Least Common Generalization. Cheers, Thu
2009/11/11 Eugene Kirpichov <ekirpic...@gmail.com>: > Is the name of the concept.... "Most general unifier" (MGU) ? (See: > Hindley-Milner type inference) > > 2009/11/11 Sean Leather <leat...@cs.uu.nl>: >> Is there a name for the following concept? Can you point me to any >> references on it? >> >> Suppose I have the following two functions ... >> >>> swap1 :: (Int, Char) -> (Char, Int) >>> swap2 :: (Char, Int) -> (Int, Char) >> >> ... and, for some reason, I think I can unify these into a single function. >> I think, hmm, given that the structure is that same, let's do a first pass: >> >>> swap? :: (a, b) -> (c, d) >> >> But then I go back to the input types to confirm that this will work, and, >> alas, it will not, because there are similarities that I missed. This is way >> too general. I need to ensure that what's an Int stays an Int and likewise >> for Char. >> >>> swap! :: (a, b) -> (b, a) >> >> And now I have found a type that is more general than swap1 and swap2 and >> yet not so general that the shared constraints are left out. This seems >> somewhat analogous to the least common multiple. >> >> Another example is the following: >> >>> showFloat :: Float -> String >>> showBool :: Bool -> String >> >> We could say the more general type is ... >> >>> show? :: a -> String >> >> ... but then we lose the implied constraint that we must know something >> about 'a' to produce a string. So, we add back such some such constraint: >> >>> show! :: (Show a) => a -> String >> >> Of course, with all of this, it may not be clear what to do about the >> definitions of the functions, but I'm curious if there's a name for the >> concept from a type perspective. >> >> Thanks, >> Sean >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > > > > -- > Eugene Kirpichov > Web IR developer, market.yandex.ru > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
