Sandbox restriction when using call/1 on is/2 in Swish


On, when I have

sum(X1, X2, S):-S is X1 + X2.

and try

?-clause(sum(2,3,X), B), call(B).

I get the error

Sandbox restriction! Could not derive which predicate may be called from call(C).

Is there any way around this? I have a meta interpreter that should yield info about arithmetical computations.