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

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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>>>
>>>
>>
>>
>
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