On Wed, Nov 26, 2014, at 01:17 PM, Wojtek Narczyński wrote:
dk.hs:9:17: Expected a type, but ‘cmd’ has kind ‘CmdKind’ In the type ‘cmd -> ByteString’ In the class declaration for ‘Serialize’
The error message says that it expected a type. That might be a bit confusing. What it means by "type" is "a thing with kind *". That is the kind of types, and those types are the only things which have values. The argument to a function must be a value, so the argument to the "->" operator must be a type. Another example to consider which might make this more clear: Prelude> let { f :: Maybe -> a; f x = undefined } <interactive>:2:12: Expecting one more argument to ‘Maybe’ Expected a type, but ‘Maybe’ has kind ‘* -> *’ In the type signature for ‘f’: f :: Maybe -> a Notice that in the type signature for f, I forgot to apply Maybe to an argument. On its own, Maybe has kind * -> *, which means that Maybe is not a type. After all, there is no such thing as a "value of type Maybe".
Is this so by design, or should I write it in a different way, or is it just not implemented?
I don't think it's clear what you are trying to do, so it is hard to say what you should write. -Karl