Oleg, Another puzzle is that: instance Show a => Monoidable a String where toMonoid a = show a main = putStrLn $ unwrap $ polyToMonoid "" True () (Just (5::Int)) works just fine, but instance Show a => Monoidable a [String] where toMonoid a = [show a] main = putStrLn $ unwrap $ polyToMonoid [] True () (Just (5::Int)) fails to compile. Why would that be? My understanding is that all lists are automatically monoids. Kevin On Oct 9, 2:28 pm, Kevin Jardine <kevinjard...@gmail.com> wrote:
Hi Bartek,
Yes, it compiles, but when I try to use polyToMonoid', it turns out that this function is no longer polyvariadic, unlike the original polyToMonoid .
This may be what Luke meant when he wrote "you lose composability".
Even with the extra unwrap function I think that this is pretty cool, but I would ideally like to hide the unwrap.
Kevin
On Oct 9, 1:50 pm, Bartek Æwik³owski <paczesi...@gmail.com> wrote:
Hello Kevin,
2010/10/9 Kevin Jardine <kevinjard...@gmail.com>:
I was attempting to turn this into a small library and wanted to avoid exporting unwrap.
I defined:
polyToMonoid' = unwrap . polyToMonoid
If you disable MonomorphismRestriction this definition typechecks just fine. Alternatively, you can ask ghci about the type of "unwrap . polyToMonoid" and paste that into the type sig.
regards, Bartek Æwik³owski _______________________________________________ Haskell-Cafe mailing list Haskell-C...@haskell.orghttp://www.haskell.org/mailman/listinfo/haskell-cafe
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