[Sorry for the belated reply... still catching
up from whatever the local cold/flu crud was...]

Vassil Nikolov  <vnikolov+usenet@pobox.com> wrote:
+---------------
| rpw3@rpw3.org (Rob Warnock) said:
| |     (defun my-eql (x y)
| |       (cond
| | 	((eq x y)
| | 	 t)
| | 	((and (characterp x) (characterp y))
| | 	 (char= x y))
| | 	((and (complexp x) (complexp y))
| | 	 (and (my-eql (realpart x) (realpart y))
| | 	      (my-eql (imagpart x) (imagpart y))))
| | 	((and (numberp x)
| | 	      (numberp y)
| | 	      (subtypep (type-of x) (type-of y))
| | 	      (subtypep (type-of y) (type-of x)))
| | 	 (= x y))
| | 	(t
| | 	 nil))
| 
|   You can use = for complex numbers as well.
+---------------

Uh... Actually, no you can't!!  :-(

    > (= #c(4 5) #c(4.0 5.0))

    T
    > (eql #c(4 5) #c(4.0 5.0))

    NIL
    > 

Look at the bottom of the CLHS "Function EQL" page which
specifically discusses this case, and which is why I put
the test for COMPLEX before the test for NUMBER:

    Two complex numbers are considered to be eql if their
    real parts are eql and their imaginary parts are eql.

Compare with CLHS "Function =", which says:

    Two complexes are considered equal by = if their real
    and imaginary parts are equal according to =.

But EQL & "=" treat fixed & float equality differently:

    > (= 4 4.0)

    T
    > (eql 4 4.0)

    NIL
    > 

+---------------
| A bigger worry is the use of TYPE-OF, though---somehow,
| it lacks that proverbial warm, fuzzy feeling...
+---------------

I didn't like it either, but I couldn't think of any other way to
exactly match the semantics of the CLHS "Function EQL", which says:

    2. If x and y are both numbers of the same type and the same value.


-Rob

-----
Rob Warnock			<rpw3@rpw3.org>
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