Our syntax macros are similar to previous work in that the compiler accepts collections of grammatical rules that extend the syntax in which a subsequent program may be written. Growing (domain-specific) extensions of programming languages. We claim this forms a general abstraction mechanism for We present our experiences with a syntax macro language augmented with a concept of metamorphisms. Guy Steele: Growing a Language, OOPSLA'98 invited talk. "From now on, a main goal in designing a language should be to plan for growth." We explore why the essential problem of locating data in trees is intimately linked with tree automata and decidable logics, somewhat in parallel to the link between query algebras and rst-order logic in relational database theory. In particular, we will contrast conventional concepts of database theory such as relational calculus with that of more procedural notations for trees. Because trees are objects that are very complicated to manipulate directly through pointer updates, declarative techniques are becoming increasingly important, especially when it comes to exploring, mining, and constructing tree-shaped data. We look at techniques now used in practice for dealing with XML trees, and we note how they depart from old-fashioned uses. In this chapter, we shall see that the suspicion is easily dispelled. It performs well in practice and never introduces ambiguities or LR(k) conflicts.ĭdition- ally, trees have been studied intensively in computer science ever since, so we might suspect that the reason for the excitement is simply that practitioners are catching up with methods of abstraction and representation viatrees that are well known in academia. This process can be used as a preprocessing step before other CFG manipulations and is well behaved. The results are then reinterpreted back into CFGs that encode the specified restrictions. We do this by reinterpreting CFGs as tree automata and then intersecting them with tree automata encoding the desired restrictions. In this paper, we show how tree automata can modularly and concisely encode such restrictions. Often, language designers resort to restructuring their grammars in order to encode these restrictions, but this obfuscates the designerâs intent and can make grammars more difficult to read, write, and maintain. However, they are special purpose and do not handle the grammatical restrictions that language designers need in order to resolve ambiguities like dangling else, the interactions between binary operators and functional if expressions in ML, and the interactions between object allocation and function calls in JavaScript. Precedence and associativity declarations in systems like yacc resolve ambiguities in context-free grammars (CFGs) by specifying restrictions on allowed parses.
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This extension of MONA defines the new WSRT logic together with its decision procedure. To obtain a working tool, we have extended MONA to directly support recursive structures using an encoding that provides a necessary state-space factorization.
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A naive generalization to recursive data-types determines an encoding in WS2S that leads to infeasible computations. In that case, programs are translated into WS1S formulas. This extends previous work that uses a similar technique to verify a simpler syntax manipulating only list structures. If a program fails to verify, a counterexample in the form of an initial store that leads to an error is automatically generated. A default well-formedness invariant is supplied and can be strengthened as needed by programmer annotations. This technique is complete for loop-free code, but for loops and recursive functions we rely on Hoare-style invariants. A verified program is guaranteed to preserve the tree-shapes of data structures, to avoid pointer errors such as NULL dereferences, leaking memory, and dangling references, and furthermore to satisfy assertions specified in a specialized store logic.Ī program is transformed into a single formula in WSRT, an extension of WS2S that is decided by the MONA tool. We do not consider the complete behavior of programs, but only attempt to verify that they respect the shape and integrity of the store.
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We exhibit a technique for automatically verifying the safety of simple C programs working on tree-shaped data structures.