A by-name parameter type of the form
=> T, or the type of a method with no parameter list.
Compute hashcode relative to enclosing binders
Equality used for hash-consing; uses
eq on all recursive invocations,
except where a BindingType is involved. The latter demand a deep isomorphism check.
this isomorphic to
that, assuming pairs of matching binders
It is assumed that
The resultType of a LambdaType, or ExprType, the type itself for others
hash of this type the same for all possible sequences of enclosing binders?