On Tue, Sep 20, 2011 at 10:59 AM, Chris Smith
The better way to look at this is that the notion of `succ` and `pred` is dependent on the type, much like `mappend` has no particular meaning until a Monoid instance is given for the type. It's fairly well established, though undocumented, that Num types ought to have succ = (+1) and pred = (subtract 1), so if your fixed point type doesn't do that, I'd suggest it is the problematic part of this.
I forgot to address this in my last email. I disagree that it is well established for succ = (+1) and pred = subtract 1 for Num instances. In fact, for types that are also instances of Bounded where the Num instances have overflow this is required to be *not* true. Not realizing this is a often a source of performance problems or even bugs in Haskell programs. - Jake