Find the type of object on the top of the stack
int SLang_peek_at_stack (void)
The SLang_peek_at_stack function is useful for determining the
data type of the object at the top of the stack. It returns the
data type, or -1 upon a stack-underflow error. It does not remove
anything from the stack.
SLang_pop_string, SLang_pop_integer