Overloaded function and implicit parameter passing
Hi. While experimenting with the implicit parameter extension to Haskell 98, implemented in GHC 4.08.1 and latest Hugs, I came accross a difference among those implementations regarding overloading functions with implicit parameters. As a test consider the program ------------------------- cut here module Main where class C a where f :: (?env :: Integer) => a -> Integer instance C Integer where f x = ?env + x main = putStrLn (show (f (45::Integer) with ?env = 100)) ------------------------- cut here Hugs accepts this program and outputs 145, as expected. But GHC 4.08.1 refuses to compile it, emitting the message $ ghc -fglasgow-exts Test1.hs -o test1 Test1.hs:7: Unbound implicit parameter `env_rJX :: Integer' arising from use of `env_rJX' at Test1.hs:7 In the first argument of `+', namely `env_rJX' In the right-hand side of an equation for `f': env_rJX + x Compilation had errors Would anybody comment on what is going on with GHC? I am willing to use implicit parameters in the software I am developing, but I have the need to overload functions with implicit parameters. While Hugs is good for development, its performance may rule it out when the final product is ready. So I will need a good Haskell compiler to compile my system. Any comments? Romildo -- Prof. José Romildo Malaquias <romildo@iceb.ufop.br> Departamento de Computação Universidade Federal de Ouro Preto Brasil
On 23-Oct-2000, José Romildo Malaquias <romildo@urano.iceb.ufop.br> wrote:
------------------------- cut here module Main where
class C a where f :: (?env :: Integer) => a -> Integer
instance C Integer where f x = ?env + x
main = putStrLn (show (f (45::Integer) with ?env = 100)) ------------------------- cut here ... $ ghc -fglasgow-exts Test1.hs -o test1
Test1.hs:7: Unbound implicit parameter `env_rJX :: Integer' arising from use of `env_rJX' at Test1.hs:7 ... Would anybody comment on what is going on with GHC?
That sure looks to me like a bug in GHC's support for implicit parameter passing. -- Fergus Henderson <fjh@cs.mu.oz.au> | "I have always known that the pursuit | of excellence is a lethal habit" WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.
José Romildo Malaquias wrote:
Hi.
While experimenting with the implicit parameter extension to Haskell 98, implemented in GHC 4.08.1 and latest Hugs, I came accross a difference among those implementations regarding overloading functions with implicit parameters.
As a test consider the program
------------------------- cut here module Main where
class C a where f :: (?env :: Integer) => a -> Integer
instance C Integer where f x = ?env + x
main = putStrLn (show (f (45::Integer) with ?env = 100)) ------------------------- cut here
Hugs accepts this program and outputs 145, as expected. But GHC 4.08.1 refuses to compile it, emitting the message
$ ghc -fglasgow-exts Test1.hs -o test1
Test1.hs:7: Unbound implicit parameter `env_rJX :: Integer' arising from use of `env_rJX' at Test1.hs:7 In the first argument of `+', namely `env_rJX' In the right-hand side of an equation for `f': env_rJX + x
Compilation had errors
Would anybody comment on what is going on with GHC?
I am willing to use implicit parameters in the software I am developing, but I have the need to overload functions with implicit parameters. While Hugs is good for development, its performance may rule it out when the final product is ready. So I will need a good Haskell compiler to compile my system.
Any comments?
Certainly a bug. I'll look at it when I get a chance. --Jeff
participants (3)
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Fergus Henderson -
Jeffrey R. Lewis -
José Romildo Malaquias