Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!udel!ee.udel.edu
From: new@ee.udel.edu (Darren New)
Newsgroups: comp.lang.misc
Subject: Re: Dynamic typing (part 3)
Message-ID: <50085@nigel.ee.udel.edu>
Date: 8 Apr 91 19:32:12 GMT
References: <28924@dime.cs.umass.edu> <6APR91.10183202@uc780.umd.edu> <6APR91.10374005@uc780.umd.edu>
Sender: usenet@ee.udel.edu
Organization: University of Delaware
Lines: 37
Nntp-Posting-Host: snow-white.ee.udel.edu

In article <6APR91.10374005@uc780.umd.edu> cs450a03@uc780.umd.edu writes:
>I wrote (paraphrasing Darren New)
>>"Dynamic typing is when the type of a variable _may_ be unknown at
>>compile time."

Actually, unless you are talking about type inferencing, I would say
"*must* be unknown."  If the type is known at compile time, it is
static typing, period.  If you don't specify the type but the compiler
can figure it out for you, then that is static typing, because the
type of the values assigned to the variable is known statically.

I never intended to imply that dynamic typing and static typing
cannot be mixed in the same language.

>An even yet more exactly stated version would be :-)
>"Dynamic typing is when the most efficient of the available primitive
>machine representation for some value(s) is chosen at run-time."

I don't think it has anything to do with machine representations or
efficiency.  Your definition would exclude Objective-C, Smalltalk, C++,
and every other dynamically typed language I know except APL.  For
example, Smalltalk does not chose the most efficient version of the
data: it uses what the programmer defines.  Maybe languages like
Mathematica or ML do such a thing, but chosing an efficient
representation is orthagonal to dynamic typing.  For example, in Ada
(as I understand it), one can say "I need a float with this range and
that accuracy at least" and the compiler will chose the most efficient
representation.  In Smalltalk, one must define all the operations on
lists. Ada choses efficient reps but is statically typed, and Smalltalk
does not chose efficient reps but is dynamically typed.

           -- Darren
-- 
--- Darren New --- Grad Student --- CIS --- Univ. of Delaware ---
----- Network Protocols, Graphics, Programming Languages, FDTs -----
  +=+=+ My time is very valuable, but unfortunately only to me +=+=+
+ When you drive screws with a hammer, screwdrivers are unrecognisable +