| Maintainer | diagrams-discuss@googlegroups.com |
|---|---|
| Safe Haskell | Safe-Inferred |
Data.Monoid.Split
Description
Sometimes we want to accumulate values from some monoid, but have the ability to introduce a "split" which separates values on either side. Only the rightmost split is kept. For example,
a b c | d e | f g h == a b c d e | f g h
In the diagrams graphics framework this is used when accumulating
transformations to be applied to primitive diagrams: the freeze
operation introduces a split, since only transformations occurring
outside the freeze should be applied to attributes.
Documentation
A value of type Split m is either a single m, or a pair of
m's separated by a divider. Single m's combine as usual;
single m's combine with split values by combining with the
value on the appropriate side; when two split values meet only
the rightmost split is kept, with both the values from the left
split combining with the left-hand value of the right split.
Data.Monoid.Cut is similar, but uses a different scheme for
composition. Split uses the asymmetric constructor :|, and
Cut the symmetric constructor :||:, to emphasize the inherent
asymmetry of Split and symmetry of Cut. Split keeps only
the rightmost split and combines everything on the left; Cut
keeps the outermost splits and throws away everything in between.
Instances
| Show m => Show (Split m) | |
| (Semigroup m, Monoid m) => Monoid (Split m) | |
| Semigroup m => Semigroup (Split m) | If |
| Action m n => Action (Split m) n | By default, the action of a split monoid is the same as for the underlying monoid, as if the split were removed. |