Re: Java Comment-Preserving Grammar

Chris F Clark wrote:
(snip)


> In particular, each place a whitespace or comment token is allowed, it
> is almost always optional. Unless your parser generator has been
> extended to support regular expressions (and standard Yacc/Bison is
> not, and prior to about 1985 there were no commonly available LL+RE
> tools and about 1990 no LR+RE tools), you can't express such optinal
> clauses "inline".


(snip)


Maybe it is that languages designed around yacc/bison work
that way? At the time I was thinking about PL/I, where there
are some places where spaces (or comments) are needed to separate
tokens:


            DO I=J TO K BY L;


(I believe that comments will also separate them.)


              DO/*loop*/I=J/*up*/TO/*the limit*/K/*increment*/BY L;


Then there is Fortran, with no inline comments and where
spaces aren't significant even in the middle of tokens.


assign 1.10 to the variable DO10I:


            DO 10 I=1.10


Print out ten numbers:


              DO10I=1,10
10 WRITE(6,11) I


But the science of Fortran parsers seems to be well understood.


-- glen
[In most modern languages, whitespace is optional unless the two
tokens next to each other look like one token, e.g. in 2+2 the
whitespace is optional, but in int foo it's not. PL/I has extra
excitement beyond tokenizing because it has no reserved words and
you can write IF IF=THEN THEN IF=ELSE; ELSE IF=THEN; -John]

Return to the comp.compilers page.
Search the comp.compilers archives again.