Aleks,
On Mon, 2013-04-15 at 19:15 +0100, Aleks Kissinger wrote:
This is more of a standard ML question, but I figure folks here will know. I've always found the situations in which poly/ML allows polymorphic values (versus forcing a monotype) a bit puzzling. [...]
Perhaps others will answer in more detail, but until then, you could try searching for "SML value restriction".
Best, Tjark