Prolog calculator simply returns true - prolog

Question

I'm writing a calculator in Prolog that reads natural language questions and returns a number answer for a class assignment, and I'm nearly complete. However, when I input a sentence the program simply returns 'Yes' and then quits. As far as I can tell it doesn't even read in the sentence. This is my first time writing in Prolog, so I have no clue what is wrong. Any help would be greatly appreciated.
My code:
:- consult('aux.p').
accumulator(0).
start :-
write('Cranky Calculator'), nl,
write('-----------------'), nl,
cvt.
cvt :-
write('What do ya want?'), nl,
read_sentence(Question),
butlast(Question, Questio),
Questio \== [quit], !,
(
phrase(sentence(Value), Questio, []),
write(Value);
write_string('Stop it with your gibberish!')
), nl,
cvt.
cvt.
reset(V) :-
retract(accumulator(_)),
assert(accumulator(V)).
accumulate('plus', N, Value) :-
{Temp is accumulator(_)},
{Value is Temp + N},
reset(Value).
accumulate('minus', N, Value) :-
{Temp is accumulator(_)},
{Value is Temp - N},
reset(Value).
accumulate('divided', N, Value) :-
{Temp is accumulator(_)},
{Value is Temp / N},
reset(Value).
accumulate('times', N, Value) :-
{Temp is accumulator(_)},
{Value is Temp * N},
reset(Value).
accumulate(N1, 'plus', N2, Value) :-
{Value is N1 + N2},
reset(Value).
accumulate(N1, 'minus', N2, Value) :-
{Value is N1 - N2},
reset(Value).
accumulate(N1, 'divided', N2, Value) :-
{Value is N1 / N2},
reset(Value).
accumulate(N1, 'times', N2, Value) :-
{Value is N1 * N2},
reset(Value).
%------------------base productions---------------------
% sentence can be to an entirely new question or simply be an addition
% to the previous one
sentence(V) --> base(V1), {V is V1}.
sentence(V) --> additional(V1), {V is V1}.
sentence --> [].
base(Value) -->
pro, be, number(N1), oper(OP), number(N2), qmark,
{
accumulate(N1, OP, N2, V), {Value is V}
}.
additional(Value) -->
oper(OP), number(N), qmark,
{
accumulate(OP, N, V), {Value is V}
}.
pro --> [what].
pro --> [how], [much].
be --> [is].
number(N) --> five_digit(N1), {N is N1}.
five_digit(N) --> ten_thousands(V1), four_digit(V2), {N is 1000 * V1 + V2}.
four_digit(N) --> thousands(V1), three_digit(V2), {N is 1000 * V1 + V2}.
three_digit(N) --> hundreds(V1), two_digit(V2), {N is 100 * V1 + V2}.
two_digit(N) --> tens(V1), one_digit(V2), {N is V1 + V2}.
two_digit(N) --> teens(V), {N is V}.
one_digit(N) --> digit(V), {N is V}.
one_digit(0) --> [].
ten_thousands(T) --> tens(V), thousand, {T is V}.
ten_thousands(T) --> tens(V), {T is V}.
ten_thousands(T) --> teens(V), thousand, {T is V}.
ten_thousands(0) --> [].
thousands(T) --> digit(V), thousand, {T is V}.
thousands(0) --> [].
hundreds(T) --> digit(V), hundred, {T is V}.
hundreds(0) --> [].
thousand --> [thousand].
hundred --> [hundred].
digit(1) --> [one].
digit(2) --> [two].
digit(3) --> [three].
digit(4) --> [four].
digit(5) --> [five].
digit(6) --> [six].
digit(7) --> [seven].
digit(8) --> [eight].
digit(9) --> [nine].
tens(20) --> [twenty].
tens(30) --> [thirty].
tens(40) --> [fourty].
tens(50) --> [fifty].
tens(60) --> [sixty].
tens(70) --> [seventy].
tens(80) --> [eighty].
tens(90) --> [ninety].
teens(10) --> [ten].
teens(11) --> [eleven].
teens(12) --> [twelve].
teens(13) --> [thirteen].
teens(14) --> [fourteen].
teens(15) --> [fifteen].
teens(16) --> [sixteen].
teens(17) --> [seventeen].
teens(18) --> [eighteen].
teens(19) --> [nineteen].
oper(plus) --> [plus].
oper(plus) --> [and].
oper(minus) --> [minus].
oper(divided) --> ['divided by'].
oper(times) --> [times].
qmark --> ['?'].
The output I get looks like:
|: what is twelve plus two?
Yes

Answer 1

I took your code as a spec for a calculator that also gives the
result as text. The idea here is to combine DCG and CLP(FD).
CLP(FD) is constraint solving for finite domains. Finite domains
should be enough for your calculator. To enable CLP(FD) you have
first to load the appropriate library. In Jekejeke Minlog this
is done as follows:
:- ensure_loaded(library('clpfd.px')).
The code has first a section that can not only recognize numbers
but also generate text for numbers. This is mainly the part where
DCGs are combined with CLP(FD):
number(N) --> {N #= 1000 * V1 + 100 * V2 + V3}, thousands(V1),
hundreds(V2), two_digit_opt(V3).
thousands(N) --> two_digit(N), thousand.
thousands(0) --> [].
thousand --> [thousand].
hundreds(N) --> digit(N), hundred.
hundreds(0) --> [].
hundred --> [hundred].
two_digit_opt(N) --> two_digit(N).
two_digit_opt(0) --> [].
two_digit(N) --> {N #= V1*10 + V2}, tens(V1), digit_opt(V2).
two_digit(N) --> {N #= V+10}, teens(V).
two_digit(N) --> digit(N).
digit_opt(N) --> digit(N).
digit_opt(0) --> [].
digit(1) --> [one].
digit(2) --> [two].
digit(3) --> [three].
digit(4) --> [four].
digit(5) --> [five].
digit(6) --> [six].
digit(7) --> [seven].
digit(8) --> [eight].
digit(9) --> [nine].
tens(2) --> [twenty].
tens(3) --> [thirty].
tens(4) --> [fourty].
tens(5) --> [fifty].
tens(6) --> [sixty].
tens(7) --> [seventy].
tens(8) --> [eighty].
tens(9) --> [ninety].
teens(0) --> [ten].
teens(1) --> [eleven].
teens(2) --> [twelve].
teens(3) --> [thirteen].
teens(4) --> [fourteen].
teens(5) --> [fifteen].
teens(6) --> [sixteen].
teens(7) --> [seventeen].
teens(8) --> [eighteen].
teens(9) --> [nineteen].
Here is a prove that the bidirectionality works:
?- phrase(number(X),[fifty,five]).
X = 55 ;
No
?- phrase(number(55),X).
X = [fifty,five] ;
No
Adding the calculator was straight forward. I didn't use assert/retract,
I simply using an argument in an infinite loop. I don't know how healthy
this is for your Prolog system, especially since we now inbetween touch
the constraint store. At least in Jekejeke Minlog as of version 0.7.2
the constraint store will not yet be completely recycled, so that one
cannot run the loop indefinitely.
But to show how all the pieces can be put together, the loop solution
is fine. The code reads as follows:
loop(S) :-
write('> '),
flush_output,
read(L),
phrase(cmd(C),L),
do(C,S,T),
phrase(number(T),M),
write(M), nl,
!, loop(T).
loop(S) :-
write('?'), nl,
loop(S).
do(set(N),_,N).
do(add(N),S,T) :- T is S+N.
do(sub(N),S,T) :- T is S-N.
cmd(set(N)) --> factor(N).
cmd(add(N)) --> [plus], factor(N).
cmd(sub(N)) --> [minus], factor(N).
factor(M) --> number(N), more(N, M).
more(N, M) --> [times], number(H), {J is N*H}, more(J,M).
more(N, M) --> [divided, by], number(H), {J is N//H}, more(J,M).
more(N, N) --> [].
And here is an example execution:
?- loop(0).
> [eleven,times,eleven].
[one,hundred,twenty,one]
> [minus,sixty,six].
[fifty,five]
Here is a little how to for the Jekejeke CLP(FD)
Jekejeke Minlog Desktop Installation
https://www.youtube.com/watch?v=6ZipaIrxSFQ
Jekejeke Minlog Android Installation
https://www.youtube.com/watch?v=Y2P7cEuOIws