🚀 go-pugleaf

doerr@inf.fu-berlin.de (Heiko Doerr) writes:

>While looking for data structures to store states of a computation
>the following questions arose concerning the garbage collector of
>Miranda. ...

>2) Is the garbage collector non-deterministic or can the following effect
>be predicted?
> 
>Once you evaluate the expressions "#(list 50000)" and "#[0..50000]"
>several times you will notice that the evaluation does not succeed all
>the times. Could anybody tell me whether and if so how the garbage
>collector is related to the operating system to explain this
>non-deterministic behaviour.

My experience from 2 years ago suggests that it is rather
nondeterministic (in the SUN 4 version, at any rate).  Maybe the
garbage collector looks at the (C?) stack and conservatively assumes
every word found there to be a heap pointer.  If some of those words
are not heap pointers but integers, arbitrary amounts of garbage will
not be collected.  Note that this is safe, but quite confusing for the
functional programmer whose program uses widely varying amounts of
storage.  

>These runs were executed on SUN-4 with 16 MB and Miranda version 2.014.

Try the VAX implementation.

Peter (almost merely guessing --- I can't find the relevant notes)
--
Peter Sestoft   *   sestoft@id.dth.dk   *   Department of Computer Science
Technical University of Denmark, Building 344      DK-2800 Lyngby, Denmark
Tel: +45 45 93 33 32 * Direct: +45 45 93 12 22/3749 * Fax: +45 42 88 45 30