On Friday 19 September 2003 12:09 pm, MR K P SCHUPKE wrote:

Would it not be better to have control over exactly where these options apply, could you not have:

{-# OPTIONS fallow-overlapping-instances=true #-}

... some code ...

{-# OPTIONS -fallow-overlapping-instances=false #-}

... more code ...

So you can ensure instances you don't want overlapping cannot?

That works for syntactic extensions - we just have to tweak the parser so that rules are enabled or diabled accordingly. (I'm not sure if it's very useful but it can be done.) It doesn't work all that well for typesystem extensions because Haskell's typechecker requires definitions to be reordered so that every function definition is as local as possible. It is also hard to have code compiled with one typechecker call code compiled with a different typechecker - for example, I'm told that making Hugs '-98' flag a per-module option is not viable. -- Alastair Reid