Search-based Program Synthesis

Writing programs that are both correct and efficient is challenging. A potential solution lies in program synthesis aimed at automatic derivation of an executable implementation (the “how”) from a high-level logical specification of the desired input-to-output behavior (the “what”). A mature synthesis technology can have a transformative impact on programmer productivity by liberating the programmer from low-level coding details. For instance, for the classical computational problem of sorting a list of numbers, the programmer has to simply specify that given an input array A of n numbers, compute an output array B consisting of exactly the same numbers as A such that B[i] ≤ B[i + 1] for 1 ≤ i < n, leaving it to th synthesizer to figure out the sequence of steps needed for the desired computation. Traditionally, program synthesis is formalized as a problem in deductive theorem proving:¹⁷ A program is derived from the constructive proof of the theorem that states that for all inputs, there exists an output, such that the desired correctness specification holds. Building automated and scalable tools to solve this problem has proved to be difficult. A recent alternative to formalizing synthesis allows the programmer to supplement the logical specification with a syntactic template that constrains the space of allowed implementations and the solution strategies focus on search algorithms for efficiently exploring this space. The resulting search-based program synthesis paradigm is emerging as an enabling technology for both designing more intuitive programming notations and aggressive program optimizations.