Jon Fairbairn wrote :

Hi, I am trying to create an overloaded function "à la Java" to be able to call it either with a string or a number. Ex : definePort "http" definePort 80 but I have problem with restrictions in Haskell's type system

Is there a better solution ?

If we knew /why/ you wanted to do this we might be able to help. I can't see why you want to allow Strings, which have far too wide a range of values, as arguments to something that takes a port designator as an argument. data Port = Tcpmux | Nbp | Echo_ddp | Rje | Zip | Echo_tcp | ... deriving Enum, ... instance Num Port where ... would seem like a better way to me. Jón I am trying to build a functional firewall generator. The first part describes the available protections (kernel, anti-address spoofing, etc.). The second desribes every protocol, and the necessary rules if the corresponding service is enabled (e.g. open the http port...). In the third one, the user will choose the services he wants to use/open and the static parameters (for instance the squid port number). I wanted the user part to be "user-friendly", even if it is an Haskell program. So the commands definePort "squidPort" 3128 Seemed more logical than definePort "squidPort" "3128" The problem is that the numeric literal 3128 is considered as being a member of Num class, and not as beeing an Int. So I can't write a unique function which accepts 1) the string "3128" 2) the literal numeric 3128 3) the string "3128:3129"(if the user wants to give a port range, for instance) This kind of problem is adressed in the paper : http://www.cse.ogi.edu/~mbs/pub/overloading/ where the "closed" class extension seems to solve this kind of ambiguous type difficulty. But it does not seem to have been implemented yet Alain