Building custom static checkers using declarative programming

Programmers have developed a wide range of tools for sanity checking their code. Compilers perform type checking and generate warnings about undefined or unused variables. Programs such as Microsoft’s FxCop can detect opportunities for optimization, likely bugs such as files that are opened but never closed, and the use of unlocalized strings. These are all examples of static checking, as opposed to dynamic checks (such as assertions) that can only verify behavior for a particular run of the program.