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From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Advanced Beginners
Message-ID: <582.UUL1.3#5129@willett.UUCP>
Date: 1 Mar 90 02:02:35 GMT
Organization: Latest link in the ForthNet chain.  (Pgh, PA)
Lines: 30


 Date: 02-27-90 (10:02)              Number: 1609 (Echo)
   To: IAN GREEN                     Refer#: 1608
 From: STEVE PALINCSAR                 Read: NO
 Subj: ADVANCED BEGINNERS            Status: PUBLIC MESSAGE

 You can't use an undefined word.  Since you're talking about variables 
 here, and since they are forth words, they need to be defined.  If you 
 tried to use an undefined word, the outer interpreter would simply give 
 you an error message.  OTOH, you don't "allocate space on the stack."  
 You put numbers on the stack, and the stack itself takes care of 
 management of the memory.  Actually, the code example given (with 
 N 1 DO ) wouldn't work with a variable (since you must use @ to get 
 the value of the variable) but would instead set up a loop that looped
 from 1 to 1 less than the numeric value of the address of the variable 
 N, which isn't what you wanted to do at all!  OTOH some forths have a 
 data structure called a VAR which instead of returning its address on 
 the stack when it is invoked instead returns the value stored at that 
 address.  Forth constants also return the value instead of the address.

 It's also useful to know that you aren't dealing with variables in a 
 loop.  The actual values for the starting and ending points of the loop 
 _as numbers_ must be on the parameter stack, since DO wants two 
 arguments; and DO puts those two values on the return stack.  Similarly,
 I (which gets at the current index of the inner loop) and J (which gets 
 at the current index of the outer loop) are not variables either, but 
 instead are words which copy the current index value from the Rstack.
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