Skip to main content

Streaming Representation−Changers

Jeremy Gibbons

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.

Book Title
Mathematics of Program Construction
Editor
Dexter Kozen
Month
jul
Pages
142−168
Series
Lecture Notes in Computer Science
Volume
3125
Year
2004