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Static typing disciplines


Greg,

>And of course any static typing discipline will be 
>incomplete.  This does not make them unattractive or
>useless, rather a hard area that must carefully balance
>user-interface, technical, and esthetic issues (what kinds 
>of type information will programmers write, what can be 
>inferred, what kinds of error messages make sense,
>how is programming methodology influenced, what are
>resaonable notions of "bad", etc.)  And
>this is why it's been such an active area of research
>for the past 10-15 years (as opposed to S-expressions.)

I agree.  But note that your opening sentence really is
a paraphrase of Matthias's critique of Milner's seminal paper on
ML "type safety".  If static typing disciplines are incomplete, then

    Well-typed programs CAN go wrong!

Static typing systems only rule out a particular subset of run-time
errors.  More sophisticated type systems rule out more errors at the
cost of complicating the definition of what constitutes a legal
program.  (BTW, I agree that S-expressions are boring, but isn't it
interesting that the parenthetically-challenged have reinvented
S-expressions under the rubric of XML and think it is big deal?)

>Both you and Matthias seem to want to throw out
>static typing because it will never be complete.

I didn't notice any comment in Matthias's postings to this list that
suggested he thought static typing was useless, but I'll let him speak
for himself.

I have no antipathy toward static typing discplines, only toward false
statements made on their behalf.

-- Corky