On Sat, Jun 25, 2011 at 02:34:47PM -0700, Evan Laforge wrote:
On Sat, Jun 25, 2011 at 2:02 PM, Brent Yorgey byor...@seas.upenn.edu wrote:
Actually, there are (at least) four: there's also the one where
mappend = liftA2 mappend, i.e. introduce potential failure into a
monoid operation
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
So is there a typeclass for that?
There might be one hidden in one of the attempts at redesigning the
numeric hierarchy (e.g., Numeric Prelude), but there's not a canonical
typeclass for them. Unfortunately it's not really a good match for the
typeclass system since it doesn't introduce any
On Fri, 24 Jun 2011, Evan Laforge wrote:
So there's a range of possible Monoid instances for each type, and
maybe they were chosen by historical happenstance rather than some
kind of principle monoid (is there such a thing?). Is there a name
for the thing that's like a monoid, but the
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
On Sat, Jun 25, 2011 at 2:02 PM, Brent Yorgey byor...@seas.upenn.edu wrote:
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:
Not being especially mathematically inclined, every once and a while I
get a little panicked when I notice that, e.g. Data.Map mappend is a
plain left-biased union, and doesn't actually mappend the values of
the map.
Then I remember that monoids are associative, not commutative, and
it's totally
