A Pattern Logic for Prompt Lazy Assertions in Haskell

Assertions test expected properties of run-time values without disrupting the normal computation of a program. Here we present a library for enriching programs in the lazy language Haskell with assertions. Expected properties are written in an expressive pattern logic that combines pattern matching with logical operations and predicates. The presented assertions are lazy: they do not force evaluation but only examine what is evaluated by other parts of the program. They are also prompt: assertion failure is reported as early as possible, before a faulty value is used by the main computation

Executable Refinement Types

This dissertation introduces executable refinement types, which refine structural types by semi-decidable predicates, and establishes their metatheory and accompanying implementation techniques. These results are useful for undecidable type systems in general. Particular contributions include: (1) Type soundness and a logical relation for extensional equivalence for executable refinement types (though type checking is undecidable); (2) hybrid type checking for executable refinement types, which blends static and dynamic checks in a novel way, in some sense performing better statically than any decidable approximation; (3) a type reconstruction algorithm - reconstruction is decidable even though type checking is not, when suitably redefined to apply to undecidable type systems; (4) a novel use of existential types with dependent types to ensure that the language of logical formulae is closed under type checking (5) a prototype implementation, Sage, of executable refinement types such that all dynamic errors are communicated back to the compiler and are thenceforth static errors.Comment: Ph.D. dissertation. Accepted by the University of California, Santa Cruz, in March 2014. 278 pages (295 including frontmatter