[Haskell-cafe] "Least common supertype"?

Richard O'Keefe ok at cs.otago.ac.nz
Wed Nov 11 17:57:39 EST 2009

On Nov 12, 2009, at 9:24 AM, Sean Leather wrote:

> Is there a name for the following concept?
[Generalising from
	(Int, Char) -> (Char, Int)
	(Char, Int) -> (Int, Char)
  to	(x,    y  ) -> (y,   x   )]

It's the "least specific generalisation", also known as anti- 
(Because unification finds the most general specialisation.)
As far as I know, it originated in this paper:
Gordon D. Plotkin. A Note on Inductive Generalization. In B. Meltzer  
and D. Michie, editors, Machine Intelligence, volume 5, pages 153-163.  
Elsevier North-Holland, New York, 1970.

More precisely, with the type constraints, it's sorted anti-unification.

might be worth a look.

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