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From: gateley@m2.csc.ti.com (John Gateley)
Newsgroups: comp.lang.modula2
Subject: Re: Recursive data types
Message-ID: <77390@ti-csl.csc.ti.com>
Date: 11 May 89 15:25:22 GMT
References: <5734@cs.Buffalo.EDU: <1046@gmdzi.UUCP> <11188@polyslo.CalPoly.EDU>
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Reply-To: gateley@m2.UUCP (John Gateley)
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In article <11188@polyslo.CalPoly.EDU> mlind@polyslo.CalPoly.EDU (Mark William Lind I) writes:
>This is dynamic memory allocation... but this is not a RECURSIVE
>data type.  Personally, I don't see what the use of a recursive
>data structure is.  Dynamic memory allocation is of obvious
>worth (no pun intended), but I don't see what the hell you would
>do with a recursive boolean expression?....... huh?

Hello Mark,

This is not a recursive boolean expression, but it is a recursive
data structure based on a recursive datatype.

Have a datatype: infinite-list. There are three operations:
head, tail, and cons (add an element). Now, we can define
the Fibonacci numbers as an infinite list, the first two elements are
1, each succeeding element is the sum of the two previous elements.
Even though the list is infinite, the program will actually only use
a finite (but arbitrarily large) portion of it. I think this might
be a recursive data type.

Disclaimer: this idea comes from Lisp/Scheme streams. It doesn't have much
to do with Modula2.

John
gateley@tilde.csc.ti.com