This question is directly related to first order logic creating terms for arithmetic expressions using prolog. After implementing the logic as per the link I have issues with the formatting of the ourput for printauth/1
. It currently results as 8-2+4* -3
, how is it possible to get something like ((8-2)+(4* -3))
(notice its not the same as +(-(8,2),*(4,-3)))
.
I have been trying to using various options (\k,\q) in format/2
predicate but nothing works. even I tried write_canonical
and other write predicates, still no success.
printterm(Term) :- arithmetic_expression(Term, Expr), format("(~q)\n", [Expr]).
%write_canonical(Expr).
%write_term(Expr, [ignore_ops(true)]).
%format("(~q)\n", [Expr]) .
current output:
?- printterm(plus((minus(8,2)),(times(4,3)))).
(8-2+4*3)
true .
expected output:
?- printterm(plus((minus(8,2)),(times(4,3)))).
((8-2)+(4*3))
true .
Is it possible to achieve this?
The term you passed to your printterm
:
plus((minus(8,2)),(times(4,3)))
This is conventionally written as:
plus(minus(8, 2), times(4, 3))
The parentheses are not needed and are indeed lost when the term is read. Try:
?- X = plus((minus(8,2)),(times(4,3))).
To get what you want it seems you really need to program it. For example:
print_arithmetic_expression(E) :-
phrase(parenthesized_expression(E), P),
format("~s~n", [P]).
parenthesized_expression(E) -->
atomic_expr(E),
!.
parenthesized_expression(E) -->
{ expr_op(E, Op, A, B) },
pexp(A),
" ", [Op], " ",
pexp(B).
atomic_expr(E) -->
{ atomic(E),
format(codes(C), "~w", [E])
},
C.
expr_op(plus(A,B), 0'+, A, B).
expr_op(minus(A,B), 0'-, A, B).
expr_op(times(A,B), 0'*, A, B).
pexp(E) -->
atomic_expr(E),
!.
pexp(E) -->
{ expr_op(E, Op, A, B) },
"(",
pexp(A),
" ", [Op], " ",
pexp(B),
")".
I get:
?- print_arithmetic_expression(plus(minus(8, 2), times(4, 3))).
(8 - 2) + (4 * 3)
true.