Region-based memory management is an alternative to standard tracing garbage collection that makes potentially dangerous operations such as memory deallocation explicit but verifiably safe. In this article, we present a new compiler intermediate language, called the Capability Calculus, that supports region-based memory management and enjoys a provably safe type system. Unlike previous region-based type systems, region lifetimes need not be lexically scoped and yet the language may be checked for safety without complex analyses. Therefore, our type system may be deployed in settings such as extensible operating systems where both the performance and safety of untrusted code is important.

There has already been considerable research on constructing modular, monad-based specications of computational effects (state, exceptions, nondeterminism, etc.) in programming languages. We present a simple framework in this tradition, based on a Church-style effect-typing system for an ML-like language. The semantics of this language is formally dened by a series of monadic translations, each one expanding away a layer of effects. Such a layered specication is easy to reason about, but its direct implementation (whether by parameterized interpretation or by actual translation) is often prohibitively inefficient. By exploiting deeper semantic properties of monads, however, it is also possible to derive a vastly more efficient implementation: we show that each layer of eects can be uniformly simulated by continuation-passing, and further that multiple such layers can themselves be simulated by a standard semantics for call/cc and mutable state. Thus, even multi-effect programs can be execu...

This is a tutorial on using type-indexed embedding/projection pairs when writing interpreters in statically-typed functional languages. The method allows (higher-order) values in the interpreting language to be embedded in the interpreted language and values from the interpreted language may be projected back into the interpreting one. This is particularly useful when adding command-line interfaces or scripting languages to applications written in functional languages. We first

Motivated by many practical applications that have to compute in the presence of uncertainty, we propose a monadic probabilistic language based upon the mathematical notion of sampling function. Our language provides a unified representation scheme for probability distributions, enjoys rich expressiveness, and o#ers high versatility in encoding probability distributions. We also develop a novel style of operational semantics called a horizontal operational semantics, under which an evaluation returns not a single outcome but multiple outcomes. We have preliminary evidence that the horizontal operational semantics improves the ordinary operational semantics with respect to both execution time and accuracy in representing probability distributions.

We propose an axiomatization of fixpoint operators in typed call-by-value programming languages, and give its justifications in two ways. First, it is shown to be sound and complete for the notion of uniform T-fixpoint operators of Simpson and Plotkin. Second, the axioms precisely account for Filinski's fixpoint operator derived from an iterator (infinite loop constructor) in the presence of firstclass continuations, provided that we define the uniformity principle on such an iterator via a notion of effect-freeness (centrality). We then explain how these two results are related in terms of the underlying categorical structures.

In their purest formulation, monads are used in functional programming for two purposes: (1) to hygienically propagate effects, and (2) to globalize the effect scope -- once an effect occurs, the purity of the surrounding computation cannot be restored. As a consequence, monadic typing does not provide very naturally for the practically important ability to handle effects, and there is a number of previous works directed toward remedying this deficiency. It is mostly based on extending the monadic framework with further extra-logical constructs to support handling. In this paper we adopt...

The presence of side eects in even a very simple language of expressions gives rise to a number of semantic questions. The issue of evaluation order becomes a crucial one and, unless a specic order is enforced, the language becomes non-deterministic. In this paper we study the denotational semantics of such a language under a variety of possible evaluation strategies, from simpler to more complex, concluding with unspecied evaluation order, unspecied order of side eects and the mechanism of sequence points that is particular to the ANSI C programming language. In doing so, we adopt a dialect of Haskell as a metalanguage, instead of mathematical notation, and use monads and monad transformers to improve modularity. In this way, only small modications are required for each transition. The result is a better understanding of dierent evaluation strategies and a unied way of specifying their semantics. Furthermore, a signicant step is achieved towards a complete and accurate semant...

In this paper we present an implementation of a Standard ML combinator library for serializing and deserializing data structures. The combinator library supports serialization of cyclic data structures and sharing. It generates compact serialized values, both due to sharing, but also due to type specialization. The library is type safe in the sense that a type specialized serializer can be applied only to values of the specialized type. In the paper, we demonstrate how programmer control provided by the combinator library can lead to e#cient serializers compared to how values are serialized with generic serializers supported by traditional language implementations.