[plt-scheme] Why do folks implement *dynamically* typed languages?

I find this analogy quite amusing, since every time I use PowerPoint I have to manually turn off all 
the autocorrect options because it invariably corrects things in ways I don't want.  I find myself 
saying "just do what I want!" over and over again.  Apparently other M$ products do the same; I had 
a friend write me an email about improv comedy where all the "improv"s were changed to "improve" -- 
after all, everyone knows that "improv" isn't a word, right?

BTW one aspect of this discussion that Matthias alluded to but didn't describe in detail is 
languages with dependent type systems e.g. Epigram.  In those languages, the type system is 
extremely powerful but also undecidable, so the programmer takes on the proof obligations 
him/herself.  My impression is that advanced statically-typed languages are moving in this 
direction, which may make the boundary between such languages and Scheme very small indeed.

Mike

Mark Engelberg wrote:
> I like Matthias' comparison of static type checking in programming to
> a spell checker in writing.
> 
> Spell checkers are useful, but would you use a spell checker if the
> cost of doing so was that your word processor would not allow you to
> use any words in your document that were not in the spell checker's
> dictionary?  It might be worth it to you if you're a really bad
> speller, if you're working on a pretty standard document with no
> specialized vocabulary, or if you simply tend to be unimaginative in
> your word choice.  Of course, the spell checker can't guarantee your
> document is perfect -- if you make a typo replacing one word with
> another legal word, the checker probably won't pick up on that.  So
> really, you need to proofread your document anyway.  Good spellers
> will make few mistakes, and will catch almost all of the mistakes upon
> proofreading their own paper.  Those people would gladly ditch a
> constraining spellchecker, finding it of limited value, and prefer the
> freedom of expression that comes from choosing their own words.
> 
> --Mark