This paper presents a type-based information flow analysis for a call-by-value λ-calculus equipped with references, exceptions and let-polymorphism, which we refer to as Core ML. The type system is constraint-based and has decidable type inference. Its noninterference proof is reasonably light-weight, thanks to the use of a number of orthogonal techniques. First, a syntactic segregation between values and expressions allows a lighter formulation of the type system. Second, noninterference is reduced to subject reduction for a nonstandard language extension. Lastly, a semi-syntactic approach to type soundness allows dealing with constraint-based polymorphism separately.

Soft type systems provide the benefits of static type checking for dynamically typed languages without rejecting untypable programs. A soft type checker infers types for variables and expressions and inserts explicit run-time checks to transform untypable programs to typable form. We describe a practical soft type system for R4RS Scheme. Our type checker uses a representation for types that is expressive, easy to interpret, and supports efficient type inference. Soft Scheme supports all of R4RS Scheme, including procedures of fixed and variable arity, assignment, continuations, and top-level definitions. Our implementation is available by anonymous FTP. The first author was supported in part by the United States Department of Defense under a National Defense Science and Engineering Graduate Fellowship. y The second author was supported by NSF grant CCR-9122518 and the Texas Advanced Technology Program under grant 003604-014. 1 Introduction Dynamically typed languages like Scheme...

... This paper develops type systems which can statically guarantee the success of these checks. Our systems allow security properties of programs to be clearly expressed within the types themselves, which thus serve as static declarations of the security policy. We develop these systems using a systematic methodology: we show that the security-passing style translation, proposed by Wallach, Appel and Felten as a dynamic implementation technique, also gives rise to static security-aware type systems, by composition with conventional type systems. To de ne the latter, we use the general HM(X) framework, and easily construct several constraint- and unification-based type systems.

This paper presents a program analysis to estimate uncaught exceptions in ML programs. This analysis relies on unification-based type inference in a non-standard type system, using rows to approximate both the flow of escaping exceptions (a la effect systems) and the flow of result values (a la control-flow analyses). The resulting analysis is efficient and precise; in particular, arguments carried by exceptions are accurately handled.

Soft typing is an approach to type checking for dynamically typed languages. Like a static type checker, a soft type checker infers syntactic types for identifiers and expressions. But rather than reject programs containing untypable fragments, a soft type checker inserts explicit run-time checks to ensure safe execution. Soft typing was first introduced in an idealized form by Cartwright and Fagan. This thesis investigates the issues involved in designing a practical soft type system. A soft type system for a purely functional, call-by-value language is developed by extending the Hindley-Milner polymorphic type system with recursive types and limited forms of union types. The extension adapts Remy's encoding of record types with subtyping to union types. The encoding yields more compact types and permits more efficient type inference than Cartwright and Fagan's early technique. Correctness proofs are developed by employing a new syntactic app...

Recent trends in programming language implementation are moving more and more towards “managed ” runtime environments. These offer many benefits, including static and dynamic type checking, security, profiling, bounds checking and garbage collection. The Common Language Infrastructure (CLI) is Microsoft’s attempt to define a managed runtime environment. However, since it was designed with more mainstream languages in mind, including C ♯ and C++, CLI proves restrictive when compiling functional languages. More specifically, for compilers such as GHC, which compiles Haskell, the CLI provides little support for lazy evaluation, currying (partial applications) and static type checking. The CLI does not provide any way of representing a computation in an evaluated and non-evaluated form. It does not allow functions to directly manipulate the runtime stack, and it restricts static typing in various forms; including subsumption over function types. In this thesis, we describe a new compilation method that removes the need for runtime argument checks. Runtime argument checking is required to