In the paper on compact regions (http://ezyang.com/papers/ezyang15-cnf.pdf), we find the following:
However, if we want to apply a functional update to this tree, we may want to specify the already existing compact region so we can reuse any already compacted shared data... appendCompact, like newCompact, fully evaluates a; however, it copies the result into the same compact region as Compact b. Additionally, it short-circuits the evaluation/copying process if a subgraph is already in the target compact region.
However, in the docs for both the compact library and the ghc-compact library (still only on phabricator), this short-circuiting behavior is not mentioned. Did this end up in the final implementation on was it dropped? If it is implemented, I think it's worth mentioning in the docs for `compactAdd`. -Andrew Martin