[PD] how to set variable types

[AshK]

Hi list,

I couldn't find it in the doc.
I have an abstraction with 2 arguments : [abstraction 1 2], inside the 
abstraction I send $1 to [print] and it returns 1. That's perfect but 
instead of the [print] I want a number box. When I try nothing happens.
How can I get my variable in a number box?

thanks