Combining Effects: Sum and Tensor

J. M. E. Hyland, Gordon Plotkin, A. J. Power

Research output: Contribution to journalArticlepeer-review


We seek a unified account of modularity for computational effects. We begin by reformulating Moggi's monadic paradigm for modelling computational effects using the notion of enriched Lawvere theory, together with its relationship with strong monads; this emphasises the importance of the operations that produce the effects. Effects qua theories are then combined by appropriate bifunctors on the category of theories. We give a theory for the sum of computational effects, which in particular yields Moggi's exceptions monad transformer and an interactive input/output monad transformer. We further give a theory of the commutative combination of effects, their tensor, which yields Moggi's side-effects monad transformer. Finally, we give a theory of operation transformers, for redefining operations when adding new effects; we derive explicit forms for the operation transformers associated to the above monad transformers.
Original languageEnglish
Pages (from-to)70-99
Number of pages30
JournalTheoretical Computer Science
Issue number1-3
Publication statusPublished - 2006

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