On Fri, Aug 12, 2011 at 18:52, Patrick Browne <[email protected]> wrote:
> Why does the Haskell :type command only sometimes print the type-class? > Haskell infers the most specific type applicable. If the most specific it can get is a typeclass, that's what it produces; if it can infer an explicit type, it will. > Should I expect type-class inference as well as type inference? > Maybe the type-class is inferred where possible, but not always printed? > Typeclasses are not independent of types, and are not inferred separately from types. If you want to know what typeclasses a type is a member of, use :info. Haskell supports polymorphism: a bound expression does not need to have a single specific type, it can apply to multiple types and adapt itself to the type at its use site. Typeclasses are part of how this is accomplished. So if a bound expression is polymorphic, you will see its type expressed in terms of type variables, possibly with typeclass contexts. -- brandon s allbery [email protected] wandering unix systems administrator (available) (412) 475-9364 vm/sms
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