The stab operator is named for its resemblance to a knife or stabbing motion: ->. Following the stab portion of the operator, there is a argument list, just as with in a normal method. Then, a normal Ruby block in braces.
Since the lambda's argument list is a formal argument list, as opposed to a block argument list, several other features such as default argument values are supported. A lambda is somewhere in between an anonymous block or closure and a formal named method.
#!/usr/bin/env ruby
# Assign a lambda to a variable
l = ->(x,y){ x * y }
# Then call it with various arguments
puts l.call( 10, 12 )
puts l.call( 14.44, -3.4545 )
puts l.call( "!", 10 )
# Declare a method that takes a callable argument
def call_a_lambda( x, y, l )
puts l.call( x, y )
end
# Declare a lamba in the method invocation
call_a_lambda( 10.0, 12.0, ->(x,y){ x/y } )
# Lambdas have a formal argument list, complete with
# default arguments
l = ->(x,y=10){ x * y }
# Call the new lambda with 1 or 2 arguments
puts l.call(4)
puts l.call('-')
puts l.call(1.44, 23)
