By allowing the programmer to write code that can generate code at run-time, meta-programming offers a powerful approach to program construction. For instance, meta-programming can often be employed to enhance program efficiency and facilitate the construction of generic programs. However, meta-programming, especially in an untyped setting, is notoriously error-prone. In this paper, we aim at making meta-programming less error-prone by providing a type system to facilitate the construction of correct meta-programs. We first introduce some code constructors for constructing typeful code representation in which program variables are represented in terms of deBruijn indexes, and then formally demonstrate how such typeful code representation can be used to support meta-programming. With our approach, a particular interesting feature is that code becomes first-class values, which can be inspected as well as executed at run-time. The main contribution of the paper lies in the recognition and then the formalization of a novel approach to typed meta-programming that is practical, general and flexible.

Haskell is a functional programming language whose evaluation is lazy by default. However, Haskell also provides pattern matching facilities which add a modicum of eagerness to its otherwise lazy default evaluation. This mixed or “non-strict” semantics can be quite difficult to reason with. This paper introduces a programming logic, P-logic, which neatly formalizes the mixed evaluation in Haskell pattern-matching as a logic, thereby simplifying the task of specifying and verifying Haskell programs. In p-logic, aspects of demand are reflected or represented within both the predicate language and its model theory, allowing for expressive and comprehensible program verification.

Staging is a programming technique for dividing the computation in order to exploit the early availability of some arguments. In the early stages the program uses the available arguments to generate, at run time, the code for the late stages. A type system for staging should ensure that only well-typed expressions are generated, and that only expressions with no free variables are permitted for evaluation. In this paper, we present a calculus for staged computation in which code from the late stages is composed by splicing smaller code fragments into a larger context, possibly incurring capture of free variables. The type system ensures safety by tracking the names of free variables for each code fragment. The type system is based on the necessity operator □ from constructive modal logic, which we index with a set of names C. Our type □CA classifies expressions of type A that belong to the late stage, and whose free names are in the set C.