Re: Compiler Construction in Ada

[agate!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!zaphod.mps.ohio-state]

dtl8v@holmes.acc.Virginia.EDU (Heracleitus) writes:
>...  The shift-reduce parser was
>difficult but not impossible, but coding it contributed little to the
>fundamental understanding, and table-based interpretations that led to the
>introduction of yacc helped the students to grasp the concept much better
>than coding did.  The semantic analyzer was by far the hardest part of the
>project, and unfortunately, after coding the parser and syntactic analyzer
>etc., there was little enthusiasm left for it.

I had a class experience which gave me a different perspective.  In this
class (at UMass, but not taught by Eliot :-), we implemented a subset of
ADA using Pascal; the underlying machine was a simulator that executed the
tuple form, so we could learn about machine- independent optimizations.
We wrote our own lexical analyzers, and a parser generator tool was
available, but I wrote my own instead.  I followed Chapter 6 of the
(first) Dragon Book, going from an LR(0) to an LALR(1) generator.  This
gave me a thorough understanding of LR parsing.  Since then, I have
noticed that people who use LEX and YACC and have *not* been exposed to
the gory theory tend to write bad grammars (e.g., so ambiguous that they
are hard to modify).  I have forgotten many of the details of LR parsing,
but my exposure gave me intuition about what makes a grammar good; I'm
very glad of it, since my current work is compiler-related.

Now, I still agree with Eliot and Doug.  The point of a first compiler
course is to expose CS majors to that aspect of computing, and types and
so on are very important.  But I think that anyone who wants to do real
compiler work would benefit from the experience of digging into parsers
and parser generation.

- John
--
hagerman@ece.cmu.edu
-- 
Send compilers articles to compilers@iecc.cambridge.ma.us or
{ima | spdcc | world}!iecc!compilers.  Meta-mail to compilers-request.