Re: Quantum Parsing (was: Re: Parsers are easy to write)

Ever written a parser for @#%$#@ Fortran? Remember, spaces are ignored,
and there are no reserved words. So strictly speaking you can write
12 FORMAT(I) = 7
which means something abysmally different from
12 FORMAT(I)
Note that practically all existing fortran compilers complain at some
-well- perfectly legal code. Another example:
            DO 10 I=1
is an assignment of variable DO10I
            DO 10 I=1,10
is a loop.
Write a parser for that, if you like. And building a recursive thing
with backtracking and certain state values produces essentially nothing
that a parser generator could not produce. Only that you may be less
efficient. Only pretty simple grammars can be substantially faster
parsed by a handwritten parser.
[I wrote a yacc parser for Fortran, using a prepass over each statement to
decide whether it's an assignment or not. It wasn't that hard to do. It's
in the compilers archives for anyone who cares. -John]
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