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From: hirchert@uxe.cso.uiuc.edu
Newsgroups: comp.lang.fortran
Subject: Re: FORTRAN 8x parser/lexer .NE. compil
Message-ID: <50500082@uxe.cso.uiuc.edu>
Date: 20 Oct 88 17:50:00 GMT
References: <656@convex.UUCP>
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Nf-ID: #R:convex.UUCP:656:uxe.cso.uiuc.edu:50500082:000:2036
Nf-From: uxe.cso.uiuc.edu!hirchert    Oct 20 12:50:00 1988


Steve Rowan quite correctly points out that doing a lexer/parser is only a
very small part of a compiler.  Since no one who was at the Paris WG5 meeting
has explicitly confirmed whether that was all that was demonstrated or whether
the demo also included some semantic analysis (and, if so, how much), it is
difficult to say whether that demo "proved" anything about the implemetability
of Fortran 8x.

Steve then proceeded to present the following numbers, derived from the size
of the Convex Ada compiler:
  5K lines - lexing/parsing
 95K lines - semantic analysis
 80K lines - vectorization and code generation
 20K lines - dependent compilation library management

I had a little problem with these:

The local ambiguities, proliferation of derived types and operations, and
multiple symbol tables of Ada appear to me to make its semantic analysis much
harder than that of Fortran 8x.  I would put the complexity of Fortran 8x more
on a par with Modula 2 or an extended Pascal.

On the other hand, I think Steve is right on track with his concerns about the
cost of optimizing/vectorizing the array language.  If most of the opponents
of the Fortran 8x draft were expressing concerns about the amount of effort to
generate efficient code for the array language, I could take their concerns
about complexity more seriously.  Instead, I see most of those opponents
supporting the array language and a number of vendors already implementing it.

Finally, 20K for dependent compilation library management also looks high to me.
Fortran 8x's dependent compilation feature was intended to be more like a
precompiled INCLUDE than the kind of grand feature in Ada.  If there are aspects
of it that would force this kind code inflation, then they should be repaired,
but lets not throw out the baby with the bathwater.

In short, I expect Fortran 8x to be significantly more work to compile than
FORTRAN 77, but not as much work as Steve suggests.

Kurt W. Hirchert     hirchert@ncsa.uiuc.edu
National Center for Supercomputing Applications