... intermediate language and dynamic execution environment for the implementation and inter-operation of multiplesource languages. In this paper we extend it with direct support for parametric polymorphism (also known as generics), describing thedesign through examples written in an extended version of the C# programming language, and explaining aspects of implementationby reference to a prototype extension to the runtime. Our design is very expressive, supporting parameterized types,polymorphic static, instance and virtual methods, "F-bounded " type parameters, instantiation at pointer and value types, polymor-phic recursion, and exact run-time types. The implementation takes advantage of the dynamic nature of the runtime, performing just-in-time type specialization, representation-based code sharing and novel techniques for efficient creation and use of run-time types.Early performance results are encouraging and suggest that programmers will not need to pay an overhead for using generics,achieving performance almost matching hand-specialized code.

We describe a design pattern for writing programs that traverse data structures built from rich mutually-recursive data types. Such programs often have a great deal of "boilerplate" code that simply walks the structure, hiding a small amount of "real" code that constitutes the reason for the traversal. Our technique allows most...

Compilers for monomorphic languages, such as C and Pascal, take advantage of types to determine data representations, alignment, calling conventions, and register selection. However, these languages lack important features including polymorphism, abstract datatypes, and garbage collection. In contrast, modern programming languages such as Standard ML (SML), provide all of these features, but existing implementations fail to take full advantage of types. The result is that performance of SML code is quite bad when compared to C. In this thesis, I provide a general framework, called type-directed compilation, that allows compiler writers to take advantage of types at all stages in compilation. In the framework, types are used not only to determine efficient representations and calling conventions, but also to prove the correctness of the compiler. A key property of typedirected compilation is that all but the lowest levels of the compiler use typed intermediate languages. An advantage of this approach is that it provides a means for automatically checking the integrity of the resulting code. An important

This paper describes CCured, a program transformation system that adds type safety guarantees to existing C programs. CCured attempts to verify statically that memory errors cannot occur, and it inserts run-time checks where static verification is insu#cient

Phantom types are data types with type constraints associated with dierent cases. Examples of phantom types include typed type representations and typed higher-order abstract syntax trees. These types can be used to support typed generic functions, dynamic typing, and staged compilation in higher-order, statically typed languages such as Haskell or Standard ML. In our system, type constraints can be equations between type constructors as well as type functions of higher-order kinds. We prove type soundness and decidability for a Haskell-like language extended by phantom types.

Most specifications of garbage collectors concentrate on the low-level algorithmic details of how to find and preserve accessible objects. Often, they focus on bit-level manipulations such as "scanning stack frames," "marking objects," "tagging data," etc. While these details are important in some contexts, they often obscure the more fundamental aspects of memory management: what objects are garbage and why? We develop a series of calculi that are just low-level enough that we can express allocation and garbage collection, yet are sufficiently abstract that we may formally prove the correctness of various memory management strategies. By making the heap of a program syntactically apparent, we can specify memory actions as rewriting rules that allocate values on the heap and automatically dereference pointers to such objects when needed. This formulation permits the specification of garbage collection as a relation that removes portions of the heap without affecting the outcome of the evaluation. Our high-level approach allows us to specify in a compact manner a wide variety of memory management techniques, including standard trace-based garbage collection (i.e., the family of copying and mark/sweep collection algorithms), generational collection, and type-based, tag-free collection. Furthermore, since the definition of garbage is based on the semantics of the underlying language instead of the conservative approximation of inaccessibility, we are able to specify and prove the idea that type inference can be used to collect some objects that are accessible but never used.

The FLINT project at Yale aims to build a state-of-the-art systems environment for modern typesafe languages. One important component of the FLINT system is a high-performance type-directed compiler for SML'97 (extended with higher-order modules). The FLINT/ML compiler provides several new capabilities that are not available in other type-based compilers: ffl type-directed compilation is carried over across the higher-order module boundaries; ffl recursive and mutable data objects can use unboxed representations without incurring expensive runtime cost on heavily polymorphic code; ffl parameterized modules (functors) can be selectively specialized, just as normal polymorphic functions; ffl new type representations are used to reduce the cost of type manipulation thus the compilation time. This paper gives an overview of these novel aspects, and a preliminary report on the current status of the implementation. 1 Introduction The FLINT project at Yale aims to build a state-of-the-ar...

Certified code is a general mechanism for enforcing security properties. In this paradigm, untrusted mobile code carries annotations that allow a host to verify its trustworthiness. Before running the agent, the host checks the annotations and proves that they imply the host's security policy. Despite the flexibility of this scheme, so far, compilers that generate certified code have focused on simple type safety properties rather than more general security properties.

A certified binary is a value together with a proof that the value satisfies a given specification. Existing compilers that generate certified code have focused on simple memory and control-flow safety rather than more advanced properties. In this paper, we present a general framework for explicitly representing complex propositions and proofs in typed intermediate and assembly languages. The new framework allows us to reason about certified programs that involve effects while still maintaining decidable typechecking. We show how to integrate an entire proof system (the calculus of inductive constructions) into a compiler intermediate language and how the intermediate language can undergo complex transformations (CPS and closure conversion) while preserving proofs represented in the type system. Our work provides a foundation for the process of automatically generating certified binaries in a type-theoretic framework. 1

Run-time type dispatch enables a variety of advanced optimization techniques for polymorphic languages, including tag-free garbage collection, unboxed function arguments, and flattened data structures. However, modern type-preserving compilers transform types between stages of compilation, making type dispatch prohibitively complex at low levels of typed compilation. It is crucial therefore for type analysis at these low levels to refer to the types of previous stages. Unfortunately, no current intermediate language supports this facility. To fill this gap, we present the language LX, which provides a rich language of type constructors supporting type analysis (possibly of previous-stage types) as a programming idiom. This language is quite flexible, supporting a variety of other applications such as analysis of quantified types, analysis with incomplete type information, and type classes. We also show that LX is compatible with a type-erasure semantics. 1 Introduction Type-directed co...