The integration of first-order and higher-order paradigms has been one of the main challenges in the design of both declarative programming languages and proof environments. It has led to the development of new computation models and new logical frameworks, which have been obtained by enriching first-order rewriting with higher-order capabilities or by adding algebraic features to the λ-calculus.

Pure Pattern Type Systems (P2TS) combine the frameworks and capabilities of rewriting and λ-calculus within a unified setting. Their type systems, which are adapted from Barendregt's λ-cube, are especially interesting from a logical point of view. Until now, strong normalisation, which is an essential property for logical soundness, has only been conjectured: in this paper, we give a positive answer for the simply-typed system and the dependently-typed system.

The proof is based on a translation of terms and types from P2TS into the λ-calculus. First, we deal with untyped terms, ensuring that reductions are faithfully mimicked in the λ-calculus. For this, we rely on an original encoding of the pattern matching capability of P2TS into the System Fω.

Then we show how to translate types: the expressive power of System Fω is needed in order to fully reproduce the original typing judgments of P2TS. We prove that the encoding is correct with respect to reductions and typing, and we conclude with the strong normalisation of simply-typed P2TS terms. The strong normalisation with dependent types is in turn obtained by an intermediate translation into simply-typed terms.

We propose an imperative version of the Rewriting Calculus, a calculus based on pattern matching, pattern abstraction and side effects, which we call iRho.

We formulate both a static and big-step call-by-value operational semantics of iRho. The operational semantics is deterministic, and immediately suggests how an interpreter for the calculus may be built. The static semantics is given using a first-order type system based on a form of product types, which can be assigned to term-like structures (that is, records).

The calculus is à la Church, that is, pattern abstractions are decorated with the types of the free variables of the pattern.

iRho is a good candidate for the core of a pattern-matching imperative language, where a (monomorphic) typed store can be safely manipulated and where fixed points are built into the language itself.

Properties such as determinism of the interpreter and subject-reduction have been completely checked using a machine-assisted approach with the Coq proof assistant. Progress and decidability of type checking are proved using pen and paper.

We present a higher-order call-by-need lambda calculus enriched with constructors, case expressions, recursive letrec expressions, a seq operator for sequential evaluation and a non-deterministic operator amb that is locally bottom-avoiding. We use a small-step operational semantics in the form of a single-step rewriting system that defines a (non-deterministic) normal-order reduction. This strategy can be made fair by adding resources for book-keeping. As equational theory, we use contextual equivalence (that is, terms are equal if, when plugged into any program context, their termination behaviour is the same), in which we use a combination of may- and must-convergence, which is appropriate for non-deterministic computations. We show that we can drop the fairness condition for equational reasoning, since the valid equations with respect to normal-order reduction are the same as for fair normal-order reduction. We develop a number of proof tools for proving correctness of program transformations. In particular, we prove a context lemma for both may- and must- convergence that restricts the number of contexts that need to be examined for proving contextual equivalence. Combining this with so-called complete sets of commuting and forking diagrams, we show that all the deterministic reduction rules and some additional transformations preserve contextual equivalence. We also prove a standardisation theorem for fair normal-order reduction. The structure of the ordering ≤c is also analysed, and we show that Ω is not a least element and ≤c already implies contextual equivalence with respect to may-convergence.

is an untyped continuation-style formal language with a typed subset that provides a Curry–Howard isomorphism for a sequent calculus for implicative classical logic. can also be viewed as a language for describing nets by composition of basic components connected by wires. These features make an expressive platform on which many different (applicative) programming paradigms can be mapped. In this paper we will present the syntax and reduction rules for ; in order to demonstrate its expressive power, we will show how elaborate calculi can be embedded, such as the λ-calculus, Bloo and Rose's calculus of explicit substitutions λx, Parigot's λμ and Curien and Herbelin's .

was first presented in Lengrand (2003), where it was called the λξ-calculus. It can be seen as the pure untyped computational content of the reduction system for the implicative classical sequent calculus of Urban (2000).

In this paper we introduce the concept of Kleisli strength for monads in an arbitrary symmetric monoidal category. This generalises the notion of commutative monad and gives us new examples, even in the cartesian-closed category of sets. We exploit the presence of Kleisli strength to derive methods for generating distributive laws. We also introduce linear equations to extend the results to certain quotient monads. Mechanisms are described for finding strengths that produce a large collection of new distributive laws, and consequently monad compositions, including the composition of monadic data types such as lists, trees, exceptions and state.