Ruby: Is something like anonymous function?

Question

In JavaScript I can do something like that:

var foo = function(){
  var a = 5;
  a = a*a;
  return a;
}();

So I can define anonymous function I will use only once. I was trying but my approach is wrong:

foo = {
  a = 5
  a = a*a
  return a
}
#=> SyntaxError: unexpected '\n'...

foo = do
  a = 5
  a = a*a
  a
end
#=> SyntaxError: unexpected keyword_do_block...

foo = {
  a = 5
  a = a*a
  a
}()
#=> SyntaxError: unexpected '\n'...

Answer 1

Well, you could use in Ruby lambda

foo = ->(a) { a * a }
foo.call(4) # => 16

Proc objects are blocks of code that have been bound to a set of local variables. Once bound, the code may be called in different contexts and still access those variables.

Read this When to use lambda, when to use Proc.new?.