[Haskell-beginners] A Quantity Type - Integer without the Negative #'s

[Daniel Carrera]

Magnus Therning wrote:
> aditya siram wrote:
>> Hi all,
>> Is there a datatype in Haskell that can be used to represent only 
>> quantities >= 0?  I got bitten by a bug because I forgot to reject an 
>> amount that was below zero after applying a decrementing operator. A 
>> simple unit test would have caught this, but I was wondering if there 
>> was some way of getting the type system to ensure this.
> 
> Maybe Word32 (or one of it's siblings) would do?  It's basically the 
> same as 'unsigned int' in C, so it can under- and over-flow.

What's under-flow?