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Improve extensibility of expt' and integer-expt'

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* libguile/numbers.c (scm_integer_expt): No longer require that the
  first argument be a number, in order to improve extensibility.  This
  allows us to efficiently raise arbitrary objects to an integer power
  as long as we can multiply those objects.  For example, this allows us
  to efficiently exponentiate matrices if we define only multiplication
  methods for matrices.  Note also that scm_expt calls this procedure
  whenever the exponent is an integer, regardless of the type of the
  first argument.  Also rearrange the order in which we test special
  cases.

* test-suite/tests/numbers.test (expt, integer-expt): Comment out tests
  that required `(expt #t 0)' and `(integer-expt #t 0)' to throw
  exceptions.  Add tests for (expt #t 2) and `(integer-expt #t 2)
  instead.

* NEWS: Add NEWS entry
This commit is contained in:
Mark H Weaver 2011-01-30 10:51:36 -05:00 • committed by Andy Wingo
parent 05a5e5d6d0
commit bfe1f03aac
3 changed files with 42 additions and 14 deletions
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19
test-suite/tests/numbers.test
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@ -3110,8 +3110,21 @@
(with-test-prefix "expt"
(pass-if (documented? expt))
(pass-if-exception "non-numeric base" exception:wrong-type-arg
(expt #t 0))
;;
;; expt no longer requires its first argument to be a scheme number,
;; for the sake of extensibility, and expt calls integer-expt for
;; integer powers. To raise to a positive power, all that is required
;; is that it can be multiplied using `*'. For negative powers we
;; must also be able to find the reciprocal. If we try to raise #t to
;; any power other than 0 or 1 it may throw an exception, depending on
;; whether * has been defined for #t. However, when raising to the 0
;; or 1 power, the first argument is not manipulated at all.
;;
;; (pass-if-exception "non-numeric base" exception:wrong-type-arg
;; (expt #t 0))
;;
(pass-if (eqv? 1 (expt 0 0)))
(pass-if (eqv? 1 (expt 0.0 0)))
(pass-if (eqv? 1.0 (expt 0 0.0)))
@ -3277,8 +3290,6 @@
(with-test-prefix "integer-expt"
(pass-if (documented? integer-expt))
(pass-if-exception "non-numeric base" exception:wrong-type-arg
(integer-expt #t 0))
(pass-if-exception "2^+inf" exception:wrong-type-arg
(integer-expt 2 +inf.0))
(pass-if-exception "2^-inf" exception:wrong-type-arg