Metamorphisms

Dr Jeremy Gibbons

Computing Laboratory, Oxford University

Fri Feb 25 15:10:00 NZDT 2005 in Room 031, MSCS

Abstract

Unfolds generate data structures, and folds consume them. A hylomorphism is a fold after an unfold, generating then consuming a virtual data structure. A metamorphism is the opposite composition, an unfold after a fold; typically, it will convert from one data representation to another. In general, metamorphisms are less interesting than hylomorphisms: there is no automatic fusion to deforest the intermediate virtual data structure. However, under certain conditions fusion is possible: some of the work of the unfold can be done before all of the work of the fold is complete. This permits streaming metamorphisms, and among other things allows conversion of infinite data representations. We present the theory of metamorphisms and outline some examples. (See http://www.comlab.ox.ac.uk/oucl/work/jeremy.gibbons/publications/index.html#metamorphisms-scp).