On 02/08/10 15:14, Tom Davies wrote:
I find it convenient sometimes to convert a Maybe value to an Either thus (excuse the syntax, it's CAL, not Haskell):
maybeToEither :: a -> Maybe b -> Either a b; maybeToEither errorValue = maybe (Left errorValue) (\x -> Right x);
but that seemingly obvious function isn't in Hoogle, AFAICT, so perhaps there's some other approach?
I just uploaded djinn-th [1], a fork of Lennart Augustsson's djinn [2] which uses TemplateHaskell to do things like: {-# LANGUAGE TemplateHaskell, ScopedTypeVariables #-} import Language.Haskell.Djinn (djinnD) $(djinnD "maybeToEither" [t|forall a b . a -> Maybe b -> Either a b|]) main = print . map (maybeToEither "foo") $ [Nothing, Just "bar"] and get some results, if not always the one you intended. [1] http://hackage.haskell.org/package/djinn-th [2] http://hackage.haskell.org/package/djinn Thanks, Claude -- http://claudiusmaximus.goto10.org