/usr/share/acl2-6.3/books/tools/safe-case.lisp is in acl2-books-source 6.3-5.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | ; Safe-Case Macro
; Copyright (C) 2008-2010 Centaur Technology
;
; Contact:
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; http://www.centtech.com/
;
; This program is free software; you can redistribute it and/or modify it under
; the terms of the GNU General Public License as published by the Free Software
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; version. This program is distributed in the hope that it will be useful but
; WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
; FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
; more details. You should have received a copy of the GNU General Public
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; Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA.
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; Original author: Jared Davis <jared@centtech.com>
(in-package "ACL2")
(defmacro safe-case (&rest l)
":Doc-Section Case
Error-checking alternative to `case'.~/
~c[;; (include-book \"tools/safe-case\" :dir :system)] ~/
~c[Safe-case] is a drop-in replacement for ~il[case], and is logically identical
to ~c[case]. The only difference is during execution. When ~c[case] is used and
none of the cases match, the answer is ~c[nil]:
~bv[]
ACL2 !> (case 3
(1 'one)
(2 'two))
NIL
~ev[]
But when ~c[safe-case] is used and none of the cases match, the result is an
error:
~bv[]
ACL2 !> (safe-case (+ 0 3)
(1 'one)
(2 'two))
HARD ACL2 ERROR in SAFE-CASE: No case matched:
(SAFE-CASE (+ 0 3) (1 'ONE) (2 'TWO)). Test was 3.
~ev[]"
(declare (xargs :guard (and (consp l)
(legal-case-clausesp (cdr l)))))
(let* ((clauses (cdr l))
(tests (strip-cars clauses)))
(if (or (member t tests)
(member 'otherwise tests))
`(case ,@l)
`(case ,@l
(otherwise
(er hard? 'safe-case "No case matched: ~x0. Test was ~x1.~%"
'(safe-case ,@l) ,(car l)))))))
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