n+k patterns

[Ross Paterson]

On Tue, Jan 29, 2002 at 07:36:56AM -0800, Simon Peyton-Jones wrote:
> The Haskell Report says of n+k patterns:
> 
> "A n+k pattern can only be matched against a value in 
> the class Integral."
> 
> This seems far too strong.   All that is needed are Ord (for the >=)
> and Num (for - and fromInteger), and indeed that's what GHC requires. 
> Do Hugs or nhc actually require Integral?

Hugs demands Integral and the assumption that only one class is involved
seems deeply entwined in the code.

> In any case,  I propose to change "Integral" to "Ord and Num".

Without this change, the relevant rule of the formal semantics of patterns
wouldn't preserve the static semantics.