Wolfram Kahl writes:
On Mon, Aug 15, 2011 at 10:00:03AM +0900, Sebastian Fischer wrote:
I see your versions of + and * are infixr rather than infixl. Is that important?
I copied fixities from the Prelude [1] for + and * but don't know why they are infixl there.
Sorry, I just saw that I confused infixl and infixr in your question. In fact, in my two Semiring modules I use different fixities. infixr in the regexp library and infixl (copied from Prelude) in the (not yet published) library for parallel programming. So apparently, I don't care very much ;)
Are there good arguments in favor of or against either choice?
In the presence of - at the same precedence as + you want both to be infixl, to get:
a + b - c + d - e - f = ((((a + b) - c) + d) - e) - f
The same for * with /.
Yes: they need to be left associative for backwards compatibility, and it's an intuitive choice anyway.