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Wed Sep 5 22:40:42 CEST 2007

monads and map

so.. what about writing a macro for this 'generalized map - not quite
a real monad - collect results in a list' pattern?

i guess this is just unfold..

no it's not..

got this macro + usage:

  (define-syntax for-collect
    (syntax-rules ()
      ((_ state-bindings
          terminate-expr
          result-expr
          state-update-exprs)
       (let next ((l '())
                  . state-bindings)
         (if terminate-expr
             (reverse! l)
             (next (cons result-expr l)
                   . state-update-exprs))))))

  (define (@unfold-iterative stream)
    (for-collect
     ((s stream))
     (@null? s)
     (@car s)
     ((@cdr s))))



but it looks just ugly, so i'm going to forget about it.. i guess, if
this pattern shows up in code, it means i'm not using a proper hof.

what about writing it as a hof instead of a macro?

i think i'm getting a bit tired.. just reinvented unfold.. no, it's
unfold*




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