[Haskell-cafe] Problem with class Control.Monad.Error noMsg usage

Tue, 21 Dec 2010 07:31:03 -0800 

I have been trying to build the Scheme in 24 Hours on WikiBooks :-

    http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours

    http://jonathan.tang.name/files/scheme_in_48/code/listing10.hs

But I am getting an error :-

    scheme.hs:289:6: `noMsg' is not a (visible) method of class `Error'

    scheme.hs:290:6:
         `strMsg' is not a (visible) method of class `Error'

with the following :-

    instance Error LispError where
         noMsg = Default "An error has occurred"
         strMsg = Default

if I try importing them :-

    import Control.Monad.Error (noMsg, strMsg)

I get the following :-

    scheme.hs:4:29:
        Module `Control.Monad.Error' does not export `noMsg'

    scheme.hs:4:36:
        Module `Control.Monad.Error' does not export `strMsg'

Many thanks in advance,

Aaron

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