Comment 0 for bug 672227

Currently during the evaluation of expressions, the built in functions raise an exception
when code should be generated. This creates problems with the idea that compilation is really
interpretation of the program with code generation as a side effect. (Bug #597234 )

* A possible idea is to return unknown values instead of raising an exception.
* The value would be directly optimized away by the expression code.
* It would make functions that return objects of multiple types possible; but are those
  functions desired?

Problems:
* Functions that return NONE must have a way to request that code is generated.

* Assignments must be performed differently (they can't return an unknown value), but they
  are performed differently currently too.

See also:
Bug #597234