Posted by Piers Cawley
Sat, 20 Jan 2007 14:58:00 GMT
Your mission, should you choose to accept it, is to explain what the following code does:
<pre>
class Amb
def initialize
@error = Exception.new("Ran out of possibilities")
@failure_continuation = lambda {|v| @error}
end
def assert(assertion)
if !assertion
self.fail
end
end
def deny(assertion)
assert !assertion
end
def fail
@failure_continuation.call(nil)
end
def maybe
one_of [true, false]
end
def one_of(collection = [])
k_prev = @failure_continuation
callcc do |k_entry|
collection.each do |item|
callcc do |k_next|
@failure_continuation = lambda do |v|
@failure_continuation = k_prev
k_next.call(v)
end
k_entry.call(item)
end
end
result = k_prev.call(nil)
if result == @error
raise @error.message
end
end
end
def all_values(&a_block)
k_prev = @failure_continuation
results = []
callcc do |k_retry|
@failure_continuation = lambda {|v| k_retry.call(false)}
results << a_block.call
k_retry.call(true)
end && fail
@failure_continuation = k_prev
results
end
end
Easy? Now explain how it does it.
