Prolog findall help

Question

So i have a database of train stations simply labelled train(st1, st4). etc

I want to implement a find all predicate so that a user could query allpaths(X,Y, Paths). And the code would return all paths from X to Y.

Any help would be awesome thanks

Is this a homework question? Do you have a predicate for a single path "path(X, Y, Path)"? — Little Bobby Tables, Nov 27 '10 at 13:53
Possible duplicate of [Prolog findall/3](http://stackoverflow.com/questions/21082855/prolog-findall-3) — , Oct 12 '15 at 11:52

sowa · Accepted Answer · 2010-11-27T16:07:46.990

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train(st1,st4).
train(st1,st2).
train(st2,st3).
train(st3,st4).
train(st4,st5).
train(st3,st6).
train(st6,st5).
find(X,Y,[X|Y]):-train(X,Y).
find(X,Y,[X|Q]):-train(X,Z),find(Z,Y,Q).
findall2(X,Y):-find(X,Y,Q),write(Q),nl,fail.

I hope it's what you were looking for.

edited Nov 27 '10 at 16:07

answered Nov 27 '10 at 15:47

sowa

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score 0 · Answer 2 · answered Nov 27 '10 at 17:27

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Same answer as @sowa, but with the last line changed to:

allpaths(X, Y, Ps) :- findall(P, find(X, Y, P), Ps).

findall/3 is a built-in Prolog predicate.

answered Nov 27 '10 at 17:27

Little Bobby Tables

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Prolog findall help

2 Answers2