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
