Partial evaluation

In computing, partial evaluation is a technique for several different types of program optimization by specialization. The most straightforward application is to produce new programs which run faster than the originals while being guaranteed to behave in the same way. In computing, partial evaluation is a technique for several different types of program optimization by specialization. The most straightforward application is to produce new programs which run faster than the originals while being guaranteed to behave in the same way. A computer program, prog, is seen as a mapping of input data into output data: I s t a t i c {displaystyle I_{static}} , the static data, is the part of the input data known at compile time. The partial evaluator transforms ⟨ p r o g , I s t a t i c ⟩ {displaystyle langle prog,I_{static} angle } into p r o g ∗ : I d y n a m i c → O {displaystyle prog^{*}:I_{dynamic} o O} by precomputing all static input at compile time. p r o g ∗ {displaystyle prog^{*}} is called the 'residual program' and should run more efficiently than the original program. The act of partial evaluation is said to 'residualize' p r o g {displaystyle prog} to p r o g ∗ {displaystyle prog^{*}} . A particularly interesting example of the use of partial evaluation, first described in the 1970s by Yoshihiko Futamura, is when prog is an interpreter for a programming language. If Istatic is source code designed to run inside said interpreter, then partial evaluation of the interpreter with respect to this data/program produces prog*, a version of the interpreter that only runs that source code, is written in the implementation language of the interpreter, does not require the source code to be resupplied, and runs faster than the original combination of the interpreter and the source. In this case prog* is effectively a compiled version of Istatic.