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Re: Recognizers

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On 1/22/2017 01:42, Alex wrote:
> Some recognizer observations.

Refer to http://amforth.sourceforge.net/pr/Recognizer-rfc-C.html

3. Having R:FAIL not on the recognizer stack is inflexible. When 
supporting more than one stack, the same R:FAIL appears as the last 
implied entry in all of them, and an action like -13 THROW may not be 
right for every situation. E.g. I may want to support forward 
definitions on "not found" rather than throw an error.

The solutions would appear to be:

a. Modify the R:FAIL table when switching stacks. Messy and requires 
setting 3 entries in the table at R:FAIL and the value of 
FORTH-RECOGNIZER. Very difficult to manage, especially when recovery in 
CATCH might require restoring the default recognition stack.

b. Require each stack to have its own R:FAIL equivalent action as the 
last entry in the stack. There are some objections raised in the RfD at 
"FLAGS, R:FAIL or EXCEPTIONS".

c. Maintain the current R:FAIL but avoid executing it by adding an 
R:FAIL<this stack> to the bottom of those stacks that require it with 
SET-RECOGNIZERS to catch unresolved requests.

Given that I believe the stack will only infrequently change dynamically 
and that I'll be using mainly static FORTH-RECOGNIZERs, I'm going to use 
approach C and have a "catch all" before the built-in R:FAIL.

My application for this is meta-compilation. While generating code 
during meta-compilation I'm using a META-RECOGNIZER stack, and the 
actions of the standard REC:NAME, REC:NUM etc are metacompilation 
actions META:NAME and META:NUM, and I wish to use R:FAIL (now META:FAIL 
prior to the default R:FAIL) to provide forward declarations without 
having to declare them in advance.

Standard stack:

' REC:NAME ' REC:NUM 2 FORTH-RECOGNIZER SET-RECOGNIZERS

Meta stack:

4 RECOGNIZER META-RECOGNIZER
' META:FAIL ' META:NAME ' META:NUM 3 META-RECOGNIZER SET-RECOGNIZERS


4. Varying stack item counts from REC:<name> words.

This one has caused me a lot of grief while debugging.

: rec:num ( addr u -- d r:num | r:fail )



5. Names.

I haven't found a use for R>COMP R>INT or R>POST. Also, the names are a 
little suspect; why not match NAME>X and have R>INTERPRET R>COMPILE and 
R>POSTPONE (if they are required).

R:<name> (a table) and REC:<name> (a word) are too similar, and an 
attempt has been made to semi-standardize them.

RECOGNIZER would be clearer as RECOGNIZER-STACK

DO-RECOGNIZER I have implemented as the verb RECOGNIZE; it leads to 
pretty understandable code like this (?STACK is an underflow test on the 
data stack).

: interpreter ( -- ) \ outer interpreter
     begin ?stack parse-name dup
     while recognize execute
     repeat 2drop ;

-- 
Alex

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Recognizers Alex <alex@rivadpm.com> - 2017-01-22 01:42 -0500
  Re: Recognizers Matthias Trute <matthias.trute@gmail.com> - 2017-01-22 03:06 -0800
  Re: Recognizers anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-01-22 14:42 +0000
    Re: Recognizers Alex <alex@rivadpm.com> - 2017-01-22 17:26 -0500
    Re: Recognizers Bernd Paysan <bernd@net2o.de> - 2017-01-24 00:57 +0000
      Re: Recognizers anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-01-24 16:23 +0000
        Re: Recognizers Bernd Paysan <bernd@net2o.de> - 2017-01-24 21:47 +0000
  Re: Recognizers Alex <alex@rivadpm.com> - 2017-01-23 08:30 -0500
    Re: Recognizers Alex <alex@rivadpm.com> - 2017-01-23 08:57 -0500
    Re: Recognizers Matthias Trute <matthias.trute@gmail.com> - 2017-01-23 10:58 -0800
      Re: Recognizers Alex <alex@rivadpm.com> - 2017-01-23 14:45 -0500
      Re: Recognizers JennyB <jennybrien@googlemail.com> - 2017-01-27 15:05 -0800
    Re: Recognizers Alex <alex@rivadpm.com> - 2017-01-29 22:54 +0000
      Re: Recognizers JennyB <jennybrien@googlemail.com> - 2017-01-30 09:11 -0800
      Re: Recognizers anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-01-30 16:34 +0000
  Re: Recognizers Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2017-01-31 21:03 +0000
    Re: Recognizers albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-02-01 12:37 +0100

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