This is a reimplementation of the integer variable detection procedure.
The idea is to iteratively assume variables to be noninteger, and to
prove that this would lead to a false or erroneous result. If the proof
is successful, the variable is integer as a consequence.
With this change, domains detected for predicate parameters are properly
propagated to all occurences of the respective variables, enabling more
integer simplifications.
This adds a new syntax for declaring functions integer:
#external integer(<function name>(<arity)).
If a function is declared integer, it may enable some variables to be
detected as integer as well.
For clarity, this moves the Domain enum class to a separate header,
because it’s not just variable-specific but also applicable to
functions, for example.
This adds initial support for detecting integer variables in formulas.
The scope is somewhat limited in that variables matching predicate
parameters with known integer type aren’t propagated to be integer as
well yet. Also, the use of constants and functions prevents variables
from being detected as integer, because they have to be assumed to be
externally defined in such a way that they evaluate to general values
and not necessarily integers.
Patrick Lühne