polymorphism

polymorphism
    n 1: (genetics) the genetic variation within a population that
         natural selection can operate on
    2: (chemistry) the existence of different kinds of crystal of
       the same chemical compound [syn: {polymorphism},
       {pleomorphism}]
    3: (biology) the existence of two or more forms of individuals
       within the same animal species (independent of sex
       differences)
    

Polymorphism \Pol`y*mor"phism\, n.
   1. (Crystallog.) Same as {Pleomorphism}.
      [1913 Webster]

   2. (Biol.)
      (a) The capability of assuming different forms; the
          capability of widely varying in form.
      (b) Existence in many forms; the coexistence, in the same
          locality, of two or more distinct forms independent of
          sex, not connected by intermediate gradations, but
          produced from common parents.
          [1913 Webster]
    

polymorphism
parametric polymorphism
polymorphic

   <theory, programming> A concept first identified by
   {Christopher Strachey} (1967) and developed by Hindley and
   Milner, allowing {types} such as list of anything.  E.g. in
   {Haskell}:

   	length :: [a] -> Int

   is a function which operates on a list of objects of any type,
   a (a is a {type variable}).  This is known as parametric
   polymorphism.  Polymorphic typing allows strong type checking
   as well as generic functions.  {ML} in 1976 was the first
   language with polymorphic typing.

   Ad-hoc polymorphism (better described as {overloading}) is the
   ability to use the same syntax for objects of different types,
   e.g. "+" for addition of reals and integers or "-" for unary
   negation or diadic subtraction.  Parametric polymorphism
   allows the same object code for a function to handle arguments
   of many types but overloading only reuses syntax and requires
   different code to handle different types.

   See also {generic type variable}.

   In {object-oriented programming}, the term is used to describe
   a {variable} that may refer to objects whose {class} is not
   known at {compile time} and which respond at {run time}
   according to the actual class of the object to which they
   refer.

   (2002-08-08)