Fix for juxtaposeDefault to correctly handle empty envelopes #24
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added 2 commits
August 31, 2012 16:30
envelopeV and envelopeP return the zero vector and origin, respectively, when called on an empty envelope. However, sometimes it's useful to actually know whether the envelope was empty or not (the zero vector and the origin are legitimate outputs from non-empty envelopes). The new functions have their return type wrapped in Maybe for this purpose.
In particular, juxtaposeDefault is now the identity on the second object if either one has an empty envelope. In particular this means that mempty is now an identity element for beside and friends.
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This fixes one part of diagrams/diagrams-lib#37 -- in particular, it means that
memptyis now an identity element forbesideand friends.I haven't yet investigated the other problem in that issue, but plan to look at it soon -- but it will most likely involve a patch to diagrams-lib.