The ECMA Eiffel standard has
?T either a void reference or a reference to an instance of T
!T a reference to an instance of T
T same as !T in ECMA Eiffel; used to be same as ?T
similarly, C# "invented" Maybe and called it Nullable: http://msdn.microsoft.com/en-us/library/1t3y8s4s(VS.80).aspx NB: this is very good "propaganda" also in the sense that as a teacher you can say: if you learn Haskell now, with high probability you are learning things that will appear in following years' versions of C#/Java/whatever. Best regards, J.W.
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