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authorEelco Dolstra <e.dolstra@tudelft.nl>2007-11-30T16·48+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2007-11-30T16·48+0000
commit6d6c68c0d29310b6eca35f58b1e68f495d6cd33a (patch)
treeeec6c3c138951f1f0cb3f9b4b1f3b3c177c31afb /doc/manual/introduction.xml
parent633518628f48fb9c06bfd570eeca6f62696aba05 (diff)
* Added a new kind of multi-line string literal delimited by two
  single quotes.  Example (from NixOS):

    job = ''
      start on network-interfaces

      start script

        rm -f /var/run/opengl-driver
        ${if videoDriver == "nvidia"        
          then "ln -sf ${nvidiaDrivers} /var/run/opengl-driver"
          else if cfg.driSupport
          then "ln -sf ${mesa} /var/run/opengl-driver"
          else ""
        }

        rm -f /var/log/slim.log

      end script
    '';

  This style has two big advantages:

  - \, ' and " aren't special, only '' and ${.  So you get a lot less
    escaping in shell scripts / configuration files in Nixpkgs/NixOS.
    The delimiter '' is rare in scripts (and can usually be written as
    "").  ${ is also fairly rare.

    Other delimiters such as <<...>>, {{...}} and <|...|> were also
    considered but this one appears to have the fewest drawbacks
    (thanks Martin).

  - Indentation is intelligently stripped so that multi-line strings
    can follow the nesting structure of the containing Nix
    expression.  E.g. in the example above 6 spaces are stripped from
    the start of each line.  This prevents unnecessary indentation in
    generated files (which sometimes even breaks things).

  See tests/lang/eval-okay-ind-string.nix for some examples.


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