Abstract. Higher-order abstract syntax (HOAS) refers to the technique of representing variables of an object-language using variables of a meta-language. The standard first-order alternatives force the programmer to deal with superficial concerns such as substitutions, whose implementation is often routine, tedious, and error-prone. In this paper, we describe the underlying calculus of Delphin. Delphin is a fully implemented functional-programming language supporting reasoning over higher-order encodings and dependent types, while maintaining the benefits of HOAS. More specifically, just as representations utilizing HOAS free the programmer from concerns of handling explicit contexts and substitutions, our system permits programming over such encodings without making these constructs explicit, leading to concise and elegant programs. To this end our system distinguishes bindings of variables intended for instantiation from those that will remain uninstantiated, utilizing a variation of Miller and Tiu’s ∇-quantifier [1]. 1

We construct a logical framework supporting datatypes that mix binding and computation, implemented as a universe in the dependently typed programming language Agda 2. We represent binding pronominally, using well-scoped de Bruijn indices, so that types can be used to reason about the scoping of variables. We equip our universe with datatype-generic implementations of weakening, substitution, exchange, contraction, and subordination-based strengthening, so that programmers need not reimplement these operations for each individual language they define. In our mixed, pronominal setting, weakening and substitution hold only under some conditions on types, but we show that these conditions can be discharged automatically in many cases. Finally, we program a variety of standard difficult test cases from the literature, such as normalization-by-evaluation for the untyped λ-calculus, demonstrating that we can express detailed invariants about variable usage in a program’s type while still writing clean and clear code.

We define a dependent programming language in which programmers can define and compute with domain-specific logics, such as an access-control logic that statically prevents unauthorized access to controlled resources. Our language permits programmers to define logics using the LF logical framework, whose notion of binding and scope facilitates the representation of the consequence relation of a logic, and to compute with logics by writing functional programs over LF terms. These functional programs can be used to compute values at run-time, and also to compute types at compiletime. In previous work, we studied a simply-typed framework for representing and computing with variable binding [LICS 2008]. In this paper, we generalize our previous type theory to account for dependently typed inference rules, which are necessary to adequately represent domain-specific logics, and we present examples of using our type theory for certified software and mechanized metatheory.

Abstract. Delphin is a functional programming language [PS08] utilizing dependent higher-order datatypes. Delphin is a two level system, which cleanly separates data from computation. The data level is LF [HHP93], which allows for the specification of deductive systems following the judgments-as-types methodology utilizing higher-order abstract syntax (HOAS). The computation level facilitates the manipulation of such encodings by providing a newness constructor to create parameters (fresh constants) and the ability to write functions over parameters, which we also call parameter functions. A wealth of documentation and examples are available online at

Abstract. Nominal logic is an extension of first-order logic with features useful for reasoning about abstract syntax with bound names. For computational applications such as programming and formal reasoning, it is desirable to develop constructive type theories for nominal logic which extend standard type theories for propositional, first- or higher-order logic. This has proven difficult, largely because of complex interactions between nominal logic’s name-abstraction operation and ordinary functional abstraction. This difficulty already arises in the case of propositional logic and simple type theory. In this paper we show how this difficulty can be overcome, and present a simple nominal type theory which enjoys properties such as type soundness and strong normalization, and which can be soundly interpreted using existing nominal set models of nominal logic. We also sketch how recursion combinators for languages with binding structure can be provided. This is an important first step towards understanding the constructive content of nominal logic and incorporating it into existing logics and type theories. 1

We present MLSOS, a functional metalanguage for encoding definitions of structural operational semantics. The key features of this language are inbuilt support for representing object-language binding structures and performing proof-search. MLSOS uses the nominal approach to dealing with binders and a FreshML-style generative treatment of atoms. This allows us to prototype systems in a natural way, starting from a semi-formal specification. We outline the main design choices behind the language and illustrate its use. 1

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A wide range of computer programs, including compilers and theorem provers, manipulate data structures that involve names and binding. However, the design of programming idioms which allow performing these manipulations in a safe and natural style has, to a large extent, remained elusive. In this paper, we present a novel approach to the problem. Our proposal can be viewed either as a programming language design or as a library: in fact, it is currently implemented within Agda. enough to support multiple concrete implementations: we present one in nominal style and one in de Bruijn style. We use logical relations to prove that “well-typed programs do not mix names with different scope”. We exhibit an adequate encoding of Pitts-style nominal terms into our system. Keywords: names, binders, meta-programming, name abstraction, higher-order abstract syntax

This paper introduces a new recursion principle for inductive data modulo

Abstract. The logical framework LF provides an elegant foundation for specifying formal systems and proofs and it is used successfully in a wide range of applications such as certifying code and mechanizing metatheory of programming languages. However, incorporating LF technology into functional programming to allow programmers to specify and reason about formal guarantees of their programs from within the programming language itself has been a major challenge. In this paper, we present an overview of Beluga, a framework for programming and reasoning with formal systems. It supports specifying formal systems in LF and it also provides a dependently typed functional language that supports analyzing and manipulating LF data via pattern matching. A distinct feature of Beluga is its direct support for reasoning with contexts and contextual objects. Taken together these features lead to powerful language which supports writing compact and elegant proofs. 1