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Re: Reifying backtracking for Haskell programmers

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But what does it do?

A step goes through the Byrd Box, just like a Prolog debugger:

The Byrd Box Model And Ports
models each predicate in a Prolog program as a
state machine (“box”) that transitions through
states (“ports”) as a program is evaluated.
https://www.swi-prolog.org/pldoc/man?section=byrd-box-model

Mild Shock schrieb:
> 
> Does it work?
> 
> t assumes the rules and facts in a predicate rule/2, here an example:
> 
> % rule(-Term, -List)
> :- dynamic rule/2.
> rule(app([], X, X), []).
> rule(app([X|Y], Z, [X|T]), [app(Y, Z, T)]).
> 
> rule(rev([], []), []).
> rule(rev([X|Y], Z), [rev(Y,T),app(T,[X],Z)]).
> Works fine:
> 
> ?- run(true, [app(X,Y,[1,2,3]),write(('X'=X,'Y'=Y)),nl,fail], []).
> X=[],Y=[1,2,3]
> X=[1],Y=[2,3]
> X=[1,2],Y=[3]
> X=[1,2,3],Y=[]
> false.
> 
> ?- run(true, [rev([1,2,3],X),write('X'=X),nl,fail], []).
> X=[3,2,1]
> false.
> 
> Mild Shock schrieb:
>> One buzzword that Markus Triska is using is:
>>
>> Reifying backtracking
>> https://www.metalevel.at/acomip/
>>
>> But he is more up to meta interpreters.
>>
>> Can we turn the whole thing into something small step?
>>
>> Here is a take:
>>
>> % step(+Bool, +List, +List, -Bool, -List, -List)
>> step(true, [write(Term)|Cont], CPs, true, Cont, CPs) :- !, write(Term).
>> step(true, [nl|Cont], CPs, true, Cont, CPs) :- !, nl.
>> step(true, [Goal|Cont], CPs, Flag, Cont2, CPs2) :-
>>     findall(Goal-Body, rule(Goal, Body), Pairs),
>>     pick(Pairs, [Goal|Cont], CPs, Flag, Cont2, CPs2).
>> step(fail, _, [Pairs-Cont|CPs], Flag, Cont2, CPs2) :-
>>     pick(Pairs, Cont, CPs, Flag, Cont2, CPs2).
>>
>> % pick(+Bool, +List, +List, -Bool, -List, -List)
>> pick([], Cont, CPs, fail, Cont, CPs).
>> pick([Goal-Body|Pairs], Cont, CPs, true, Cont3, [Pairs-Cont|CPs]) :-
>>     copy_term(Cont, [Goal|Cont2]),
>>     append(Body, Cont2, Cont3).
>>
>> % run(+Bool, +List, +List)
>> run(Flag, Cont, CPs) :-
>>     step(Flag, Cont, CPs, Flag2, Cont2, CPs2),
>>     run(Flag2, Cont2, CPs2).
>>
>> It only carries around a state consisting of flag for CALL
>> or REDO, and the continuations and the choicepoints. The meaning
>> of the transformed flag is EXIT or FAIL.
> 

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Reifying backtracking for Haskell programmers Mild Shock <janburse@fastmail.fm> - 2024-02-26 01:37 +0100
  Re: Reifying backtracking for Haskell programmers Mild Shock <janburse@fastmail.fm> - 2024-02-26 01:38 +0100
    Re: Reifying backtracking for Haskell programmers Mild Shock <janburse@fastmail.fm> - 2024-02-26 01:39 +0100

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