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require "spec_helper"
class Machine < Struct.new(:expression, :environment)
def step
self.expression = expression.reduce(environment)
end
def run
while expression.reducible?
puts expression
step
end
puts expression
end
end
class Number < Struct.new(:value)
def reducible?
false
end
def to_s
value.to_s
end
def inspect
"<<#{self}>>"
end
end
class Add < Struct.new(:left, :right)
def reducible?
true
end
def reduce(environment)
if left.reducible?
Add.new(left.reduce(environment), right)
elsif right.reducible?
Add.new(left, right.reduce(environment))
else
Number.new(left.value + right.value)
end
end
def to_s
"(#{left} + #{right})"
end
def inspect
"<<#{self}>>"
end
end
class Multiply < Struct.new(:left, :right)
def reducible?
true
end
def reduce(environment)
if left.reducible?
Multiple.new(left.reduce(environment), right)
elsif right.reducible?
Multiple.new(left, right.reduce(environment))
else
Number.new(left.value * right.value)
end
end
def to_s
"(#{left} * #{right})"
end
def inspect
"<<#{self}>>"
end
end
class Boolean < Struct.new(:value)
def to_s
value.to_s
end
def inspect
"<<#{self}>>"
end
def reducible?
false
end
end
class LessThan < Struct.new(:left, :right)
def to_s
"#{left} < #{right}"
end
def inspect
"<<#{self}>>"
end
def reducible?
true
end
def reduce(environment)
if left.reducible?
LessThan.new(left.reduce(environment), right)
elsif right.reducible?
LessThan.new(left, right.reduce(environment))
else
Boolean.new(left.value < right.value)
end
end
end
class Variable < Struct.new(:name)
def to_s
name.to_s
end
def inspect
"<<#{self}>>"
end
def reducible?
true
end
def reduce(environment)
environment[name]
end
end
describe "expressions" do
it "can do math" do
machine = Machine.new(Add.new(Multiply.new(Number.new(1), Number.new(2)), Multiply.new(Number.new(3), Number.new(4))))
result = machine.run
puts result
end
it "can check less than" do
puts Machine.new(LessThan.new(Number.new(5), Add.new(Number.new(2), Number.new(2)))).run
end
it "can assign variables" do
environment = { x: Number.new(3), y: Number.new(4) }
puts Machine.new(Add.new(Variable.new(:x), Variable.new(:y)), environment).run
end
end
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