Yes, it may be quit hard to design such a combiner due to constraints both on the input (as the need for cross-chunk recombination), and on the output (as too e

Yes, it may be quit hard to design such a combiner due to constraints both on the input (as the need for cross-chunk recombination), and on the output (as too early finalization preventing further combinations); with the consequence that we often have to imagine a genuine intermediate data representation of the problem. But this complexity is mitigated by the fact that these associative combiners can be built incrementally using a reduced set of patterns, combiner compositions and transformations. Have a look to this remarkably well written post [1] on incremental regular expressions (it appears that incremental computation is deeply related with parallel computation). It shows well, on a non-trivial example, how to build such an intermediate data representation with its associative combiner. [1] http://jkff.info/articles/ire/ http://jkff.info/articles/ire/