Re: Using "internal" macros of a CL implementation

Ken Tilton <kentilton@xxxxxxxxx> writes:

Victor Kryukov wrote:
Hello group,

I've the following question: I want to define macro case-string, which
behaves exactly like case, only using string-equal instead of eql.

I've looked up definition of case in SBCL[*], and realized that my
task is as simple as

(defmacro case-string (keyform &body cases)
(case-body 'case keyform cases t 'string-equal nil nil nil))

COND.

Let me be more precise here. I do understand how to use COND to
achieve what I need. I just want more useful macro, so that

(let ((keyform "test"))
(case-string keyform
("test1" 'test1)
(("test2" "test3") 'test2-or-3)
(("test" "test4") 'test-or-4)))

would evaluate to TEST-OR-4. Of course, you can do that simply by
using COND, as Ken suggested:

(cond
((string= keyform "test1") 'test1)
((member keyform '("test2" "test3") :test #'string=) 'test2-or-3)
((member keyform '("test" "test4") :test #'string=) 'test-or-4))

and is seems not that hard to write case-string macro which translates
first snippet to the second. I've just noticed that similar
functionality already existed in SBCL core - e.g. case is really
similar, it's only uses 'eql instead of string=, and is defined with
help of internal macro case-body; my question was how one can possibly
access such macros (even in non-portable way) to avoid duplicating
existing functionality.

Victor.
.

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