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From: cs450a03@uc780.umd.edu
Newsgroups: comp.lang.misc
Subject: RE: Dynamic typing (part 3)
Message-ID: <13MAR91.00251986@uc780.umd.edu>
Date: 13 Mar 91 00:25:19 GMT
References: <602@optima.cs.arizona.edu> <YR+9VUB@xds13.ferranti.com> <1991Mar13.010946.4536@engage.enet.dec.com>
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The Question, as I understand it, is:
        Is it a "good thing" or a "bad thing" to require programmers
        to specify what types of information can be associated with
        a variable name.

Sample argument for:  Static typing catches errors.
Sample argument against: Static typing encourages errors.

Other argument against: Static typing slows development.
Other argument for: Static typing allows faster code.


Is that the gist of this, so far?
Do I need to add that people favoring dynamic typing also favor dynamic
testing?  Or that existing popular systems (X-windows and emacs come to
mind) are not paragons of efficiency?


My own, biased, observation is that keeping information and control
paths simple goes a long, long way towards catching errors.  Static
typing, as a sort of globalish way of specifying data by side effect
often does little towards simplifying either control or data flow.
The problem being, essentially, that data applicable to function F
may or may not be applicable for function G.  (Or, similarly, datum
X may be used to qualify datum Y, but not datum Z).


For example, consider a function which finds the square of a number.
Nice, simple (almost trivial) function.  Yet on most computers,
you can give it arguments which do not have representable squares.
If you were to solve this problem with static typing, I suppose you
could invent some special numeric type of limited magnitude, and say
that only numbers of that type could be passed to this function.
Does anyone detect a note of insanity here?  Just how are you supposed
to verify that the result of some arbitrary computation, each stage
of which has its own domain (and its own range) will generate results
which are in the domain of the next relation down the line?

You might as well say "Lets find the solution to all problems, rather
than this one problem, because then we'll be more correct."

Yeah, right.

May I humbly suggest, if you really think this (static typing) is a
useful approach, that you spend a little time reviewing completeness
and consistency?  (Ask your favorite mathematician)  Who knows, maybe
you'll be able to solve the knapsack problem.


Finally, to Mr. Grier, who posed the rhetorical problem about trusting
software in critical systems which might have latent bugs:  would you
really trust such software if it had never been tested?  Would it make
you feel safer if each type of data required seperate chunks of code,
with the associated tests and branches and variant storage mechanisms?


This is slightly off the topic of data polymorphism, but I'd like to
point out at work it is considered good form to write code that does
not branch or loop (or use recursion), as much as possible.  Remember,
control flow (such as branching) is just another way of representing
information.  With the proper primitives, you can do an incredible
amount of decision making with zero branching (sort of "super-structured").


Raul Rockwell