Defines Language, which is the required constraint on expressions that are to be represented in e-graph and on which equality saturation can be run.

Example

data Expr a = Sym String
            | Const Double
            | UnOp  UOp a
            | BinOp BOp a a
            deriving ( Eq, Ord, Functor
                     , Foldable, Traversable)

instance Eq1 Expr  where
    ...
instance Ord1 Expr where
    ...

instance Analysis Expr where
    ...

-- meaning we satisfy all other constraints and Expr is! a language
instance Language Expr