Transition Issue Unknown Cause

Question

I am trying to create a NFA to describe it with states which accepts "y|x*"

This is what I have tried so far:

acpt(State, [A]).
acpt(State, []) :- acpt(State).
acpt(State, InputList) :- InputList = [A],
                             transition(State, X).

When given the input

acpt(q0, [x,y]).

I'm looking for it to return t

true

When given

acpt(q0, [x,x,y]).

it should return

false

The code I have produces a few errors and I was wondering if I can get some help. Thx.

Answer 1

I comment the corrections required to get

1 ?- acpt(q0, [x,y]).
true 
.

2 ?- acpt(q0, [x,x,y]).
false.

working code:

% totally useless:
% acpt(State, [A|B]).

% typo: of course, we need acptng/1
% acpt(State, []) :- acpt(State).

acpt(State, []) :- acptng(State).
acpt(State, [A|B]) :-
    transition(State, X, A),
    acpt(X, B).

now, apart the test input being working, I must say that I cannot see the 'epsilon rule' implementation. IIRC, a NFA should allows to change state without consuming input.

edit

a trace

4 ?- leash(-all),trace,acpt(q0, [x,x,x]).
   Call: (7) so:acpt(q0, [x, x, x])
   Call: (8) so:transition(q0, _G1431, x)
   Exit: (8) so:transition(q0, q3, x)
   Call: (8) so:acpt(q3, [x, x])
   Call: (9) so:transition(q3, _G1431, x)
   Exit: (9) so:transition(q3, q3, x)
   Call: (9) so:acpt(q3, [x])
   Call: (10) so:transition(q3, _G1431, x)
   Exit: (10) so:transition(q3, q3, x)
   Call: (10) so:acpt(q3, [])
   Call: (11) so:acptng(q3)
   Exit: (11) so:acptng(q3)
   Exit: (10) so:acpt(q3, [])
   Exit: (9) so:acpt(q3, [x])
   Exit: (8) so:acpt(q3, [x, x])
   Exit: (7) so:acpt(q0, [x, x, x])
true 
.