[racket] [racket-users]Is Racklog suitable to learn Prolog? A simple example just fails.

Racklog should have generated a stream of solutions here. That's my problem with it. -- Matthias





On Jul 4, 2014, at 5:37 AM, Scott Moore wrote:

> I'm not sure what behavior you were expecting for this program. Under standard prolog semantics (goal-directed) this program will yield infinitely many solutions, so this may not be a bug in racklog but rather in the program.
> 
> That said, Matthias is probably right that using a currently maintained package is probably a good idea.
> 
> Cheers,
> Scott
> 
> 
> On Thu, Jul 3, 2014 at 7:46 PM, WarGrey Gyoudmon Ju <juzhenliang at gmail.com> wrote:
> Okay, Thank you.
> 
> 
> On Fri, Jul 4, 2014 at 1:21 AM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
> 
> Yes, I corrected your program and ran into this bug. 
> 
> Try to use Kanren instead of Racklog. It isn't completely a legacy package but I doubt we can get a quick fix here. 
> 
> -- Matthias
> 
> 
> 
> 
> On Jul 3, 2014, at 4:53 PM, WarGrey Gyoudmon Ju wrote:
> 
>> Sorry, my example is not correct.
>> But this one still does not work:
>> 
>> #lang at-exp racket
>> 
>> (require racklog)
>> 
>> (define %edge
>>   (%rel ()
>>     [('a 'b)]
>>     [('b 'c)]
>>     [('c 'd)]
>>     [('d 'a)]))
>> 
>> (define %path
>>   (%rel (X Y Z)
>>     [(X Y) (%edge X Y)]
>>     [(X Y) (%edge X Z) (%path Z Y)]))
>> 
>> (let answer ([r (%which (X Y) (%path X Y))])
>>   (printf "~a --> ~a~n" (cdar r) (cdadr r))
>>   (answer (%more)))
>> 
>> This version also will not terminate.
>> 
>> On Thu, Jul 3, 2014 at 9:04 PM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
>> 
>> If you want to learn Prolog, why not use a free Prolog implementation?
>> 
>> Simply speaking, Modern Prolog seems to cut the illumos-based SunOS off, I cannot build it without headache and they does not answer me about this issue.
>> So I wander if Racklog is a legacy package?
>>  
>> 
>> If you want to learn about relational programming, use miniKanren, which is available of cKanren. Then you can also get to constraints. Maintainer cc-ed.
>> 
>> -- Matthias
>> 
>> 
>> 
>> On Jul 3, 2014, at 6:48 AM, WarGrey Gyoudmon Ju wrote:
>> 
>> > This example is rewritten from the datalog version.
>> >
>> > #lang racket
>> >
>> > (require racklog)
>> >
>> > (define %edge
>> >   (%rel ()
>> >     [('a 'b)]
>> >     [('b 'c)]
>> >     [('c 'd)]
>> >     [('d 'a)]))
>> >
>> > (define %path
>> >   (%rel (X Y)
>> >     [(X Y) (%edge X Y)]
>> >     [(X Y) (%edge X 'Z)
>> >              (%path 'Z Y)]))
>> >
>> > (%find-all (X Y) (%path X Y))
>> >
>> > It only gives four results.
>> >
>> > #lang racklog
>> >
>> > edge(a, b).
>> > edge(b, c).
>> > edge(c, d).
>> > edge(d, a).
>> >
>> > path(X, Y) :- edge(X, Y).
>> > path(X, Y) :- edge(X, Z), path(Z, Y).
>> >
>> > path(X, Y)?
>> >
>> > and this version will not terminate.
>> >
>> > Thanks in advance.
>> > ____________________
>> >  Racket Users list:
>> >  http://lists.racket-lang.org/users
>> 
>> 
> 
> 
> 
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