🚀 go-pugleaf

>   strangesucc n =	hd [x|x<-[0..];x>n];
>   ...
>   [Major collection... 21% used (3397260/15733684), 1920 msec]
>   ...
>   GC Stack Overflow !

Whats funny with this example that the stream (lazy list) in the list
comprehension can be seen as an imperative counter which is
communicated to the consumer (hd):

    x := 0;
    while (1){
      if (x > n) output(x);
      x++;
    }

We have prototyped a scheme for the compilation of streams which
(nearly) essentially result in such an imperative counter. (Its not
published, but believe, its fairly easy). Its embedded in the approach
of mixed compile-time and run-time garbage collection via the
reference counting model described in [SG91] [Sch92].

It would use constant space for the example, i.e. one cell for the
current "head" of the stream. The head becomes reused if the next
element is demanded by the consument. A stupid straight-forward
compilation would generate a run-time test for the reference counter
of the cell to prove this reusability; a simple sharing analysis would
even eliminate the test at all in the given example (it can easy
detect that their is no context which can share the stream).

Well, we have never implemented the scheme, since streams have been
dropped from the language design we consider ([Pep91]).


@InProceedings{SG92,
  author =      {Wolfram Schulte and Wolfgang Grieskamp},
  title =       {Generating {E}fficient {P}ortable {C}ode for a
                 {S}trict {A}pplicative {L}anguage},
  booktitle =   {Phoenix Seminar and Workshop on Declarative Programming},
  year =        {1992},
  publisher =   {Springer-Verlag}
}

@PhDThesis{Sch92,
  author =      {Wolfram Schulte},
  title =       {Zur {\"U}bersetzung strikter applikativer
                 {P}rogrammiersprachen},
  school =      {Techincal University of Berlin},
  year =        {1992}
}

@TechReport{Pep91a,
  author =      {P. Pepper},
  title =       {The Programming Language OPAL},
  institution = {Technical University of Berlin},
  year =        {1991},
  type =        {},
  number =      {91-04},
  month =       {Apr},
}

--
Wolfgang Grieskamp  
wg@cs.tu-berlin.de