We present a dependently typed assembly language (DTAL) in which the type system supports the use of a restricted form of dependent types, reaping some benefits of dependent types at assembly level. DTAL overcomes several significant limitations in recently proposed low-level languages including Java bytecode language and a typed assembly language, which prevent them from handling certain important compiler optimizations such as run-time array bound check elimination. We also mention a compiler which can generate DTAL code from compiling some high-level programs. 1

Recent advances in compiler technology have demonstrated the benefits of using strongly typed intermediate languages to compile richly typed source languages (e.g., ML). A typepreserving compiler can use types to guide advanced optimizations and to help generate provably secure mobile code. Types, unfortunately, are very hard to represent and manipulate efficiently; a naive implementation can easily add exponential overhead to the compilation and execution of a program. This paper describes our experience with implementing the FLINT typed intermediate language in the SML/NJ production compiler. We observe that a type-preserving compiler will not scale to handle large types unless all of its type-preserving stages preserve the asymptotic time and space usage in representing and manipulating types. We present a series of novel techniques for achieving this property and give empirical evidence of their effectiveness.

Compilers for polymorphic languages can use runtime type inspection to support advanced implementation techniques such as tagless garbage collection, polymorphic marshalling, and flattened data structures. Intensional type analysis is a type-theoretic framework for expressing and certifying such type-analyzing computations. Unfortunately, existing approaches to intensional analysis do not work well on types with universal, existential, or fixpoint quantifiers. This makes it impossible to code applications such as garbage collection, persistence, or marshalling which must be able to examine the type of any runtime value. We present a typed intermediate language that supports fully reflexive intensional type analysis. By fully reflexive, we mean that type-analyzing operations are applicable to the type of any runtime value in the language. In particular, we provide both type-level and term-level constructs for analyzing quantified types. Our system supports structural induction on quant...

Typed assembly languages provide a way to generate machinecheckable safety proofs for machine-language programs. But the soundness proofs of most existing typed assembly languages are hand-written and cannot be machine-checked, which is worrisome for such large calculi. We have designed and implemented a low-level typed assembly language (LTAL) with a semantic model and established its soundness from the model. Compared to existing typed assembly languages, LTAL is more scalable and more secure; it has no macro instructions that hinder low-level optimizations such as instruction scheduling; its type constructors are expressive enough to capture dataflow information, support the compiler's choice of data representations and permit typed position-independent code; and its type-checking algorithm is completely syntax-directed.

A tension in language design has been between simple semantics on the one hand, and rich possibilities for side-effects, exception handling and so on on the other. The introduction of monads has made a large step towards reconciling these alternatives. First proposed by Moggi as a way of structuring semantic descriptions, they were adopted by Wadler to structure Haskell programs, and now offer a general technique for delimiting the scope of effects, thus reconciling referential transparency and imperative operations within one programming language. Monads have been used to solve long-standing problems such as adding pointers and assignment, inter-language working, and exception handling to Haskell, without compromising its purely functional semantics. The course will introduce monads, effects and related notions, and exemplify their applications in programming (Haskell) and in compilation (MLj). The course will present typed metalanguages for monads and related categorica...

9706572, and the US Air Force under grant F19628-95-C-0050 and a generous fellowship. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressed or implied, of any sponsoring institution, the U.S. government or any other entity.

Abstract. We propose a simple compositional program logic for an imperative extension of call-by-value PCF, built on Hoare logic and our preceding work on program logics for pure higher-order functions. A systematic use of names and operations on them allows precise and general description of complex higher-order imperative behaviour. The proof rules of the logic exactly follow the syntax of the language and can cleanly embed, justify and extend the standard proof rules for total correctness of Hoare logic. The logic offers a foundation for general treatment of aliasing and local state on its basis, with minimal extensions. After establishing soundness, we prove that valid assertions for programs completely characterise their behaviour up to observational congruence, which is proved using a variant of finite canonical forms. The use of the logic is illustrated through reasoning examples which are hard to assert and infer using existing program logics.

We present an efficient encoding of core Java constructs in a simple, implementable typed intermediate language. The encoding, after type erasure, has the same operational behavior as a standard implementation using vtables and selfapplication for method invocation. Classes inherit super-class methods with no overhead. We support mutually recursive classes while preserving separate compilation. Our strategy extends naturally to a significant subset of Java, including interfaces and privacy. The formal translation using Featherweight Java allows comprehensible type-preservation proofs and serves as a starting point for extending the translation to new features.

Higher-order modules are very effective in structuring large programs and defining generic, reusable software components. Unfortunately, many compilation techniques for the core languages do not work across the module boundaries. As a result, few optimizing compilers support these module facilities well. This paper exploits the semantic property of ML-style modules to support efficient cross-module compilation. More specifically, we present a type-directed translation of the MacQueen-Tofte higher-order modules into a predicative variant of the polymorphic -calculus F! . Because modules can be compiled in the same way as ordinary polymorphic functions, standard type-based optimizations such as representation analysis immediately carry over to the module languages. We further show that the full-transparency property of the MacQueen-Tofte system yields a near optimal cross-module compilation framework. By propagating various static information through the module boundaries, many static pr...

The following paper was originally published in the