runST, :i :t and :n

[Graeme Moss]

(Usual apologies if this has been reported before, I've had a quick
scan of the archive and the known bugs but couldn't find anything.)

I know that the type of `runST' is not within the realms of standard
Haskell but I've noticed some odd behaviour from Hugs (971118):

Prelude> :i runST
runST :: <unknown type>   -- primitive

Prelude> :n runST
runST
(1 names listed)
Prelude> :t runST 
ERROR: Syntax error in expression (unexpected end of input)
Prelude> :l ST