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From: philm@astroatc.UUCP (Phil Mason)
Newsgroups: net.lang,net.lang.forth
Subject: Re: RRe: What's so good about FORTH?
Message-ID: <433@astroatc.UUCP>
Date: Mon, 16-Jun-86 09:46:10 EDT
Article-I.D.: astroatc.433
Posted: Mon Jun 16 09:46:10 1986
Date-Received: Wed, 18-Jun-86 02:53:28 EDT
References: <201@pyuxv.UUCP> <3700003@uiucdcsp> <132@vaxb.calgary.UUCP>
Reply-To: philm@astroatc.UUCP (Phil Mason)
Organization: Astronautics ATC, Madison, WI
Lines: 39
Keywords: FORTH, threaded-code
Xref: watmath net.lang:2485 net.lang.forth:424

In article <634@ucbcad.BERKELEY.EDU> keppel@pavepaws.UUCP (David Keppel) writes:
>In article <432@astroatc.UUCP> philm@astroatc.UUCP (Phil Mason) writes:
>>* small size : theaded-code is about a small as you can get.
>
>Pardon, but I've never quite understood what threaded-code is.
>Could somebody give me an explanation of
>	o what it is
>	o why it is fast
>	o why other major languages don't use it or don't admit to using it
>

Threaded code is a interesting concept. If you have an algorithm, and express
the algorithm with nothing but subroutine calls, one could say that the code
is threaded. In FORTH, the subroutine calls are implicit. In a high-level
(non-assembly language) routine, a list of the addresses of all of the 
component operations, in the proper order, is sufficient to describe the
operation of the routine.

Threaded code is not by its nature fast. It is amazingly compact, however.
Speed is determined by the qualities of the threaded code interpreter and
the processor on which the interpreter runs. If subroutine calls are very
expensive time-wise on the processor, threaded code will REALLY gum up the
works.

FORTH appears to be the only major language that uses threaded code as the
primary means of expressing algorithms internally. Other languages and
applications do use threaded code but by no means even close to the extent
that FORTH does. Threaded code is used for compactness and simplicity.

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