Re: Elimination of absurd patterns
On Mon, May 2, 2011 at 6:20 PM, C Rodrigues wrote: > I was experimenting with using GADTs for subtyping when I found something > interesting. Hopefully someone can satisfy my curiosity. > Here are two equivalent GADTs. My understanding was that GHC would > translate "Foo" and "Bar" into isomorphic data types. However, GHC 6.12.3 > generates better code for 'fooName' than for 'barName'. In 'fooName', there > is no pattern match against 'FooExtra'. In 'barName', there is a pattern > match against 'BarExtra'. What makes these data types different? IIRC, GHC 6.12.3 had some problems with type equalities. Did you try GHC 7.0.3? Cheers, =) -- Felipe. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Elimination of absurd patterns (reformatted)
On Mon, May 02, 2011 at 09:25:06PM +, C Rodrigues wrote: > > I'm re-sending this e-mail, hopefully with proper line breaks this time. > > I was experimenting with using GADTs for subtyping when I found something > interesting. Hopefully someone can satisfy my curiosity. > > Here are two equivalent GADTs. My understanding was that GHC would translate > "Foo" and "Bar" into isomorphic data types. > However, GHC 6.12.3 generates better code for 'fooName' than for 'barName'. > In 'fooName', there is no pattern match against 'FooExtra'. > In 'barName', there is a pattern match against 'BarExtra'. What > makes these data types different? Not a real answer to your question, but have you tried this with GHC 7.0.3? The type checker changed a lot between 6.12 and 7 and it may now behave more consistently (although I do not know for sure). -Brent ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Elimination of absurd patterns (reformatted)
I'm re-sending this e-mail, hopefully with proper line breaks this time. I was experimenting with using GADTs for subtyping when I found something interesting. Hopefully someone can satisfy my curiosity. Here are two equivalent GADTs. My understanding was that GHC would translate "Foo" and "Bar" into isomorphic data types. However, GHC 6.12.3 generates better code for 'fooName' than for 'barName'. In 'fooName', there is no pattern match against 'FooExtra'. In 'barName', there is a pattern match against 'BarExtra'. What makes these data types different? data Tag data TagExtra data Foo a where Foo :: String -> Foo a FooExtra :: IORef String -> Foo TagExtra -- The cmm code for fooName does not match against 'FooExtra' fooName :: Foo Tag -> String fooName (Foo s) = s data Bar a where Bar :: String -> Bar a BarExtra :: a ~ TagExtra => IORef String -> Bar a -- The cmm code for barName will try to pattern-match against 'BarExtra' barName :: Bar Tag -> String barName (Bar s) = s ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Elimination of absurd patterns
I was experimenting with using GADTs for subtyping when I found something interesting. Hopefully someone can satisfy my curiosity. Here are two equivalent GADTs. My understanding was that GHC would translate "Foo" and "Bar" into isomorphic data types. However, GHC 6.12.3 generates better code for 'fooName' than for 'barName'. In 'fooName', there is no pattern match against 'FooExtra'. In 'barName', there is a pattern match against 'BarExtra'. What makes these data types different? data Tagdata TagExtra data Foo a where Foo :: String -> Foo a FooExtra :: IORef String -> Foo TagExtra -- The cmm code for fooName does not match against 'FooExtra'fooName :: Foo Tag -> StringfooName (Foo s) = s data Bar a where Bar :: String -> Bar a BarExtra :: a ~ TagExtra => IORef String -> Bar a -- The cmm code for barName will try to pattern-match against 'BarExtra'barName :: Bar Tag -> StringbarName (Bar s) = s ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
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