Definition of a path/trail/walk

Question

Many predicates define some kind of an acyclic path built from edges defined via a binary relation, quite similarly to defining transitive closure. A generic definition is t

Answer 1

I want to focus on naming the predicate.

• Unlike maplist/2, the argument order isn't of primary importance here.

• The predicate name should make the meaning of the respective arguments clear.

So far, I like path_from_to_edges best, but it has its pros and cons, too.

path_from_to_edges(Path,From,To,Edges_2) :-
    path(Edges_2,Path,From,To).

Let's pick it apart:

• pro: path is a noun, it cannot be mis-read a verb. To me, a list of vertices is implied.

• pro: from stands for a vertex, and so does to.

• con: edges is somewhat vague, but using lambdas here is the most versatile choice.

• con: According to Wikipedia, a path is a trail in which all vertices (except possibly the first and last) are distinct. So that would need to be clarified in the description.

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Using lambdas for a lists of neighbor vertices Ess:

?- Ess  = [a-[b],b-[c,a]], 
   From = a,
   path_from_to_edges(Path,From,To,\X^Y^(member(X-X_neibs,Ess),member(Y,X_neibs))).
Ess = [a-[b],b-[c,a]], From = a, To = a, Path = [a]     ;
Ess = [a-[b],b-[c,a]], From = a, To = b, Path = [a,b]   ;
Ess = [a-[b],b-[c,a]], From = a, To = c, Path = [a,b,c] ;
false.

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Edit 2015-06-02

Another shot at better naming! This leans more on the side of maplist/2...

graph_path_from_to(P_2,Path,From,To) :-
   path(P_2,Path,From,To).

Here, graph, of course, is a noun, not a verb.

Regarding the meaning of "path": paths definitely should allow From=To and not exclude that by default (with pairwise term inequalities). It is easy to exclude this with an additional dif(From,To) goal, but not the other way round.