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From: UNBCIC@BRFAPESP.BITNET
Newsgroups: comp.lang.forth
Subject: Guarded Commands
Message-ID: <9103210417.AA14672@ucbvax.Berkeley.EDU>
Date: 20 Mar 91 18:55:00 GMT
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Reply-To: UNBCIC%BRFAPESP.BITNET@SCFVM.GSFC.NASA.GOV
Organization: The Internet
Lines: 57

> > 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.

*PLEASE* forgive me. I *SWEAR* that, if I had time, I would look for the
correct information. I'm not sure that the first example was him. And I knew I
would probably mispell the name. But.....

> 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 :)

No way. As I don't have time, I'll not implement, but I assure you that they
can be implemented, with the same syntax in 5 lines each. Se, the IF (we should
change the IF and DO names) puts a flag on stack, that is tested by FI. This
flag is initialized (by IF) with 0. The -> can be a POSTPONE IF POSTPONE R>
POSTPONE DROP POSTPONE TRUE POSTPONE >R, and [] an alias for THEN. Same kind of
behavior for DO ... OD.

> Jan Stout, Eindhoven University of Technology

Thank you *VERY* much for the correction.

                              (8-DCS)
Daniel C. Sobral
UNBCIC@BRFAPESP.BITNET