Whatnot

Whatnot is a Ruby wrapper for the Minisat CSP solver with flexible constraint definition syntax.

Motivation

I looked at the existing tools for constraint-solving in Ruby and found that they were either: (a) too slow to handle highly complex systems of constraints, or (b) too inflexible to support all but the most well-known types of problems. So I wanted to provide a tool that was both flexible and fast.

Concepts

To define a constraint problem, you can create two types of variables:

1. A slot: a variable that can only hold one value in an array of possible values.
2. A set: a variable that can hold one or more of an array of values.

Then you may specify any number of constraints between any number of variables.

Syntax

Initializing

First, you have to create a SwitchInterpreter:

i = SwitchInterpreter.new

Creating variables

To create a slot called :B which can either hold 1 or 2:

i.create_slot(:B, [1,2])

To create a set called :C which can hold up to 3 values between 1 and 6:

i.create_set(:C, [1,2,3,4,5,6], max_values: 3)

Creating constraints

To create a constraint that all values of C should be greater than B:

i.create_constraint(:C, :B) { |**sol| sol[:C].all? { |c| c > sol[:B] } }

Installing

Minisat must be installed. On a Mac:

$ brew install gcc
$ brew install minisat