DynamicTypeSet

Finding out, whether any given Eiffel system contains a CAT call is undecidable. A CAT call finding algorithm will thus make one or both of the following error kinds:

• Kind A: Report a system that has no CAT-call as NOT CAT-call free.
• Kind B: Report a system containing CAT-calls as CAT-call free.

An algorithm that makes errors of kind B is of no use. An algorithm that only makes errors of kind A leads to type safety. But too many errors of kind A limit its useless (the trivial algorithm, that reports every Eiffel system as NOT CAT call free makes no errors of Kind B bot is completely useless). The goal is thus to find a subclass of the class of CAT-call free Eiffel systems that

• is decidable
• makes no errors of kind B
• makes only few errors of kind A.

The dynamic type set algorithm

can make two kinds of errors

But it is easy to come up with an algorithm that detects for a subset of all CAT-call free Eiffel systems that they are CAT-call free 
  * detects a subset of all CAT-call free

But for some systems it is easy to show, that they are CAT call free.

The dynamic type set algorithm (DTSA) as defined in ETL2 combined with a system validity check, removes the most serious holes in the Eiffel type system. The challenge is thus to find the So DTSA cannot do that, it will correctly declare some Eiffel systems as CAT call free