Re: Best language for implementing compilers?

On Sun, 10 Mar 2019 04:13:47 -0700 (PDT), Christopher F Clark
<christopher.f.clark@compiler-resources.com> wrote:


>[tree matching] is so good (i.e. easy to use and understand) that Terence Parr
>built a whole tool (Sorcerer) to do just that to go along with his tool PCCTS
>(aka ANTLR) so that you could do it in Java. I believe in modern versions, he
>has merged both into one tool.


ANTLR did subsume the Sorceror tree parsing tool that was provided
separately with PCCTS. ANTLR also included lexer generation which
also was a separate tool in PCCTS, (and originally was not included in
the toolkit).


So ANTLR can generate lexers, LL parsers, and tree parsers all using
the same tool - and it can generate code in multiple target languages:
only the ANTLR tool itself requires Java. PCCTS only targeted C.




But ANTLR is quite different from PCCTS - their grammars are not
compatible, so it can't be said that ANTLR is just a "newer" version.
In addition, PCCTS is LL(k) and the programmer must specify required
lookahead - the tool will fail to generate a parser (or the parser it
generates won't work) if the specified lookahead is insufficient.


ANTLR uses Parr's newer LL(*) algorithm which - in the absense of an
explicit LL(k) specification - tries to automatically determine the
lookahead required. This generally works as advertised, but there are
cases where the analysis can take exponential time and/or memory, and
in some cases the generated parser is slower than when lookahead is
specified.
[Creating a good grammar still is an art form 8-)]


George

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