parsing question

[Matthew Fluet]

I've been bitten by this a couple of times (usually when I start a self
compile, and come back to find that it died during parsing), so I was
wondering if it is a bug in MLton or SML/NJ.  Essentially, what is the
grammar for structure paths: the following program is parsed by SML/NJ,
but MLton finds illegal tokens on lines 2, 3, and 4:

val _ = Math.sin 5.0
val _ = Math. sin 5.0
val _ = Math .sin 5.0
val _ = Math . sin 5.0