There's the following alternative. mike data TermOp = TermAnd | TermOr deriving (Show, Eq) data Term = Not Term | Op Term TermOp Term | Literal Char deriving Show assoc (Op (Op t1 op1_2 t2) op12_3 t3) | op1_2 == op12_3 = Op t1 op1_2 (Op t2 op1_2 t3) assoc t = t (&&&) = (`Op` TermAnd) (|||) = (`Op` TermOr) tlA = Literal 'A' tlB = Literal 'B' tlC = Literal 'B' tt1 = Not tlA &&& tlB -- Should not assoc. tt2 = tt1 &&& tlC -- Should assoc. tt3 = tt1 ||| tlC -- Should not assoc. tests = putStr $ unlines $ map (show . (\t -> (t, assoc t))) [tt1, tt2, tt3]

Hello! My question concerns a general term datatype: data Term = Not Term | Term :&&: Term | Term :||: Term | Literal Char

Is it somehow possible to write a generic function that applies the associativity rules on a "Term" (by using pattern matching) and works with both data constructors or is it necessary to write one for :&&: and :||: ?

Something like: assoc :: Term -> Term assoc ((t1 `op` t2) `op` t3) = .... -- this doesn't work