Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #16383

Re: Using the Python Interpreter as a Reference

Show all headers | View raw

On 11/29/2011 03:12 AM, Steven D'Aprano wrote:
> On Tue, 29 Nov 2011 13:57:32 +1100, Chris Angelico wrote:
>
>> I'm inclined toward an alternative: explicit recursion. Either a
>> different syntax, or a special-case on the use of the function's own
>> name, but whichever syntax you use, it compiles in a "recurse" opcode.
>> That way, if name bindings change, it's still going to recurse -
>> something few languages guarantee, and therefore few languages can
>> optimize.
> As I recall, Forth uses (or used) a special RECURSE word which turned on
> the recursion bit while compiling, so that the compiled word could see
> itself.
>
> By memory, the (incomplete) definition:
>
> : fact dup 1- fact * ;
>
> would fail, unless you happened to already have another word called fact
> existing at compilation time. To make it recurse correctly, the compiler
> needs to make sure that the namespace fact sees includes itself:
>
> RECURSE : fact dup 1- fact * ;
>
> which should work, apart from the embarrassing fact that I don't recall
> the syntax for conditional jumps and so the recursion never terminates.
>
> :)
>
The way I remember it, the current definition was "smudged" which made 
it invisible (it basically changed the name to something unlikely) 
during the compilation.  After all, if you actually ran it at compile 
time (which was frequently done), you could fall right into 
uninitialized space.  Anyway, some implementations had an immediate 
SMUDGE word, which toggled the smudge bit and made it visible again.

Other implementations had an immediate word RECURSE, which compiled in 
whatever word was being currently defined.
I'm pretty sure neither FIG nor Forth79 had either of these.  But I 
don't recall the ANSI standard (X3J14 ?), even though I was officially 
an observer.  I can't even remember what happened to my printed copy of 
the standard.

The easiest word for conditional is IF/ELSE/THEN.   IF will skip to the 
ELSE or THEN if the condition is false.  So something resembling:

: fact dup 1- dup 0<> if recurse * then ;

might do it.  That's very rough, however.  It's been a long time.

-- 

DaveA

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-20 16:46 -0800
  Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-21 13:33 +1100
    Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-21 05:44 +0000
      Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-21 17:48 +1100
      Re: Using the Python Interpreter as a Reference Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-11-21 10:03 -0800
      Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-21 16:07 -0800
  Re: Using the Python Interpreter as a Reference Alan Meyer <ameyer2@yahoo.com> - 2011-11-22 13:37 -0500
    Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-25 02:55 -0800
      Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-25 22:10 +1100
  Re: Using the Python Interpreter as a Reference rusi <rustompmody@gmail.com> - 2011-11-25 09:11 -0800
    RE: Using the Python Interpreter as a Reference "Sells, Fred" <fred.sells@adventistcare.org> - 2011-11-25 23:22 -0500
    Re: Using the Python Interpreter as a Reference Matt Joiner <anacrolix@gmail.com> - 2011-11-26 23:19 +1100
  Re: Using the Python Interpreter as a Reference Alec Taylor <alec.taylor6@gmail.com> - 2011-11-27 05:46 +1100
  Re: Using the Python Interpreter as a Reference Rick Johnson <rantingrickjohnson@gmail.com> - 2011-11-26 10:53 -0800
    Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-27 06:34 +1100
      Re: Using the Python Interpreter as a Reference Rick Johnson <rantingrickjohnson@gmail.com> - 2011-11-26 13:15 -0800
    Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-27 14:21 -0800
      Re: Using the Python Interpreter as a Reference Colin Higwell <colinh@somewhere.invalid> - 2011-11-27 23:02 +0000
      Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-27 23:55 +0000
        Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-28 11:26 +1100
        Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-28 10:03 -0800
        Re: Using the Python Interpreter as a Reference Ian Kelly <ian.g.kelly@gmail.com> - 2011-11-28 12:32 -0700
          Re: Using the Python Interpreter as a Reference Neil Cerutti <neilc@norwich.edu> - 2011-11-28 20:20 +0000
            Re: Using the Python Interpreter as a Reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-11-29 09:48 +1300
              Re: Using the Python Interpreter as a Reference Neil Cerutti <neilc@norwich.edu> - 2011-11-28 21:11 +0000
          Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-28 13:34 -0800
          Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-28 22:24 +0000
            Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-29 09:48 +1100
            Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-28 18:42 -0800
              Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-29 13:57 +1100
                Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-29 08:12 +0000
                Re: Using the Python Interpreter as a Reference Dave Angel <d@davea.name> - 2011-11-29 03:53 -0500
              Re: Using the Python Interpreter as a Reference Ian Kelly <ian.g.kelly@gmail.com> - 2011-11-28 21:56 -0700
        Re: Using the Python Interpreter as a Reference DevPlayer <devplayer@gmail.com> - 2011-11-28 16:54 -0800
          Re: Using the Python Interpreter as a Reference DevPlayer <devplayer@gmail.com> - 2011-11-28 16:59 -0800
          Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-29 12:49 +1100
            Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-28 19:00 -0800
            Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-29 08:04 +0000
              Re: Using the Python Interpreter as a Reference DevPlayer <devplayer@gmail.com> - 2011-12-01 10:03 -0800
                Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-02 00:43 +0000
                Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-12-02 13:02 +1100
                RE: Using the Python Interpreter as a Reference "Sells, Fred" <fred.sells@adventistcare.org> - 2011-12-02 15:29 -0500
                Re: Using the Python Interpreter as a Reference Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-02 15:58 -0500
      Re: Using the Python Interpreter as a Reference Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-11-29 09:40 +1300
        Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-28 13:29 -0800
          Re: Using the Python Interpreter as a Reference Chris Angelico <rosuav@gmail.com> - 2011-11-29 08:57 +1100
          Re: Using the Python Interpreter as a Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-28 22:57 +0000
            Re: Using the Python Interpreter as a Reference Travis Parks <jehugaleahsa@gmail.com> - 2011-11-28 18:57 -0800

csiph-web