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From: rob@idacom.uucp (Rob Chapman)
Newsgroups: comp.lang.forth
Subject: Re: Domain of Forth
Message-ID: <1990Aug30.193536.26356@idacom.uucp>
Date: 30 Aug 90 19:35:36 GMT
Organization: IDACOM, a division of Hewlett-Packard
Lines: 55


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

 I posted a possible word BIND ( tic-token \ tic-token -- ) which would allow
 the same functionality of DEFER and IS.  It would allow the choice of early
 binding as well.

> IV. Language Constructs

>      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've always found [COMPILE] things confusing especially when COMPILE is
 included as well.  Rewriting the definition for IF( to make it ANS
 Forthable:
          : IF(  0  >R     \ count the number of IFs used
                BEGIN     ' DUP  ['] )IF  <>
                WHILE     COMPILE-TOKEN  ['] IF EXECUTE
                        ' COMPILE-TOKEN  ['] ELSE EXECUTE
                        R> 1+ >R
                REPEAT   DROP
                R> 0 DO  ['] THEN EXECUTE  LOOP  ;  IMMEDIATE

 When I'm explaining the delayed execution of immediate words to people,
 I find it clearer by using:
   ' something EXECUTE  (we use the state smart definition of ' from figForth)

 It is complementary to:
   ' something COMPILE

 As an example, this might be the definition of OF for a case extension:
   : OF  ( ? )
      ' OVER COMPILE  ' = COMPILE  ' IF EXECUTE  ' DROP COMPILE ; IMMEDIATE

 Note:
  Our COMPILE is the equivelant to the ANS Forth COMPILE-TOKEN which takes
  a tic-token off the stack and compiles a call to it.  ( If I miss the mark
  on quoting ANS Forth, its because its from memory).  Its a pity that
  COMPILE was initially defined as a look-ahead-at-runtime construct.

Rob