eql => eq?

[DILL at CMU-20C]

Proposal: rename the function "eq" in common lisp to be something like
"si:internal-eq-predicate", and the rename "eql" to be "eq".  This would
have several advantages.

 * Simplification by reducing the number of equality tests.

 * Simplification by reducing the number of different versions of
   various predicates that depend on the type of equality test you
   want.

 * Greater machine independence of lisp programs (whether eq and equal
   are the same function for various datatypes is heavily
   implementation-dependent, while eql is defined to be relatively
   machine-independent; furthermore, functions like memq in the current
   common lisp proposal make it easier to use eq comparisons than eql).

Possible disadvantages:

 * Do people LIKE having, say, numbers with identical values not be eq?
   If so, they won't like this.

 * Efficiency problems.

I don't believe the first complaint.  If there are no destructive
operations defined for an object, eq and equal ought to do the same
thing.

The second complaint should not be significant in interpreted code,
since overhead of doing a type-dispatch will probably be insignificant
in comparison with, say, finding the right subr and calling it.

In compiled code, taking the time to declare variable types should allow
the compiler to open-code "eq" into address comparisons, if appropriate,
even in the absence of a hairy compiler.  A hairy compiler could do even
better.

Finally, in the case where someone wants efficiency at the price of
tastefulness and machine-independence, the less convenient
implementation-dependent eq could be used.
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