* Binding *APPROXIMATE-NUMERIC-UNIONS* does that. It must be bound
only by callers of TYPE-UNION that know what they want -- in general
(OR (INTEGER 1 2) (INTEGER 3 4)) => (INTEGER 1 4)
is wrong, as (NOT (INTEGER 1 4)) doesn't include 3. But in special cases
like deriving the return type of a function it can be done.
* Rename MAKE-CANONICAL-UNION-TYPE MAKE-DERIVED-UNION-TYPE, and bind *A-N-U*
there if we start accumulating an overly large union of numeric types.
Definition of "overly large" can be adjusted via
* Fixes lp#309448 and the recent compiler performance regression due
to new CONCATENATE deftransform as reported on sbcl-devel.