Hello all! If I try to write, for example: instance Alternative MyData where empty = NoMyData a <|> b = if a == b then ... I get error (see on bottom of the mail) sure, bcz I suppose something like: Eq a => (MyData a) All my attempts to add something to instance's `pure` signature have failed. How can I instantiate something with additional restrictions, like in this case? Or are there another solutions for such problem? Interesting is that MyData derives Eq itself! Which, I suppose, must means that "Eq (MyData a)", and if it's true than "Eq a" is true, because how "MyData a" can be Eq without to be "Eq a" (with *automatically deriving* of Eq instance) ?! By the way, for Monoid (which is "* -> Constraint") I can add "Eq a" constraint without problems: instance Eq a => Monoid (Origin a) where mempty = NoMyData mappend NoMyData a = a mappend a NoMyData = a mappend (MyData a) (MyData b)|a == b = MyData a |otherwise = NoMyData but not for Alternative, which is "(* -> *) -> Constraint". *ORIGINAL ERROR DUMP*: ====================== 42 16 error error: • No instance for (Eq a) arising from a use of ‘==’ Possible fix: add (Eq a) to the context of the type signature for: (<|>) :: Origin a -> Origin a -> Origin a • In the expression: a == b In the expression: if a == b then NoOrigin else NoOrigin In an equation for ‘<|>’: a <|> b = if a == b then NoOrigin else NoOrigin (intero) /Best regards Paul