On Sat, Jun 25, 2011 at 19:07, Evan Laforge <[email protected]> wrote: > On Sat, Jun 25, 2011 at 9:00 AM, Jens Blanck <[email protected]> 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.
Brent Yorgey recently blogged about a fourth instance [1] which also uses the semigroup operation on the values, but treats Nothing as failure, returning Nothing. Erik [1] https://byorgey.wordpress.com/2011/04/18/monoids-for-maybe/ _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
