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* Added a new kind of multi-line string literal delimited by two

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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.
This commit is contained in:
Eelco Dolstra 2007-11-30 16:48:45 +00:00
parent 633518628f
commit 6d6c68c0d2
6 changed files with 235 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

15
src/libexpr/lexer.l
View file

@ -4,6 +4,7 @@
%x STRING
%x IND_STRING
%{
@ -122,6 +123,14 @@ inherit { return INHERIT; }
<STRING>\" { BEGIN(INITIAL); return '"'; }
<STRING>. return yytext[0]; /* just in case: shouldn't be reached */
\'\'(\ *\n)? { BEGIN(IND_STRING); return IND_STRING_OPEN; }
<IND_STRING>([^\$\']|\$[^\{\']|\'[^\'])+ {
yylval->t = makeIndStr(toATerm(yytext));
return IND_STR;
}
<IND_STRING>\$\{ { BEGIN(INITIAL); return DOLLAR_CURLY; }
<IND_STRING>\'\' { BEGIN(INITIAL); return IND_STRING_CLOSE; }
<IND_STRING>. return yytext[0]; /* just in case: shouldn't be reached */
{PATH} { yylval->t = toATerm(yytext); return PATH; /* !!! alloc */ }
{URI} { yylval->t = toATerm(yytext); return URI; /* !!! alloc */ }
@ -148,4 +157,10 @@ void backToString(yyscan_t scanner)
BEGIN(STRING);
}
void backToIndString(yyscan_t scanner)
{
struct yyguts_t * yyg = (struct yyguts_t *) scanner;
BEGIN(IND_STRING);
}
}