class Prism::ProgramNode

def ===(other)

comparing the value of locations. Locations are checked only for presence.
Implements case-equality for the node. This is effectively == but without 
def ===(other)
  other.is_a?(ProgramNode) &&
    (locals.length == other.locals.length) &&
    locals.zip(other.locals).all? { |left, right| left === right } &&
    (statements === other.statements)
end