Question

So, following along with a sample code on streams, this fails to be loaded into ghci:

data MyStream a = MyStream a (MyStream a)

intsFrom n :: MyStream Integer
intsFrom n = MyStream n $ intsFrom $ n + 1

Getting error:

stream.hs:3:1:
    Invalid type signature: intsFrom n :: MyStream Integer
    Should be of form <variable> :: <type>
Failed, modules loaded: none.

Any ideas? Thanks!

Update: If I just type intsFrom :: MyStream Integer I get error:

stream.hs:4:1:
    The equation(s) for `intsFrom' have one argument,
    but its type `MyStream Integer' has none
Failed, modules loaded: none.

Answer 1

It looks like you want your signature to be something like this:

intsFrom :: Integer -> MyStream Integer

Integer here is your argument, and MyStream Integer is the result of intsFrom.