The last years have witnessed a flurry of new results in the area of partial evaluation. These tutorial notes survey the field and present a critical assessment of the state of the art. 1 Introduction Partial evaluation is a source-to-source program transformation technique for specializing programs with respect to parts of their input. In essence, partial evaluation removes layers of interpretation. In the most general sense, an interpreter can be defined as a program whose control flow is determined by its input data. As Abelson points out, [43, Foreword], even programs that are not themselves interpreters have important interpreter-like pieces. These pieces contain both compile-time and run-time constructs. Partial evaluation identifies and eliminates the compile-time constructs. 1.1 A complete example We consider a function producing formatted text. Such functions exist in most programming languages (e.g., format in Lisp and printf in C). Figure 1 displays a formatting functio...

ion. A common form of transformation, which is easily justified by appealing to reversibility, is abstraction. The abstraction transformation lifts some instances of subexpressions from the right-hand sides of a set of definitions and replaces them with function calls for some new functions. The abstraction process can be used in conjunction with a call-by-need implementation to avoid repeated evaluation of subexpressions. A well-known example is Hughes' supercombinator abstraction [Hughes 1982]. Another form of abstraction which is common in program transformation is syntactic generalization in which an expression e is replaced by a function call g e 1 : : : e n , where g is a new function defined by g x 1 : : : xn \Delta = e 0 , such that e j e 0 f e 1 : : : e n= x 1 : : : xn g. General statements about abstractions and their correctness are notationally rather complex. In practice we have found it is easier to appeal to a reversibility argument on a case-by-case basis than...

We introduce a general uniform language-independent framework for designing online and offline source-to-source program transformations by abstract interpretation of program semantics. Iterative source-to-source program transformations are designed constructively by composition of source-to-semantics, semantics-totransformed semantics and semantics-to-source abstractions applied to fixpoint trace semantics. The correctness of the transformations is expressed through observational and performance abstractions. The framework is illustrated on three examples: constant propagation, program specialization by online and offline partial evaluation and static program monitoring.

This paper shows how the Improvement Theorem---a semantic condition

The goal of program transformation is to improve efficiency while preserving meaning. One of the best known transformation techniques is Burstall and Darlington's unfold-fold method. Unfortunately the unfold-fold method itself guarantees neither improvement in efficiency nor total-correctness. The correctness problem for unfold-fold is an instance of a strictly more general problem: transformation by locally equivalence-preserving steps does not necessarily preserve (global) equivalence. This paper presents a condition for the total correctness of transformations on recursive programs, which, for the first time, deals with higher-order functional languages (both strict and non-strict) including lazy data structures. The main technical result is an improvement theorem which says that if the local transformation steps are guided by certain optimisation concerns (a fairly natural condition for a transformation), then correctness of the transformation follows. The improvement theorem make...

An input-output relation for a wide class of program specializers for a simple functional language in the form of Natural Semantics inference rules is presented. It covers polygenetic specialization, which includes deforestation and supercompilation, and generalizes the author’s previous paper on specification of monogenetic specialization like partial evaluation and restricted supercompilation. The specialization relation expresses the idea of what is to be a specialized program, avoiding as much as possible the details of how a specializer builds it. The relation specification follows the principles of Turchin’s supercompilation and captures its main notions: configuration, driving, generalization of a configuration, splitting a configuration, as well as collapsed-jungle driving. It is virtually a formal definition of supercompilation abstracting away the most sophisticated parts of supercompilers— strategies of configuration analysis. Main properties of the program specialization relation—idempotency, transitivity, soundness, completeness, correctness—are formulated and discussed.

Specializing programs with respect to run-time invariants is an optimization technique that has shown to improve the performance of programs substantially. It allows a program to adapt to execution contexts that are valid for a limited time. Run-time specialization is being actively investigated in a variety of areas. For example, recently, major operating system research projects have been focusing on run-time specialization as a means to obtain efficiency from highly extensible and parameterized systems. This paper describes a general approach to run-time specialization. For a given program and a declaration of its runtime invariants, it automatically produces source templates at compile time, and transforms them so that they can be processed by a standard compiler. At run time, only minor operations need to be performed: selecting and copying templates, filling holes with run-time values, and relocating jump targets. As a consequence, run-time specialization is performed very effi...