Apologies - sent too soon - code edited below

Dear All,

I am having problems writing a polymorphic function.

I have a type that has two constructors:

data Arg = IndArg {evi::Evi, t1::Treatment, t2::Treatment, out::Outcome, dir::Direction}

            | MetaArg {target::EviType}

            deriving (Show)

I have a function checks for conflict:

checkConflict :: Arg -> Arg -> Bool

checkConflict a b = if t1 a == t1 b && t2 a == t2 b && dir a /= dir b then True

                     else False

However, I can't make this work with both types of Argument - if I pass it MetaArg, it raises an error.

In another language, I would write something like:

checkConflict(ArgA,ArgB):

         if type(ArgA) == IndArg:

                  <do this>

         elif type(ArgA) == MetaArg:

                  <do other>

Any thoughts would be welcomed.

BW,

Matt

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