Maintainer | diagrams-discuss@googlegroups.com |
---|---|

Safe Haskell | Safe-Inferred |

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.

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. |