environment - an environment object. The default is nil, denoting the null lexical environment and the current global environment.

upgraded-typespec - a type specifier.

The typespec is a subtype of (and possibly type equivalent to) the upgraded-typespec.

If typespec is bit, the result is type equivalent to bit. If typespec is base-char, the result is type equivalent to base-char. If typespec is character, the result is type equivalent to character.

The purpose of upgraded-array-element-type is to reveal how an implementation does its upgrading.

The environment is used to expand any derived type specifiers that are mentioned in the typespec.

 (defun upgraded-array-element-type (type &optional environment)
   (array-element-type (make-array 0 :element-type type)))