I am writing a parser for what is effectively a C declaration syntax,
and want to add a somewhat unusual feature. Namely, I'd like to
support C/C++ single-line comments, but in certain cases I'd like to
retain comments that immediately follow a declaration.
An example is probably clearest:
struct foo // ignored comment 'foo'
{
int a; // comment on 'a' that I want in the AST
// ignored comment
int b;
// another ignored comment
};
I've written a grammar (below) that seems to do what I want, but I
have a nagging feeling that it's not the best way to do what I want.
I'm particluarly concerned that it doesn't intuitively extend to
parsing the 'foo' comment above, since my grammar relies on
MEMBER_COMMENT being prefixed with a semicolon so the lexer won't
throw it out as a CPP_COMMENT. Does anyone have any better ways to
solve this problem? Suggestions on how to match the 'foo' comment? Any
feedback is appreciated!
Thanks!
Michael
---------------------------------------------------------------------
grammar KeepSomeComments;
root : declaration* EOF
;
declaration
: 'struct' IDENTIFIER '{' member_declaration* '}' ';'
;
member_declaration
: type IDENTIFIER (';' | MEMBER_COMMENT)
;
type : 'int'
;
IDENTIFIER
: ('a'..'z'|'A'..'Z'|'_')+ ;
MEMBER_COMMENT
: ';' (' '|'\t')* '//' (~('\n'|'\r'))* NEWLINE
;
CPP_COMMENT
: '//' (~('\n'|'\r'))* NEWLINE { $channel=HIDDEN; }
;
fragment NEWLINE
: ('\n'|'\r')
;
WS : (' '|'\t'|'\n'|'\r')+ { $channel=HIDDEN; }
;
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