Perhaps the dominant method for building morphological parsers is to use finite state transducer toolkits. The problem with this approach is that finite state transducers require one to think of grammar writing as a programming task, rather than as providing a declarative linguistic description. We have therefore developed a method for representing the morphology and phonology of natural languages in a way which is closer to traditional linguistic descriptions, together with a method for automatically converting these descriptions into parsers, thus allowing the linguistic descriptions to be tested against real language data.
But there is a drawback to this approach: the fact that the descriptive level is different from the implementation level makes debugging of the grammars difficult, and in particular it provides no aid to visualizing the steps in deriving surface forms from underlying forms. We have therefore developed a debugging tool, which allows the linguist to see each intermediate step in the generation of words, without needing to know anything about the finite state implementation. The tool runs in generation mode; that is, the linguist provides an expected parse, and the debugger shows how that underlying form is converted into a surface form given the grammar. (Debugging in the opposite direction—starting from an expected surface form—might seem more natural, but in fact is much harder if that form cannot be parsed, as presumably it cannot be if the grammar needs debugging.)
The tool allows tracing the application of feature checking constraints (important when there is multiple exponence) and phonological rules. It will soon allow viewing the application of suppletive allomorphy constraints, although we describe some theoretical linguistic issues with how the latter should work. The tool can be run from the command line (useful when repeatedly testing the same wordforms while tweaking the grammar), or from a Graphical User Interface (GUI) which prompts the user for the necessary information. The output can be displayed in a browser.
In addition to its use in debugging, the debugger could have an educational use in explicating the forms in a paradigm chart: each cell of the paradigm could be run through the debugger to produce the cell’s derivation, showing how forms which might seem counter-intuitive or irregular are derived. We have not yet implemented this.
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