index.rb

require 'durable'

Durable.ruleset :circle do
  when_all(
    c.point = (+m.x) & (+m.y),
    c.circle = m.radius_squared == ( point.x * point.x ) + ( point.y * point.y )
  ) do
    puts "point (#{point.x}, #{point.y}) " \
      "is on the edge of circle #{circle.name}"
  end
  when_all(
    c.point = (+m.x) & (+m.y),
    c.circle = m.radius_squared < ( point.x * point.x ) + ( point.y * point.y )
  ) do
    puts "point (#{point.x}, #{point.y}) " \
      "is outside of circle #{circle.name}"
  end
  when_all(
    c.point = (+m.x) & (+m.y),
    c.circle = m.radius_squared > ( point.x * point.x ) + ( point.y * point.y )
  ) do
    puts "point (#{point.x}, #{point.y}) " \
      "is inside of circle #{circle.name}"
  end
end

Durable.assert :circle, {name: :a, radius_squared: 25, x: 0, y: 0}
Durable.assert :circle, {x: 0, y: 0}
Durable.assert :circle, {x: 1, y: 1}
Durable.assert :circle, {x: -1, y: -1}
Durable.assert :circle, {x: 5, y: -5}
Durable.assert :circle, {x: 5, y: 0}
Durable.assert :circle, {x: 0, y: 5}
Durable.assert :circle, {x: 2, y: 2}
Durable.assert :circle, {x: 3, y: 3}

output

$ ruby index.rb
point (0, 0) is inside of circle a
point (1, 1) is inside of circle a
point (-1, -1) is inside of circle a
point (5, -5) is outside of circle a
point (5, 0) is on the edge of circle a
point (0, 5) is on the edge of circle a
point (2, 2) is inside of circle a
point (3, 3) is inside of circle a