John Hughes wrote: | `x := []' wouldn't be problematic, just monomorphic. | That is, x must be used consistently as a list of a | particular type.
Just to check if I understand you correctly. In your proposal, does the following thing share `x'? let x = fac 100 in x + x (My understanding is that, in order to do this in your proposal, we have to say: let x := fac 100 in x + x Correct?) Does this also mean that it becomes impossible to share polymorphic values? I.e. the following contrived example will not behave as usual: wrong :: Either String a wrong = Left (show (fac 100)) -- not shared? example1 :: Either String Int example1 := do wrong return 1 example2 :: Either String Char example2 := do wrong return 'a' (With the usual Either monad instance.) Of course, in this case, there is a perfect remedy, just lifting out `show (fac 100', which is a monomorphic expression. However, this is not always possible, we might have a datatype like this: data PolyMonoList a = Poly Int (Foo a) | Mono a (Foo a) | Nil We can construct rather large polymorphic values, which have to be converted in linear time to the same value of a different type. I guess we already have the problem of not being able to share monomorphic values polymorphically. In fact, the Either monad instance is a good example: instance Monad (Either e) where return = Right Left x >>= k = Left x Right a >>= k = k a In the definition of `>>=', it is impossible to share `Left x'. /Koen. _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell