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3 points by raymyers 6091 days ago | link | parent

Here ya go, lib/treeparse.arc. Unlike the sloppy proof of concept hcase, this one might actually be useful.

This is different from parsecomb.arc in a number of ways, one being that it operates on lists and trees while parsecomb takes strings. Parsecomb also appears to be broken...



2 points by almkglor 6091 days ago | link

Thanks! I'll be reading it through a bit.

Incidentally, pg would like to conflate strings as a list of characters, so possibly with a "correct" implementation of treeparse we can still parse strings as well.

Possibly the brokenness in parsecomb currently is from the merge with arc1 and/or arc2

Edit: Hmm. Possibly you think this can be encapsulated using one of the module systems? Most of the components are functions anyway, and the existing macros end up evaluating to functions, so it may be possible to transform them to higher-level functions instead.

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2 points by raymyers 6091 days ago | link

It would be nice to put it in a module, seeing as it binds allot of useful words. I like your module1plus, but without macro support it is hard to contain this library.

The macros seq, alt, cant-see, many, and many1 may appear to be expressible as functions, but they need to be macros to reference parsers not yet created.

    (= a (alt 'y (many b)))
    ;; `b' is not bound yet, but will be by the time `a' is used.
    (= b (alt 'x (many a)))
    (parse a '(x y))

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1 point by almkglor 6091 days ago | link

Oh, bummer. I guess I got too used to lazy evaluation in Haskell.

Macro support... dang. It's kind hard to scan through the code looking for macro definitions, and then you need to have them exportable, meaning you need the original list - and exportable macros will not be able to refer to the exporting environment (bummer).

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1 point by raymyers 6088 days ago | link

Macros in packages are a hard problem, no doubt. I still wonder if some degree of macrolet hackery might do the trick.

On a brighter note, I decided to make the lazy semantics of "lib/treeparse.arc" a special case, not the default. That way, there only needs to be one macro, delay-parser. Apart from making the code cleaner, this also makes a module more feasible.

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1 point by almkglor 6088 days ago | link

The problem is an expectation like the following:

  (module
    (module-vars foo)
    (interface settings
      foo-option)
    (def foo-option arg
      (if arg
        (= foo (car arg))
        foo))
   (mac macro-using-foo body
     `(do ,foo ,@body)))
Hmm. Maybe export the macros as functions. Hmm. This also means that everything within the module has to be macro-expanded, in case macroexpansion creates a reference to a module-based macro. Aargh.

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1 point by raymyers 6091 days ago | link

On second thought, that example goes into an infinite loop. Here's a more relevant one that does not.

    (= br (filt list:cadr:car `[,(many pattern)]))
    (= pattern (alt br anything))
Mutually recursive patterns are still a bit sketchy.

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3 points by raymyers 6091 days ago | link

Neat! The efficiency police might not dig it, but I would really like to see strings as lists. Haskell does this, and I think it's a big win.

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