[Haskell-cafe] Haskell Propeganda

Richard A. O'Keefe ok at cs.otago.ac.nz
Wed Aug 27 21:46:41 EDT 2008

On 28 Aug 2008, at 8:34 am, Aaron Tomb wrote:
> What type safety buys you, in my mind, is that Nothing is only a  
> valid value for explicit Maybe types. In cases where you don't use  
> Maybe, the "null" situation just can't occur. In languages with null  
> pointers, any pointer could possibly be null.

This is not true of Eiffel.
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

I suppose you could call the detachable type ?T an *implicit* Maybe.
Needless to say, the switch in semantics of undecorated T helped to
fork the Eiffel community...

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