I think of (r -> m a) as a type signature and Int or Bool by themselves as types. So, all type signatures are themselves types?
Michael
--- On Wed, 12/29/10, Henning Thielemann <lemming@henning-thielemann.de> wrote:
From: Henning Thielemann <lemming@henning-thielemann.de>
Subject: Re: [Haskell-cafe] Reader monad
To: "michael rice" <nowgate@yahoo.com>
Cc: haskell-cafe@haskell.org
Date: Wednesday, December 29, 2010, 12:28 PM
On Wed, 29 Dec 2010, michael rice wrote:
> In the case of ReaderT and StateT
>
> newtype ReaderT r m a = ReaderT {
> -- | The underlying computation, as a function of the
environment.
> runReaderT :: r -> m a
> }
>
> newtype StateT s m a = StateT { runStateT :: s -> m (a, s) }
>
> what is the existing type?
The existing type is 'r -> m a'. You could also write
> newtype ReaderT r m a = ReaderT (r -> m a)
This would be the same type as above, but it would have no accessor function 'runReaderT'.
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