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Date: Tue, 27 Oct 92 14:42:31 EST
From: hedden@eniac.seas.upenn.edu (Jerry Hedden)
Posted-Date: Tue, 27 Oct 92 14:42:31 EST
Message-Id: <9210271942.AA00591@eniac.seas.upenn.edu>
To: caml-list@margaux
Subject: Infinite Streams in Caml Light 0.5
Sender: weis@margaux

There is a point concerning streams in Caml Light that is not
dealt with in the manual.  This involves the use of function
calls in stream patterns.  Such calls are not evaluated in a lazy
manner, and can cause the system to crash when a recursive
function is used on infinite streams.  For example, the following
function is intended to map a function over all the elements of a
stream: 

    let rec map_stream func = function
        [< 'x; (map_stream func) strm >] -> [< '(func x); strm >]
      | [< >] -> [< >]
    ;;

However, as indicated above, if `strm' is infinite, evaluation of 
the recursive call progresses ad infinitum until "out of memory"
occurs.

A version of the function that does work on infinite streams is:

    let rec map_stream func = function
        [< 'x; strm >] -> [< '(func x); map_stream func strm >]
      | [< >] -> [< >]
    ;;

In summary, caution is advised when working with function calls 
on infinite streams.  (Of course, we already knew that.  Didn't 
we?  ;-)


Jerry D. Hedden
hedden@esdsdf.dnet.ge.com