Computation is a physical process which, like all other physical processes, is fundamentally reversible. From the notion of type isomorphisms, we derive a typed, universal, and reversible computational model in which information is treated as a linear resource that can neither be duplicated nor erased. We use this model as a semantic foundation for computation and show that the "gap" between conventional irreversible computation and logically reversible computation can be captured by a type-and-effect system. Our type-and-effect system is structured as an arrow metalanguage that exposes creation and erasure of information as explicit effect operations. Irreversible computations arise from interactions with an implicit information environment, thus making them a derived notion, much like open systems in Physics. We sketch several applications which can benefit from an explicit treatment of information effects, such as quantitative information-flow security and differential privacy.

We present a parallel generational-copying garbage collector implemented for the Glasgow Haskell Compiler. We use a block-structured memory allocator, which provides a natural granularity for dividing the work of GC between many threads, leading to a simple yet effective method for parallelising copying GC. The results are encouraging: we demonstrate wall-clock speedups of on average a factor of 2 in GC time on a commodity 4-core machine with no programmer intervention, compared to our best sequential GC.