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Prevention

rascal-0.34.0
drambiguity-0.2.0

The stash of sentences on the Sentences tab is a valuable source of information, for when a grammar must be fixed, extended or refactored for an outside reason. Next to this all changes to a grammar are causes of new trouble, which is why the Grammar tab offers to save important versions of the grammar over time.

  • Save the stash using the File menu, and to reload the stash with every new version of the grammar.
  • Also save the versions of the grammar in the same go, to compare the semantics of the grammar with older version where necessary.

It is possible (and easy) to run the stashed sentences during continuous integration by calling Dr Ambiguity API functions in a Rascal test function. This way you can use the list of stashed sentences as an important regression test, when someone changes the source code of the underlying grammar.

Regression testing like this goes a long way in preventing ambiguity. The reason is that ambiguity is often introduced into existing grammars by adding more features to a language. The more rules there are, the more possible interactions, the more chance for ambiguity. An early-detection mechanism like the stashed sentences is important.

When such a new ambiguity arises on existing sentences, the Sentence tab with its Use button for each sentence makes it very easy to quickly assess the damage and think about mitigating solutions.