Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!willett!ForthNet
From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Advanced Beginners
Message-ID: <592.UUL1.3#5129@willett.UUCP>
Date: 2 Mar 90 03:56:12 GMT
Organization: Latest link in the ForthNet chain.  (Pgh, PA)
Lines: 60


 Date: 02-28-90 (07:39)              Number: 1612 (Echo)
   To: NICK JANOW                    Refer#: 1610
 From: IAN GREEN                       Read: NO
 Subj: ADVANCED BEGINNERS            Status: PUBLIC MESSAGE

    OK, thanks. In the RTX docs I have, it mentions that I have a 
 FOR-NEXT loop construct, so I will use that as it seems to be vaguely 
 usable from my limited understanding of Forth. A code fragment that I 
 was given examplifies what I am aspiring to:

 HEX
 CONSTANT UART-BASE 2F8 ;       ( com2 )
 : CLEAR8250                    ( a word to reset a UART )
    6 FOR                       ( 6 registers )
       0                        ( the goose egg )
       UART-BASE                ( push the base address )
       I                        ( fetch up the loop index )
       +                        ( compute address )
       !                        ( barf because of I/O mapping ) 
    NEXT
 ;


 Now from what I understand the following is also kosher, but highly 
 wasteful of CPU cycles:

 : CLEAR8250-2                  ( mark 2 )
    3 FOR                       ( outer loop )
       2 FOR                    ( inner loop )
          0                     ( the goose egg again )
          UART-BASE             ( the invisible UART )
          I                     ( fetch up the outer loop index )
          J                     ( don't forget the inner loop )
          +                     ( compute )
          +                     ( rediculus isn't it )
          !                     ( finally )
      NEXT 
   NEXT
 ;

 From what I understand of the syntax of this basic control structure, I 
 can implement 'nested' loops to handle rasters and arrays etc. One idea 
 I have is to try to translate my fractal program into Forth as an 
 exercise. It does require floating point but as I recall, the F83 
 program has floats internally so that I should be OK.

 As for data containers I assume I can simply declare a variable as 
 follows:

 VARIABLE CONTAINER ;

 or is my syntax bogus?

 Ian Green

 NET/Mail : British Columbia Forth Board - Burnaby BC - (604)434-5886   
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