Arity raiser and its use in program specialization

Abstract

Experiments on generating compilers by specializing specializers with respect to interpreters have shown that the compilers thus obtained have a natural structure only if the specializer does variable splitting. Variable splitting can result in a residual program using several variables to represent the values of a single variable of the original program. In the case of functional programming variable splitting is done by raising the arities of functions. The paper describes the structure and principles of operation of an arity raiser dealing with programs in a subset of pure Lisp.Keywords: arity raiser, compiler generator, partial evaluation, retyping, specializer, variable splitting. I NTRODUCTI ONProgram specialization [Dixon 711 seems to be a promising and powerful technique that can lead to new program development methodology.By program special iza t ion we understand constructing, when given a "general-purpose" program and some restriction on its usage, a more efficient "specialized" residual program. Being optimized and simplified version of the original program, the residual program, however, must be equivalent to the original one when used according to the restriction.By specializer we understand a system that, given a program and a restriction, will produce a specialized version of the original program. control restructuring and data retyping (i.e. changing representation of data).As far as the control restructuring is concerned, various

Evolution of partial evaluators: Removing inherited limits

“…We noted that the limit on number of parameters has been handled di erently, b y a post-process, e.g. in Romanenko 1990. Similarly, it is possible that limits on types and constructors can be handled by post processing.…”

“…This is true also for partially static structures, and was indeed one of the original motivations for introducing these. This may h a ve been a major reason for the success of this approach o ver arity raising Romanenko 1990, which only solves the variable splitting problem, and bifurcation Mogensen 1989, De Neil et al 1990, which only solves the binding time improvement aspect.…”

Partial evaluation and separate compilation

“…For example, Romanenko's arity raising [Rom90] allows one parameter in the source program to give rise to many in the residual program -without it, 'compiled code' was obliged to pass multiple parameters in one list. Mogensen's constructor specialisation [Mog93] allows one constructor in the source to give rise to many in the residual code -without it, 'compiled code' had to represent different constructors by one with a 'constructor name' component.…”

Avoiding repeated tests in pattern matching

“…In the literature arity raising is applied to replacing an argument pair by two single arguments (cf. [8]) whereas we employ a conditional arity raising. Only if it is known that some argument is a constructor term with a certain top constructor we supply the arguments of the constructor in place of the term as arguments to the function.…”

“…We make the distinction by underlining the generated program text. Romanenko deals with arity raising in the context of partial evaluation and program specialization [8]. He discusses the structure and principles of operation of an arity raiser in the context of a subset of pure Lisp.…”