On Aug 31, 2010, at 12:03 PM, michael rice wrote:
I tried creating an instance earlier but
*Main> :t (->) Int Char
<interactive>:1:1: parse error on input `->'
Try:
Prelude> :info (->)
data (->) a b -- Defined in GHC.Prim
If you want type-information about values, use :t. If you want
information about types (and the "type-level language"), use :info.
This includes stuff like class definitions and instances in scope.
For example, if I include Control.Monad:
Prelude Control.Monad.Instances> :info (->)
data (->) a b -- Defined in GHC.Prim
instance Monad ((->) r) -- Defined in Control.Monad.Instances
instance Functor ((->) r) -- Defined in Control.Monad.Instances
:info is pretty cool:
Prelude Control.Monad.Instances> :info Monad
class Monad m where
(>>=) :: m a -> (a -> m b) -> m b
(>>) :: m a -> m b -> m b
return :: a -> m a
fail :: String -> m a
-- Defined in GHC.Base
instance Monad ((->) r) -- Defined in Control.Monad.Instances
instance Monad Maybe -- Defined in Data.Maybe
instance Monad [] -- Defined in GHC.Base
instance Monad IO -- Defined in GHC.Base
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