Comparing lambdas in ruby

2008-11-03T08:54:00Z

to_ruby is a really convenient way to compare the equality of two lambdas. It’s a bit slow though. If we get our hands dirty (only a little!) with ParseTree, we can get a result 2 orders of magnitude quicker. I’d be interested to see if these benchmarks differ significantly on other versions of ruby.

12	~ $ ruby -vruby 1.8.6 (2007-09-23 patchlevel 110) [i686-darwin8.11.1]

require 'benchmark'
require 'parse_tree'
require 'ruby2ruby'

def gen_lambda
  lambda {|x| x + 1 }
end

Parser = ParseTree.new(false)

# This only requires parse tree, not ruby2ruby
def proc_identity(block)
  klass = Class.new
  name = "myproc"
  klass.send(:define_method, name, &block)

  # .last ignores the method name and definition - they're irrelevant
  Parser.parse_tree_for_method(klass, name).last 
end

n = 1000
Benchmark.bmbm do |x|
  x.report("#to_ruby") { n.times { gen_lambda.to_ruby == gen_lambda.to_ruby }}
  x.report("#to_sexp") { n.times { gen_lambda.to_sexp == gen_lambda.to_sexp }}
  x.report("manual")   { n.times { proc_identity(gen_lambda) == proc_identity(gen_lambda) }}
end

1234	user system total real#to_ruby 4.460000 0.220000 4.680000 ( 4.695327)#to_sexp 0.920000 0.190000 1.110000 ( 1.110214)manual 0.030000 0.000000 0.030000 ( 0.032768)

In case you were wondering, I was playing around with this while implementing unique data generation for dm-sweatshop

Lambda - Xavier Shay's Blog

Comparing lambdas in ruby