Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucsd!sdcc6!ir230
From: ir230@sdcc6.ucsd.edu (john wavrik)
Newsgroups: comp.lang.forth
Subject: Domain of Forth
Keywords: ANSI Questions ,  Control Constructs
Message-ID: <12354@sdcc6.ucsd.edu>
Date: 21 Aug 90 06:25:36 GMT
Organization: University of California, San Diego
Lines: 100


                            ANSI QUESTIONS

I.  Machine Readible BASIS
    I waited for a machine readible BASIS12 only to find that I would 
    need Microsoft Word to read it.

    Some postings suggest a misunderstanding of the rationale for a 
    machine readible copy of the BASIS. It is NOT to save money. 
    Downloading from GEnie, even if successful, probably costs more 
    than $10. It IS to allow people to study the document and to 
    comment upon it. It would have been nice to have some exchanges on 
    the network with quotes from the document. It would also be nice 
    to pick the document apart and put it into a database. A lot of
    the information we all have about the workings of the ANSI team is 
    hearsay and opinion -- a document in a useful form would be a good 
    tool to focus the debate.

    Suggestion: The ANSI team make available a packet consisting of 
    the printed BASIS document and a diskette with the document in 
    machine-readible form (preferably including a plain ASCII text 
    glossary file).  THIS SHOULD BE AVAILABLE IN A TIMELY FASHION SO 
    THAT USERS HAVE AMPLE TIME TO PREPARE SUBMISSIONS TO THE ANSI 
    TEAM. 

In a recent posting I gave an implementation of an algorithm about 
permutations. Three things arose that I would like to ask someone on 
the ANSI team to address. 

II. Deferred Execution
    Will the proposed ANSI standard have a portable mechanism for 
    deferred execution (like the F83 words  DEFER and IS)

III. Recursion and return stack size
    When implementing a recursive algorithm it often becomes necessary 
    to increase the size of the return stack. Will there be a portable 
    way to do this? 

    Along the same lines:  will there be words analogous to RP0, SP0,
    RP@, SP@?

IV. Language Constructs
    A major feature of Forth is the user's ability to create control 
    constructs. An extremely simple one appeared in the permutation 
    algorithm

            If( c1 e1  c2 e2 ... ck ek )If

     The ci are non-destructive conditionals (they add a flag to the 
     top of the existing stack). This construct finds the first ci which 
     tests TRUE, executes the corresponding ei and exits the construct. 
     Each ei is responsible for cleaning the stack -- the last conditional 
     is often TRUE to clean the stack if all other conditions fail.

     A.  My original implementation of this has it compile to

             handler | addr of end | c1 | e1 | ...  ck | ek 

         Where the handler employs a loop to execute the ci until it
         finds one which is TRUE.

         My impression is that the proposed ANSI Standards will not 
         provide a portable means for accessing the IP (and that code 
         which involves handlers cannot be portable). Is this correct?

     B.  In this case, the construct is easily built up from IF .. 
         ELSE .. THEN.  The following definition just uses these:

         : )IF  ;
         : IF(  0  >R     \ count the number of IFs used
               BEGIN     ' DUP  ['] )IF  <>
               WHILE     , [COMPILE] IF
                       ' , [COMPILE] ELSE
                       R> 1+ >R
               REPEAT   DROP
               R> 0 DO  [COMPILE] THEN  LOOP  ;  IMMEDIATE

         How would this be rewritten to comply with the proposed ANSI 
         Standards?

         (I'd like to emphasize that this is a very elementary and
         useful construct -- BUT I AM NOT ASKING FOR IT TO BE INCLUDED
         IN THE STANDARD -- only (1) whether the Standard will permit 
         the user to make simple constructs like this and (2) how much 
         alteration of existing code is required) 

V.  Power of Proposed Standard
    Far more significant than the controversy over certain proposed 
    words are the circulating rumors that some members of the ANSI 
    Team do not expect it to be possible to write significant programs 
    using only proposed words and programming practices. 

    Is the ANSI team willing to provide clarification, at this point, 
    as to whether or not a purpose of the proposed Standard is to 
    allow users to write significant programs portably? 

                                                  John J Wavrik 
             jjwavrik@ucsd.edu                    Dept of Math  C-012 
                                                  Univ of Calif - San Diego 
                                                  La Jolla, CA  92093