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1 point by almkglor 6122 days ago | link | parent

Not sure; might actually be faster, since supposedly scheme is much more continuation-friendly than lazy-evaluation-friendly. Or not, I'm not sure

Anyway I haven't managed to wrap my head around how to implement 'seq in a continuation style; also, there's the problem of how 'cut on a parser would work in a nonlazy language - supposedly as soon as the parser given to 'cut consumes anything, 'cut will somehow dispose the 'fail continuation. I'd assume 'cut will be nearer to cut-seq, which would approximately be a cut:seq -

  (def cut-seq (parser . rest)
    (let next (seq rest)
      (fn (remaining pass fail)
        (parser
          ; since the name "remaining" is reused here,
          ; a smart compiler should be able to
          ; dispose of the outer function's remaining
          (fn (parsed remaining actions)
            (next remaining
                  (fn (parsed2 remaining actions2)
                      (pass (+ parsed parsed2)
                            remaining
                            (+ actions actions2)))
                  [err "parse error!"]]))
          fail))))
Since fail is disposed upon continuing to next (which is the rest of the sequence) everything which fail holds could then be reclaimed. 'alt's pass is its own pass, but its 'fail contains a closure.


1 point by almkglor 6122 days ago | link

The nice thing here too is that we completely lose the 'return structure. The current code keeps composing and decomposing it anyway. Hmm:

  (def filt (fun parser)
    (fn (remaining pass fail)
      (parser remaining
        (fn (parsed remaining actions)
          (pass (fun parsed) remaining actions))
        fail)))
If we assume that the base compiler isn't very optimizing (i.e. captures closures when it doesn't need to) we could use helper functions for new 'pass functions:

  (let new-pass
       (fn (fun pass)
         (fn (parsed remaining actions)
           (pass (fun parsed) remaining actions)))
    (def filt (fun parser)
      (fn (remaining pass fail)
        (parser remaining
                (new-pass fun pass)
                fail))))

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