MINERVA provides advanced functionality for constraint handling together with the possibility to add your own user defined constraint handling.

Constraint handling is very powerful e.g. for difficult management problems: resource allocation, scheduling, planning.

MINERVA defines 2 predicates for constraint handling:

        co_add(+Var, +Constraint)
        co_get(+Var, -Constraint)

        co_merge(+Var, +ConstraintList)
        co_check(+Term, +Constraint)

co_add(+Var, +Constraint)

Add a constraint to a variable or constraint variable. "Constraint" can be any term but not a variable.

If "Var" is a variable, then it becomes a constraint variable.

If "Var" is a constraintvariable, then the constraint becomes marked as additional constraint and the user defined predicate co_merge(+Var,[NewConstraint,OldConstraint]) is invoked.

If "Var" is not a variable, then the user defined predicate co_check(+Var, NewConstraint) is invoked.

co_get(+Var, -Constraint)

co_get(+Var, -Constraint) returns the current constraint associated with a constraint variable. If "Var" is not a constraint variable, then the predicate fails.

co_merge(+Var, +ConstraintList)

When constraint variables are unified, then their associated constraints also have to be unified. This is the job of co_merge/2. The list of individual constraints must be combined into a new constraint, which can then be again associated with the constraint variable with co_add/2. If the individual constraints cause a contradiction, then the predicate shall fail.

Before co_merge/2 is invoked, the associated constraint variable is turned into a normal variable. Only after the following invokation of co_add/2 and of course upon backtracking it becomes a constraint variable again.

co_check(+Term, +Constraint)

The user defined predicate co_check/2 is invoked when a constraint variable is instantiated, i.e. bound to a term which is not a variable. co_check/2 must only succeed if this binding is allowed under the given Constraint "Constraint".

Examples

Standard

co_add/2
co_get/2
co_merge/2
co_check/2

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