[Haskell-cafe] iterative algorithms: how to do it in Haskell?

Tamas K Papp tpapp at Princeton.EDU
Wed Aug 16 09:06:12 EDT 2006


I am a newbie learning Haskell.  I have used languages with functional
features before (R, Scheme) but not purely functional ones without

Most of the programming I do is numerical (I am an economist).  I
would like to know how to implement the iterative algorithm below in

f is an a->a function, and there is a stopping rule 
goOn(a,anext) :: a a -> Bool which determines when to stop.  The
algorithm looks like this (in imperative pseudocode):

a = ainit

while (true) {
      anext <- f(a)
      if (goOn(a,anext))
      	 a <- anext
         stop and return anext

For example, f can be a contraction mapping and goOn a test based on
the metric.  I don't know how to do this in a purely functional
language, especially if the object a is large and I would like it to
be garbage collected if the iteration goes on.

Thank you,


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