building a list with Recursion with Prolog -


i have recursive predicate builds list it's suposed to, problem starts 'debuilding it' , gives me empty list, linha predicate ok, gives value vel, , or. 

actualizarveiculos(_,[],d).  actualizarveiculos(tempo,[(x,y)|restoveiculos],novaveiculos):-     linha(y,or,vel),     faz_andar_veic(or,(x,y),c,mod(tempo,vel)),     append(novaveiculos,[c],d),     actualizarveiculos(tempo,restoveiculos,d).  faz_andar_veic(90,(x,y),(x+1,y),0).  faz_andar_veic(270,(x,y),(x-1,y),0).  faz_andar_veic(_,(x,y),(x,y),c):-   c=\=0.

the trace

you need change follows:

actualizarveiculos(_,[],d, d).  actualizarveiculos(tempo,[(x,y)|restoveiculos],acc, res):-     or 2,     vel 2,     faz_andar_veic(or,(x,y),c,mod(tempo,vel)),     append(acc,[c],d),     actualizarveiculos(tempo,restoveiculos,d, res).  faz_andar_veic(90,(x,y),(x+1,y),0).  faz_andar_veic(270,(x,y),(x-1,y),0).  faz_andar_veic(_,(x,y),(x,y),c):-     c=\=0.

test run:

[debug]  ?- actualizarveiculos(5, [(-5,3), (-4,4), (-4,5)], [], res). res = [ (-5, 3), (-4, 4), (-4, 5)] .

in trace provided query actualizarveiculos(5, [(-5,3), (-4,4), (-4,5)], n). since n unbound novaveiculos becomes unbound , do: append(novaveiculos,[c],d), not think or atleast intended do. tries append unbound variable list , result unified unbound variable can give infinite number of solutions, e.g.:

[debug]  ?- actualizarveiculos(5, [(-5,3), (-4,4), (-4,5)], n). n = [] ; n = [_g3430] ; n = [_g3430, _g3436] ; n = [_g3430, _g3436, _g3442] ; n = [_g3430, _g3436, _g3442, _g3448] ; n = [_g3430, _g3436, _g3442, _g3448, _g3454] ; n = [_g3430, _g3436, _g3442, _g3448, _g3454, _g3460] ; n = [_g3430, _g3436, _g3442, _g3448, _g3454, _g3460, _g3466] ; n = [_g3430, _g3436, _g3442, _g3448, _g3454, _g3460, _g3466, _g3472] ; n = [_g3430, _g3436, _g3442, _g3448, _g3454, _g3460, _g3466, _g3472, _g3478] ; n = [_g3430, _g3436, _g3442, _g3448, _g3454, _g3460, _g3466, _g3472, _g3478|...] ;

hope helps, comment if have questions. since didn't provide linha/3 predicate exchanged 2 unifications:

or 2, vel 2,

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