| 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)
The programmer is has to supply two user defined predicates:
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
For examples please refer to the section ExamplePrograms.
Standard
These predicates are not part of the ISO-Prolog Standard.
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