Whoa. That changes everything I thought I knew about ($). Come to think of it, one of the examples that does work it written main = print $ runST f where f is defined separtely. So that's consistent. I'll take a look at the references. Thanks!

Indeed. The short answer: use runST (long expression) rather than runST $ long expression

when it comes to higher-ranked functions such as runST. A longer answer: http://www.haskell.org/pipermail/haskell-cafe/2004-December/008062.html

...

let me know what i need to read to fix it myself MLF (see Daan Leijen, A. Loeh, `Qualified types for MLF', ICFP05)