[Haskell-cafe] Writing guards shorthand

[Joel Reymont]

Support I want to infer the type given an Op that looks like this  
(incomplete):

data Op
     = Minus
     | Plus
     | Mul
     | LT
     | GT

Is there a shorthand way of bunching Minus, Plus and Mul in a  
function guard since they all result in TyNum whereas the rest in  
TyBool?

I really don't want several function clauses and neither do I want  
separate guards for every constructor.

	Thanks, Joel

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