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R4RS 4.2.1 (case <key> <clause1> <clause2> ...) ==> object
Syntax: <Key> may be any expression. Each <clause> should have the
form
((<datum1> ...) <expression1> <expression2> ...),
where each <datum> is an external representation of some object.
All the <datum>s must be distinct. The last <clause> may be an "else
clause," which has the form
(else <expression1> <expression2> ...).
Semantics: A CASE expression is evaluated as follows. <Key> is
evaluated and its result is compared against each <datum>. If the
result of evaluating <key> is equivalent (in the sense of EQV?; see
section see section 6.2 Equivalence predicates) to a <datum>, then
the expressions in the corresponding <clause> are evaluated from
left to right and the result of the last expression in the <clause>
is returned as the result of the CASE expression. If the result of
evaluating <key> is different from every <datum>, then if there is
an ELSE clause its expressions are evaluated and the result of the
last is the result of the case expression; otherwise the result of
the CASE expression is unspecified.
(case (* 2 3)
((2 3 5 7) 'prime)
((1 4 6 8 9) 'composite)) ==> composite
(case (car '(c d))
((a) 'a)
((b) 'b)) ==> unspecific
(case (car '(c d))
((a e i o u) 'vowel)
((w y) 'semivowel)
(else 'consonant)) ==> consonant
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