Re: macro expansion ?

From	Chris Hinsley <chris.hinsley@gmail.com>
Newsgroups	comp.lang.forth
Date	2011-06-29 19:32 +0100
Message-ID	<2011062919320387546-chrishinsley@gmailcom> (permalink)
References	(3 earlier) <20110628185151666-chrishinsley@gmailcom> <2011062819022446632-chrishinsley@gmailcom> <2011062819111570841-chrishinsley@gmailcom> <iufj50$tct$1@dont-email.me> <iufm7g$kf4$1@dont-email.me>
Subject	Re: macro expansion ?

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On 2011-06-29 18:09:49 +0100, Gerry Jackson said:

> On 29/06/2011 17:17, Gerry Jackson wrote:
>> On 28/06/2011 19:11, Chris Hinsley wrote:
>>> On 2011-06-28 19:02:24 +0100, Chris Hinsley said:
>>> 
>> 
>> [...]
>> 
>>>> How about a macro that did greatest common divider ?
>>>> 
>>>> Function gcd(a As Integer, b As Integer) As Integer
>>>> If b = 0 Then
>>>> gcd = a
>>>> Else
>>>> gcd = gcd(b,a)
>>>> End If
>>>> End Function
>>>> 
>>>> Chris
>>> 
>>> I think I'm rapidly getting into the 'but you wouldn't do it like that'
>>> teritory. You'd just define a word that did the calcutation, and then
>>> use it with somthing like [ 15 5 GCD ] LITERAL.
>>> 
>>> But I'm pushing the issue of how you'd do it with a macro called GCD to
>>> expose the limits.
>>> 
>> 
>> Andrew & Anton have given you good reasons not to do it via a macro, but
>> if you really want to have a gcd macro it's not difficult e.g an
>> interpret time macro for gcd is:
>> 
>> macro gcd ?dup [if] tuck mod gcd [then]"
>> cr 17 118 * 17 62 * gcd . \ Should display 34
>> 
>> To use it in a colon definition you can do
>> : t1 [ 17 118 * 17 62 * gcd ] literal ;
>> t1 . \ Should display 34
>> 
>> To pass the arguments into the colon definition requires a little more
>> trickery (for systems such as GForth that place control information on
>> the data stack and other systems that require a balanced stack between :
>> and ;) e.g.:
>> 
>> : pass >r ' execute r> ; immediate
>> 17 118 * 17 62 * pass pass : t2 [ gcd ] literal ;
>> t2 . \ Should display 34
>> 
>> Alternatively [gcd] can be defined as a macro:
>> 
>> macro [gcd] [ ?dup [if] tuck mod [gcd] [else] ] [then]"
>> 17 177 * 17 93 * pass pass : t3 [gcd] literal ;
>> t3 . \ should display 51
>> 
>> It all works with GForth
>> 
> 
> Incidentally the gcd calculation can be done in interpret mode without 
> a macro e.g.
> 
> 51 59 * 51 31 *
> ?dup [if] tuck mod 0 >in ! [then] .

Neat !

This sort of thing is the mind bending stuff I like about Forth. !

Chris

Thread

macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 14:43 +0100
  Re: macro expansion ? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-06-28 10:58 -0500
    Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 18:34 +0100
      Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 18:51 +0100
        Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 19:02 +0100
          Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 19:11 +0100
            Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 19:17 +0100
              Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 19:47 +0100
                Re: macro expansion ? Josh Grams <josh@qualdan.com> - 2011-06-29 15:34 +0000
                Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-29 19:21 +0100
            Re: macro expansion ? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-06-29 03:15 -0500
              Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-29 13:11 +0100
            Re: macro expansion ? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-06-29 17:17 +0100
              Re: macro expansion ? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-06-29 18:09 +0100
                Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-29 19:32 +0100
                Re: macro expansion ? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-07-02 08:48 +0100
    Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-29 00:44 +0100
    Re: macro expansion ? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-06-29 20:39 +0100
  Re: macro expansion ? Elizabeth D Rather <erather@forth.com> - 2011-06-28 08:59 -1000
    Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 20:39 +0100
      Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-28 21:34 +0100
        Re: macro expansion ? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-06-29 03:26 -0500
  Re: macro expansion ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-06-29 11:25 +0000
    Re: macro expansion ? Chris Hinsley <chris.hinsley@gmail.com> - 2011-06-29 13:24 +0100
      Re: macro expansion ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-07-03 14:02 +0000
    Re: macro expansion ? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2011-06-29 18:48 +0000
  Re: macro expansion ? BruceMcF <agila61@netscape.net> - 2011-06-30 11:11 -0700
  Re: macro expansion ? Ian Osgood <iano@quirkster.com> - 2011-07-02 16:22 -0700
  Re: macro expansion ? Hugh Aguilar <hughaguilar96@yahoo.com> - 2011-07-05 17:35 -0700

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