C-interpreter, newlines as separators?

"Noel S. Gorelick" <ngorelic@speclab.cr.usgs.gov>
Fri, 28 Apr 1995 19:44:51 GMT

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Related articles
C-interpreter, newlines as separators? ngorelic@speclab.cr.usgs.gov (Noel S. Gorelick) (1995-04-28)
Re: C-interpreter, newlines as separators? norvell@cs.toronto.edu (1995-05-09)
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Newsgroups: comp.compilers
From: "Noel S. Gorelick" <ngorelic@speclab.cr.usgs.gov>
Keywords: parse, question
Organization: Compilers Central
Date: Fri, 28 Apr 1995 19:44:51 GMT

I am writing what is turning out to be a C-like interpreter. As an
interpreter, the trailing semicolons are a nusiance, and seem kind of
silly most of the time. I would like to be able to optionally use newlines
as statement separators. My problem is shown below:

        for (i=0 ; i<10 ; i=i+1) bar(i) // works

        for (i=0 ; i<10 ; i=i+1) { // works

        for (i=0 ; i<10 ; i=i+1) // doesn't work

These three statements should all be equal, but the the newline trailing
the for() in the last one matches to an empty expression.

What I think I need to do is to conditionally ignore newlines. Only when
trying to match a 'separator' rule, should a newline not be ignored. However,
I'm not savvy enough with yacc/lex to know what I'm doing. Here are the
rules I've got:

        : separator { $$ = NULL; }
        | expression separator { $$ = $1; }

        : '\n'
        | ';'

I tried some code after matching 'expression', to disable/enable eating
of newlines, but this fails, causing the lexer to eat all newlines.

        : separator { $$ = NULL; }
        | expression { eatNL = 0; } separator { $$ = $1; eatNL = 1}

Any help would be greatly appreciated.

-- Noel (ngorelic@speclab.cr.usgs.gov)

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