3 ms·
It can appear in the range (making up assignment syntax here) foo :: (Num a, HasField "slot" a b) => b -> b foo x = x.slot <~ 1 Technically, depending
by tel 12y ago
It can appear in the range (making up assignment syntax here)
foo :: (Num a, HasField "slot" a b) => b -> b
foo x = x.slot <~ 1
Technically, depending upon the semantics of records (how anonymous they are) it could even be that the input argument has a different type as the output argument, e.g.
foo {} ==> {slot = 1}
Anyway, there's a lot to be said here but I think that this isn't merely a syntactic difference. Even the idea that
map (\x -> x.slot) listOfFoos
could be inferred would require mixing type inference and syntax de-sugaring.
- yummyfajitas 12y agoShould have said "if it can't appear in the domain, it can't appear in the range". Obviously if it appears in the domain it can also get into the range - a simpler example with real syntax is \x -> x. What I'm arguing is that anonymous records are unnecessary and it's silly to insist that problems with anonymous records should derail a good solution for concrete ones. But you are right that it's a bit more than just syntactic.