Thank you, thank you, thank you. [This validates that my objection to our parametricity is real.]
On Nov 1, 2012, at 4:56 PM, John Clements wrote: > I can't tell whether this is a bug. In the program below, remove-duplicates > doesn't remove duplicates. This looks like an attempt to preserve > parametricity a la theorems for free, but I don't think that TR actually > tries to guarantee parametricity in this sense. I'm guessing that the values > in the list are being wrapped in contracts that prevent 'eq?'-checking; I > thought that chaperones were supposed to... no, I shouldn't even finish that > sentence. > > Anyhow, I'm just writing to make sure that this isn't a bug. It's certainly > not the behavior that I would naively expect. I can certainly work around the > bug by substituting a more specific type for remove-duplicates, as in the > commented-out version. > > John > > #lang typed/racket > > (require/typed racket > [remove-duplicates (All (T) (Listof T) -> (Listof T))] > #;[remove-duplicates ((Listof Symbol) -> (Listof Symbol))]) > > (remove-duplicates '(a b c a d)) ;; => produces '(a b c a d)--that is, a list > with duplicates > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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