module/slib/random.txi

   1
   2 @defun random n
   3
   4
   5 @defunx random n state
   6 Accepts a positive integer or real @var{n} and returns a number of the
   7 same type between zero (inclusive) and @var{n} (exclusive).  The values
   8 returned by @code{random} are uniformly distributed from 0 to @var{n}.
   9
  10 The optional argument @var{state} must be of the type returned by
  11 @code{(seed->random-state)} or @code{(make-random-state)}.  It defaults
  12 to the value of the variable @code{*random-state*}.  This object is used
  13 to maintain the state of the pseudo-random-number generator and is
  14 altered as a side effect of calls to @code{random}.
  15 @end defun
  16 @defvar *random-state*
  17 Holds a data structure that encodes the internal state of the
  18 random-number generator that @code{random} uses by default.  The nature
  19 of this data structure is implementation-dependent.  It may be printed
  20 out and successfully read back in, but may or may not function correctly
  21 as a random-number state object in another implementation.
  22 @end defvar
  23
  24
  25 @defun copy-random-state state
  26
  27 Returns a new copy of argument @var{state}.
  28
  29
  30 @defunx copy-random-state
  31 Returns a new copy of @code{*random-state*}.
  32 @end defun
  33
  34 @defun seed->random-state seed
  35
  36 Returns a new object of type suitable for use as the value of the
  37 variable @code{*random-state*} or as a second argument to @code{random}.
  38 The number or string @var{seed} is used to initialize the state.  If
  39 @code{seed->random-state} is called twice with arguments which are
  40 @code{equal?}, then the returned data structures will be @code{equal?}.
  41 Calling @code{seed->random-state} with unequal arguments will nearly
  42 always return unequal states.
  43 @end defun
  44
  45 @defun make-random-state
  46
  47
  48 @defunx make-random-state obj
  49 Returns a new object of type suitable for use as the value of the
  50 variable @code{*random-state*} or as a second argument to @code{random}.
  51 If the optional argument @var{obj} is given, it should be a printable
  52 Scheme object; the first 50 characters of its printed representation
  53 will be used as the seed.  Otherwise the value of @code{*random-state*}
  54 is used as the seed.
  55 @end defun