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Tail optimized recursive call w/ Nathan at Rubyconf
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$depth = 0 | |
at_exit { p depth: $depth } | |
def record_depth | |
$depth = caller.length-1 if caller.length-1 > $depth | |
end | |
require 'binding_of_caller' | |
module Torc | |
def torc(*args) | |
return [:torc, args] if instance_variable_defined? :@caller | |
begin | |
@caller = binding.of_caller(1).eval('__method__') | |
caller_args = [:start, args] | |
loop do | |
caller_args = __send__ @caller, *caller_args.last | |
return caller_args unless caller_args.respond_to? :first | |
return caller_args unless caller_args.first == :torc | |
end | |
ensure | |
remove_instance_variable :@caller | |
end | |
end | |
end | |
def factorial(n) | |
factorial_helper(1, n) | |
end | |
extend Torc | |
def factorial_helper(acc, n) | |
record_depth | |
return acc if n <= 1 | |
torc acc * n, n - 1 | |
end | |
factorial 1 # => 1 | |
factorial 2 # => 2 | |
factorial 3 # => 6 | |
factorial 4 # => 24 | |
factorial 5 # => 120 | |
factorial 6 # => 720 | |
factorial 100 # => 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000 | |
# >> {:depth=>6} |
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