# Converting between boxed and unboxed types

**Keith Wansbrough
**
Keith.Wansbrough@cl.cam.ac.uk

*Tue, 12 Mar 2002 11:23:13 +0000*

>* I would like to print an unboxed value to the screen. But to use "show" on
*>* a type it has to be boxed. How do I rebox an unboxed type? Sorry if the
*>* answer to this is obvious - I have spent quite some time looking for the
*>* solution.
*
You need to know what kind of box - the unboxed value no longer has the `tag' saying what type it is.
Boxed Ints, for example, are declared like this in the prelude:
data Int = I# Int#
So to build an Int from an Int#, simply say (I# x), like this:
case (+# 1# 42#) of {
x -> show (I# x)
}
(you'll probably need to import whichever module has the definition of Int in it).
Hope this helps..
--KW 8-)
--
Keith Wansbrough <kw217@cl.cam.ac.uk>
http://www.cl.cam.ac.uk/users/kw217/
University of Cambridge Computer Laboratory.