Stackless & String-processing

[Graham Matthews]

<graham at sloth.math.uga.edu> wrote:
> expression parsers as primitive parsers". There is no need for the compiler
> to "solve the halting problem". The programmer is free to use regular
> expression/automaton techniques where he/she wants. Such parsers take
> strings and return ASTs. They can then be combined with other parsers
> as if they were primitive parsers.
Fernando Pereira (pereira at research.att.com) wrote:
: One last try. I understood your point from the beginning. However, you
: did not understood *mine*. If you push the complex
: pattern-matching/parsing machinery into black boxes, there's not much
: for the monadic glue to do, is there? 

What your combinators do depends on your application. If all you are
doing is parsing using primitive automaton based parsers then your
combinators won't have much to do. But if you are doing more than
that then they will have more to do, and hence be more complex. For
example you can use the same combinators you define for parsing to do
type checking, model state, etc -- things I would not want to do with
an automaton. That is why I said that combinators are really sequencing
constructs.

Fernando Pereira (pereira at research.att.com) wrote:
: And even then, some
: optimizations, those involving the various black boxes, will be
: blocked. Here's a simple example. Assume that there are two black boxes
: A and B, and that you use monadic glue to say "A or B". A and B may be
: deterministic, but the result will not be, and exhaustive search will
: be required in the glue. Sure, I can recognize such cases by hand and
: create a new black box "A or B" which is optimized, but that is an
: error-prone hand optimization. And one may not notice subtler
: inefficiencies.

Your point appears to be that if you were programming only using automaton
for parsing you wouldn't miss the above optimisation, but that somehow
using combinators means you would miss the above optimisation. You
and I must program differently then. If I were using automaton, even
in the context of also using combinators, I would be aware of the
potential for such optimisations and look for them.

graham
-- 
            The girls is all salty, the boys is all sweet, 
                      the food ain't too shabby 
                    an' they piss in the streets
    In France, way down in France, way on down, way on down in France