Prolog- translating English to C

Question

We have a relatively simple assignment that I understand in theory but I think I just don\'t quite understand Prolog\'s syntax enough to get that into code. Basically, we have a

Answer 1

If there is a reasonable small number of patterns, you could do:

english2C([add,X,to,Y], R) :- R is X+Y.
english2C([add,A,to,B,',',then,subtract,C], R) :- R is A+B-C.

edit

Those rules above compute the value. To translate, we can use DCG for matching, it's working 'backwards' as well.

english2C(In, R) :- phrase(toe(R), In, []).

toe(X+Y) --> [add,X,to,Y].
toe(X*Y) --> [multiply,X,by,Y].
toe(L-R) --> toe(L), [',',then,subtract,R].

test:

?- english2C(X,3+6).
X = [add, 3, to, 6].

edit sorry, I forgot a cut. With that added, I get

?- english2C([add,3,to,5,',',then,subtract,4],X).
X = 3+5-4.

?- english2C(L,3+5-4).
L = [add, 3, to, 5, ',', then, subtract, 4].

without, there is the loop after ;

?- english2C([add,3,to,5,',',then,subtract,4],X).
X = 3+5-4 ;
^CAction (h for help) ? goals
[698,875] toe(_G2096630, [add, 3, to, 5, ',', then, subtract, 4], _G2096652)
[698,874] toe('', '', _G2096652)
...

It's a single point change: do you prefer to find it yourself?