- Inserted additional check for equality types in check_mode_clause that
avoids ill-typed code to be generated.
- Mode inference algorithm now outputs additional diagnostic messages.
types 'v binop = 'v => 'v => 'v
datatype ('a,'v) expr = Cex 'v
| Vex 'a
| Bex ('v binop) (('a,'v) expr) (('a,'v) expr)