Extracting a formally verified, fully executable compiler from a proof assistant

Compilers that have been formally verified in theorem provers are often not directly usable because the formalization language is not a general-purpose programming language or the formalization contains non-executable constructs. This paper takes a comprehensive, even though simplified model of Java, formalized in the Isabelle proof assistant, as starting point and shows how core functions in the translation process (type checking and compilation) are defined and proved correct. From these, Isabelle's program extraction facility generates ML code that can be directly interfaced with other, possibly “unsafe” code.