Re: Hand written or tool generated lexical analyzers for FORTRAN

Fred J. Scipione wrote:


(snip)


> This discussion has reminded me of a thought I had following the
> expositions in this news group on Quantum Parsers and Quantum
> Grammars. You may recall (or look-up :-)) that the threads included
> demonstrations of the idea that there is an algebra for parser
> descriptions that allows both the language terms and action items
> (code segments) to be manipulated without changing their semantics (or
> at least that is my poor paraphrasing of one of the demonstrated
> ideas).


And your discussion reminded me of dynamic programming algorithms. I
believe they are often used in code generators, to find the optimal
code sequence for a given function.


I was just thinking, though, that they could be used in a parser. In
case of a syntax error one could find the closest legal syntax to the
input statement. I have known compilers to attempt to correct the
input, but I don't know that they used dynamic programming.


The IBM PL/I(F) compiler was pretty good, with messages like
"Semicolon missing, one inserted".


I still remember when I was just learning Fortran and asked someone a
question about it, they commented about a compiler that didn't
understand the FROMAT statement.


-- glen

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