Evaluating a String in Prolog

Question

In prolog I have a string that needs to be evaluated, for example:

X = '4+2/5'

Is there a way to convert or parse this string into an expression to be evaluated?

Something like:

?- String_Eval('4+2/5', Result).
Result = 4.4.

Using SWI-Prolog 6.6.6.

Thanks

Answer 1

You can use the predicate term_to_atom/2 to convert the atom (what you call a string) into an evaluable term, then use the is operator to perform the specified operation(s). Care should be taken if security is a concern as this roughly equivalent to an eval in JavaScript.

Full example

?- term_to_atom( T, '4 + 2 / 5' ).
T = 4+2/5.

?- term_to_atom( T, '4 + 2 / 5' ), X is T.
T = 4+2/5,
X = 4.4.