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 that 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:
The partial evaluator transforms
by precomputing all static input at compile time.
The act of partial evaluation is said to "residualize"
A particularly interesting example of the use of partial evaluation, first described in the 1970s by Yoshihiko Futamura,[1] is when prog is an interpreter for a programming language.
If Istatic is source code designed to run inside that 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.