Dispatch function

From CS 61A Wiki
Jump to: navigation, search

A dispatch function is a function that takes in a message and returns a value accordingly.

The body of a dispatch function is always the same:

  • one conditional statement with several clauses
  • headers perform equality tests on the message

Examples

def cons(a, b):
  def pair(message):
    if message == 'car':
      return a
    else:
      return b
  return pair
def rational(x, y):
    """
    >>> rat = rational(1, 3)
    >>> rat('numer')
    1
    >>> rat('denom')
    3
    """
    def dispatch(field):
        if field == 'numer':
            return x
        elif field == 'denom':
            return y
        else:
            return 'invalid field'
    return dispatch

Sources