On Tue, 2009-06-30 at 18:31 -0700, John Meacham wrote:
On Tue, Jun 30, 2009 at 08:02:48PM -0400, Daniel Peebles wrote:
But we don't want to imply it's commutative either. Having something "bidirectional" like <> or <+> feels more commutative than associative to me.
Of course in Text.PrettyPrint, both <> and <+> are associative but not commutative (with identity empty).
Not really, think of '++', which doesn't commute but is visually symmetric, or Data.Sequence.<>, or the common use of <> to mean concatination in pretty printers. I think there is a fair amount of precedence for using '<>' actually. As it appears when it is used, it is also the natural mappend operator for the Monoid instance.
I agree, if we can't use ++ then <> is the next best thing. As John says it's already a monoid operator for Data.Sequence and Text.PrettyPrint. Duncan