integerize contractor and integer solutions

[dpsanders]

Add an integerize contractor as in this code I wrote , discussed in this Discourse post

[cvanaret]

Great idea!

As I mentioned in an email, you can either:

• add the integerize() constraint to the system of constraints (like in your example), in which case the integerize contractor is invoked from time to time ;
• call integerize() in a systematic manner within the generated code of the forward-backward contractor, whenever the range of an integer variable is reduced. This would be the "optimal" way to go to maximize the filtering power. A possibility would be to attach an "integer" tag to a variable upon symbolic definition (e.g. @integer_variables x) and the appropriate code should be generated, for example

begin
(_c, _b, y) = minus_rev(_c, _b, y)
(_b, _a, x) = plus_rev(_b, _a, x)
x = integerize(x)
(_a, x) = exp_rev(_a, x)
x = integerize(x)
end

for the constraint "exp(x) + x - y = 0" with x integer.