[Haskell] Classes with no data type

Thomas Davie tatd2 at kent.ac.uk
Mon Oct 9 19:23:32 EDT 2006

   I've met an interesting problem in terms of how to type a data  
structure and the functions that operate upon it.

The problem centres around a single data type.  This data type can be  
constructed in multiple ways using different functions, depending on  
the options the user specifies.  That's all simple enough.  The  
problem really comes later on.  Depending on the function used  
generate the data structure I want to use different functions later  
on for example, to display the data.

Thus I have a typical classes problem, in that I have several  
implementations of essentially the same function for different  
circumstances.  The problem is, they must all operate on the same  
data type, so I cannot define them as seperate instances.

Anyone got any ideas how to type this?


More information about the Haskell mailing list