An overview of the Leon verification system

Abstract

We present the Leon verification system for a subset of the Scala programming language. Along with several functional features of Scala, Leon supports imperative constructs such as mutations and loops, using a translation into recursive functional form. Both properties and programs in Leon are expressed in terms of user-defined functions. We discuss several techniques that led to an efficient semi-decision procedure for first-order constraints with recursive functions, which is the core solving engine of Leon. We describe a generational unrolling strategy for recursive templates that yields smaller satisfiable formulas and ensures completeness for counterexamples. We illustrate the current capabilities of Leon on a set of examples, such as data structure implementations; we show that Leon successfully finds bugs or proves completeness of pattern matching as well as validity of function postconditions.

Programming with enumerable sets of structures

“…SciFe alleviates the need to write an additional predicate to check the invariant after execution, by employing the enumerator as a structure recognizer. In addition to generating a data structure encoded at a particular index, the enumerator can play the role of an oracle-given a data structure, it answers with true or false, whether the data structure can be generated with the enumerator (and thus also whether it is correct) 3 . We can easily turn our enumerator into an oracle to test insertion without any additional contracts:…”

“…Automated data structure generation techniques are useful in many contexts: software testing [10,11,18,45], synthesis [30,32], bounded and unbounded verification [3,15,25,28], theorem proving [6,12], and others [4,9,22,24,31]. The structures in question are not just the common algorithmic data structures that are the backbone of common libraries, but also domain-specific structures, such as abstract models of programs in compilers, image formats, or DOM trees in browsers.…”

OpenJML: Software verification for Java 7 using JML, OpenJDK, and Eclipse

“…Eiffel [39] built less expressive specifications directly into the programming language. Leon [4] is a verifier for Scala programs. Key [3] and Why3 [24] are other recent tools that apply to Java programs, but require the user to interact with theorem proving tools separately from the software development IDE.…”

Symbolic Resource Bound Inference for Functional Programs

“…To construct verification conditions (VCs) in the presence of algebraic data-types (ADTs) and recursive functions we use the approach employed in the Leon verifier [5,28]. The approach constructs VCs incrementally wherein each increment makes the VC more precise by unrolling the function calls that have not been unrolled in the earlier increments (referred to as VC refinement).…”