[Haskell-cafe] do we have something like isDefined or isNull in Haskell?

[Vladimir Portnykh]

Suppose there is a data definition in Haskell:
data MyType = MyType { date	:: Double,
		   weight 	:: Double,
		  height	:: Double
		} deriving (Eq, Ord, Show)

Is it possible to check if the field height, for example, is filled 
in(defined)? Can we give default values in Haskell?

Many thanks and sorry fro so sily questions. Vladimir

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