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From: wsbusup@EUTWS1.WIN.TUE.NL (Jan Stout)
Newsgroups: comp.lang.forth
Subject: Re: Functional (Applicative) Programming
Message-ID: <9103210414.AA14573@ucbvax.Berkeley.EDU>
Date: 20 Mar 91 15:51:35 GMT
References: <9103201419.AA15196@svin01.win.tue.nl>
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Jan Stout <wsbusup%EUTWS1.WIN.TUE.NL@SCFVM.GSFC.NASA.GOV>
Organization: The Internet
Lines: 63

> > These are separate issues from how often the keyword "IF" appears in
> > your program.
>
> IF is necessary. But you can try guarded commands....
> GUARDED-BEGIN <cond> : <action>
>               <cond> : <action>
>                ...       ...
> GUARDED-END
>
> If no condition is satisfied, the program aborts. If two or more conditions
 are
> satisfied the action assossiated of one of them (non-determined) will be
> executed.
>
> GUARDED-LOOP-BEGIN <cond> : <action>
>                     ...       ...
> GUARDED-LOOP-END
>
> The loop will be executed as long as there is one condition being satisfied.
> You can choose whatever behavior you want when there is more than one
 condition
> being satisfied.
>
> These are Dijinskra structeres.
What's that you said?

Dijinskra?

(Since you called him that twice I don't consider the posibility of faulty
transmission software:)

I knew Dutch is not the easiest language for a non-native, but the man
was called Dijkstra when he left this university X years ago.
Furthermore I would use the original (shorther) spelling, so the constructs
become:

IF guard0                            DO guard0
-> statement0                        -> statement0
[] guard1                            [] guard1
-> statement1                        -> statement1
   ...                                  ...
[] guardn                            [] guardn
-> statementn                        -> statementn
FI                                   OD

By the way, implementing IF/FI and DO/OD as is in Forth, will be a bit hard,
because of the prefixedness. Therefore I'd suggest a syntax like the
following:

guard0                               guard0
IF statement0 []                     DO statement0 []
guard1                               guard1
IF statement1 []                     DO statement1 []
   ...                                  ...
guardn                               guardn
IF statementn FI                     DO statementn OD

Note that when  [] gets rewritten as ELSE, you'd have a alternative
to the Baden's OF THENS and Eaker's CASE. I'll leave the implementation
pleasures to you :)

Jan Stout, Eindhoven University of Technology
           wsbusup@eutws1.win.tue.nl (for now anyway)