Path: utzoo!utgpu!watserv1!watmath!att!ima!esegue!compilers-sender
From: wright@gefion.rice.edu (Andrew Wright)
Newsgroups: comp.compilers
Subject: Re: Defining polymorphism vs. overloading
Keywords: design, polymorphism
Message-ID: <1990Sep2.220039.4966@rice.edu>
Date: 2 Sep 90 22:00:39 GMT
References: <9008310419.AA06194@karakorum.berkeley.edu>
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Reply-To: wright@gefion.rice.edu (Andrew Wright)
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In article <9008310419.AA06194@karakorum.berkeley.edu> oliver@karakorum.berkeley.edu (Oliver Sharp) writes:
>  o  Overloading means using the same name (or symbol) to invoke different
>    code depending on the types of the arguments (or operands).  So, an example
>   ...
>  o  Polymorphism means using the same piece of code to operate on objects of
>    different types.  In LISP, cons is polymorphic because you can give it
>    arguments of different types but it goes ahead and does its thing without
>    worrying about it.

C. Strachey originated the terms "ad-hoc" and "universal" polymorphism
to distinguish these issues.  overloading is an example of ad-hoc polymorphism,
automatic coercions such as real->int are another.
ML is the best example of universal polymorphism (what you call simply
polymorphism above).  See:
@article{Cardelli86,
 author =  "Luca Cardelli and Peter Wegner",
 year =    "1985",
 month =   "December",
 journal = "ACM Computing Surveys",
 volume =  "17",
 number =  "4",
 pages =   "471-522",
 title =   "On Understanding Types, Data Abstraction, and Polymorphism"
}
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