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authorEelco Dolstra <e.dolstra@tudelft.nl>2008-08-14T14·00+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2008-08-14T14·00+0000
commit9279174dde3e1a450e63e866d2683352dd8238d3 (patch)
tree05b5b835f143b97d150a37873641fb5d5e9a7075 /src/nix-instantiate/help.txt
parentdb4f4a842515392a6b40f5c86b2ef885c1278451 (diff)
* Added an experimental feature suggested by Andres: ellipses ("...")
  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).

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