|"Bootstrapping yacc in yacc" -> "Bootstrapping yacc in lex"! firstname.lastname@example.org (Rock Brentwood) (2021-03-14)|
|Re: "Bootstrapping yacc in yacc" -> "Bootstrapping yacc in lex"! email@example.com (Kaz Kylheku) (2021-03-15)|
|From:||Kaz Kylheku <firstname.lastname@example.org>|
|Date:||Mon, 15 Mar 2021 02:37:16 -0000 (UTC)|
|Organization:||A noiseless patient Spider|
|Injection-Info:||gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="83188"; mail-complaints-to="email@example.com"|
|Posted-Date:||15 Mar 2021 11:52:38 EDT|
On 2021-03-15, Rock Brentwood <firstname.lastname@example.org> wrote:
> It's a recurrent question that's come up in other forums "can yacc be
> bootstrapped in yacc?" Now, I'm adding a twist.
> I'll repeat one of my recent replies here. In the syntax for yacc files, laid
> out by the POSIX standard, there is no mandatory semi-colon at the ends of
> rules, so an extra look-ahead is required to determine whether an identifier
> is followed by a colon. If so, then this indicates the left-hand side of a new
> A grammar rule has the form
> left-hand-side ":" stuff on the right optional ";"'s.
> If you see a ":" in the middle of the rules on the right, then you've actually
> sneaked on over into the *next* rule.
> Bison hacks the syntax, by making left-hand-side + ":" into a single token.
You could simply allow rules of this form
":" right side ...
With a semantic restrction that this must be preceded by a rule that
is not terminated with a semicolon, whose last element is a symbol:
blah ":" previous rule material ending in symbol /* no semicolon */
":" next rule ";"
Then we make the AST transformation of moving "symbol" to be the head
of the following rule:
blah ":" previous rule material ending in
symbol ":" next rule ";"
Situations where it's not a symbol, or the prior rule has ended in
a semicolon (which is thus followed by a colon) are not syntax
errors, but are diagnosed semantically.
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
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