('[':s) -> False -- []
('$':c:s) -> not (isAlpha c) -- Don't treat $d as an operator
(':':c:s) -> not (isAlpha c) -- Don't treat :T as an operator
+ ('_':s) -> False -- Not an operator
(c:s) -> not (isAlpha c) -- Starts with non-alpha
other -> False
-- We use (showSDoc (ppr v)), rather than isSymOcc (getOccName v) simply so