25 Jun
2011
25 Jun
'11
9:02 p.m.
On Fri, Jun 24, 2011 at 11:13:46PM -0700, wren ng thornton wrote:
On 6/25/11 1:34 AM, Evan Laforge wrote:
So there's a range of possible Monoid instances for each type,
More for some types than for others. For Maybe there are three:
* always take the first/left value; * always take the last/right value; * or, use a semigroup operation defined on the values.
Actually, there are (at least) four: there's also the one where mappend = liftA2 mappend, i.e. introduce potential failure into a monoid operation defined on the values. I wrote about it here: http://byorgey.wordpress.com/2011/04/18/monoids-for-maybe/ -Brent