation' used to do). The
advantage is that it allows commands such as `nix-env -qa' and
`nix-env -i' to be much faster since they no longer need to
instantiate all derivations, just the `name' attribute. (However,
`nix-env' doesn't yet take advantage of this since it still always
evaluates the `outPath' and `drvPath' attributes).
Also, this allows derivations to cyclically reference each other,
for example,
webServer = derivation {
...
hostName = "svn.cs.uu.nl";
services = [svnService];
};
svnService = derivation {
...
hostName = webServer.hostName;
};
Previously, this would yield a black hole (infinite recursion).
