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

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