Ruby functions vs methods

lambdas in Ruby are objects of class Proc. Proc objects don't belong to any object. They are called without binding them to an object.

Methods are objects of either class Method or UnboundMethod, depending on whether they're bound or unbound. See the explanation here. Unbound methods can't be called until they're bound to an object.

lambda{|x| x}.class      # => Proclambda{|x| x}.call(123)  # => 123class Foo  def bar(baz)    baz  endendputs Foo.new.method(:bar).class     # => Methodputs Foo.new.method(:bar).call(123) # => 123puts Foo.instance_method(:bar).class     # => UnboundMethodputs Foo.instance_method(:bar).call(123) # => throws an exception

You can bind an UnboundMethod to an object and then call it. But you can't bind a Proc to an object at all. Proc objects can however capture local variables in the surrounding scope, becoming closures.

Procs and lambdas are both objects unto themselves, with a call method that actually invokes the block associated with the proc (or lambda). However, Ruby provides some syntactic sugar to invoke them without the explicit call to call.

I think the distinction is between methods and first order function ie. functions that can be passed around as values.