Tsifter

Types

• Problem: immutable sets of variables and constraints
  • bool IsSatisfiedBy(Assignment a)
• Assignment: assignment of values to the variables of a problem. considered partial if not all variables of the problem are assigned.
  • wrapper for an ImmutableDictionary<IVariable, object>
  • object this[IVariable variable]
  • T Read(IVariable variable)
  • Assignment Rebuild(Func<Dict<IVariable, object>, Dict<IVariable, object>> map)
• Solution: immutable structure with a Problem and an Assignment that satisfies its constraints.
  • Problem
  • Assignment
  • constructor fails if assignment is partial or doesnt satisfy the problem.
• ProblemBuilder: Configures and assembles a Problem.
  • public HashSet Variables
  • public HashSet Constraints
  • IVariable AddVariable(IEnumerable domain, string? name)
  • IConstraint AddConstraint(ITerm term)
  • Problem Build()
• IVariable<T>: has an IEnumerable as representation of its domain
  • Type ValueType { get; }
  • IEnumerable Domain { get; }
• IConstraint: Computation on variables producing a boolean, implements ITerm
  • bool IsSatisfiedBy(Problem p, Assignment a)
• ITerm<T>: Computation on variables
  • List Scope { get; }
  • T Evaluate(Problem p, Assignment a)
• AC3Solver: implementation of the AC3 algorithm supporting only binary constraints (terms with a scope containing 2 variables)
  • IEnumerable Solutions()
  • Solution? FirstOrDefault()

Simple Example

using csp;

class Program {
	public static void Main(string[] args) {
		var prob = new ProblemBuilder();
		var a = prob.AddVariable<int>(Enumerable.Range(1,5), "A");
		var b = prob.AddVariable<int>(Enumerable.Range(1,5), "B");

		var constraint = prob.AddConstraint(new EqConstraint<int>(a,b));
		// using linq: prob.AddConstraint(
		//		(from i in a from j in b select i != j)
		//			.SetScope(a,b)
		//  )

		var problem = prob.Build();

		var solver = new AC3Solver();

		foreach (var solution in solver.Solutions())
			Console.WriteLine(solution.Assignment.ToString());
	}
}