= Lift the monomorphism restriction =

We could simply remove the M-R from the language, but suggest that implementations issue a warning when a loss of sharing might occur due to overloading of a variable or pattern binding.  

The warning would not be mandatory - the report doesn't mandate implementation behaviour of this kind, rather it would be a recommendation.  To make the warning mandatory would require talking about operational semantics, which the report also doesn't do.

'''For:'''
 * Simple, removes a wart from the language
 * "As much polymorphism as possible" is in the spirit of Haskell - it is strange to limit polymorphism for performance reasons (indeed, this is arguably a poor compromise)
 * It turns out to be quite hard to demonstrate a performance problem due to the M-R, at least with GHC, because its optimiser often recovers the sharing.
 * Even if you do get loss of sharing, profiling will quickly pinpoint it
 * nhc98 has never implemented the M-R, and users haven't found any significant problems as a result
 * Hugs has a different (non-Haskell98) implementation of the M-R
 * Haskell doesn't specify an evaluation strategy so introducing the concept of 'sharing' is strange indeed.

'''Against:'''
 * Might be hard to give an accurate warning; just warning about overloaded variable bindings isn't good enough, because they don't all result in loss of sharing.
 * The warning might be confusing to new users (but if we could make it accurate, it wouldn't happen much)
 * For cases where you want the polymorphic type and don't want to write a type signature, then having the compiler emit a warning by default is undesirable.