A system for assisting in the testing phase of compilers is described. The definition of the language to be compiled drives an automatic sentence generator. The language is described by an extended BNF grammar which can be augmented by actions to ensure contextual congruence, e.g. between definition and use of identifiers. For deep control of the structure of the produced sample the grammar can be described by step-wise refinements: the generator is iteratively applied to each level of refinement, producing at last compilable, complete programs. The implementation is described and some experimental results are reported concerning PLZ, MINIPL and some other languages

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This paper is concerned with a formal model for data structure definition: data graph grammars (DGG's). The model is claimed to give a rigorous documentation of data structures and to suit very properly program design via stepwise refinement. Moreover it is possible to verify data structure correctness, with regard to their formal definition. Last, attribute context-free data graph grammars (A-CF-DSG's) are intr~ duced. A-CF-DGG's not only give a complete and clean description of d~ ta structures and algorithms running along data structures, but also can support an automatic synthesis of such algorithms.

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