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Rascal Pascal Standard ML
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An experiment in type checker generation. Warning: work in progress!

From the user perspective the basic idea is as follows:

  1. Start with a Rascal grammar of the language of interest, say, MiniML.
  2. Write functions for specific language constructs
    • define captures all defining occurrences of variables and their scopes;
    • use captures all uses of variables;
    • require captures all static requirements on the use of certain constructs, such formal/actual parameter correspondence and the like;
    • calculate to compute a type for a language fragment using earlier calculated types, think of the result type of an operator based on its argument types.
  3. The above functions will populate a fact/requirement model (or TModel for short) of a source program to be type checked.
  4. Apply the collect function to a parsed program (a parse tree). This will apply define/use/require/calculate to all relevant places in the tree, will create scopes and use/def information and will also build a collection of constraints. They are all part of the TModel.
  5. Apply solve to the TModel resulting from the previous step. solve is happy if all constraints can be solved and generates error messages otherwise. solve also enhances the original TModel with derived facts that can be used for use/def analysis, interactive display of type information, and the like.
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