6 May
2010
6 May
'10
3:56 a.m.
On Wed, May 05, 2010 at 02:54:27PM -0700, Ryan Ingram wrote:
ErrorT is just a newtype wrapper, changing the order/application of the type variables.
newtype ErrorT e m a = ErrorT (m (Either e a)) runErrorT (ErrorT action) = action
This gives the bijection:
ErrorT :: m (Either e a) -> ErrorT e m a runErrorT :: ErrorT e m a -> m (Either e a)
That syntax is not clear for me - so ErrorT is some sort of function (calculation), which takes a monad with type (Either e a) and produces type ErrorT e m a ? Basically, i don't understand what does "ErrorT ::" means - it should name the function - but it starts with capital letter? I feel like I missed something when learning type system and syntax of Haskell :( -- Eugene N Dzhurinsky