Reusable named expressions

[bergmanngabor]

We could perhaps have reusable, named expressions:

expression triangle_inequality(A as java.lang.Integer, B as java.lang.Integer, C as java.lang.Integer) {
  A < B+C &&
  B < A+C &&
  C < A+B
} // type inferred as boolean -- or should we make the return type explicit?

Then use them in check expressions (later in evals) directly:

  check triangle_inequality(X,Y,Z);

Perhaps it would be also possible to use them as sub-expressions:

  check (W.endsWith(triangle_inequality(X,Y,Z).toString()));

The advantages I foresee:

• you can reuse the same expression multiple times
  • .eiq code will be more concise, less error-prone
  • only one evaluator class has to be generated for it
  • if pure functional / side effect-free property has to be proven / asserted using annotations / whatever (see #96), you only have to do it once
• if the expression is very complex, you do not have to expand it within the pattern code, making the .eiq tidier, even if you use it only once
• you can include such an expression in a query library! #193
  • in fact, you can generate its evaluator code for the library, and then you can match interpretative queries using this expression with precompiled evaluation (i.e. the stuff that is slow in interpretative mode)!

Priority: low, we do not have user requests for this yet.

[istvanrath]

Moved to Eclipse: https://bugs.eclipse.org/bugs/show_bug.cgi?id=398752