regress/roff/de/factorial.in

   1 .\" $OpenBSD: factorial.in,v 1.2 2017/07/04 14:53:27 schwarze Exp $
   2 .Dd $Mdocdate: July 4 2017 $
   3 .Dt FACTORIAL 1
   4 .Os
   5 .Sh NAME
   6 .Nm factorial
   7 .Nd factorial sequence
   8 .Sh DESCRIPTION
   9 .\" recursively calculate a single factorial
  10 .de rfac
  11 .  ie \\$1>1 \{\
  12 .    No \\$1 *
  13 .    nr i \\$1-1
  14 .    rfac \\ni
  15 .    nr acc \\n[acc]*\\$1
  16 .  \}
  17 .  el .nr acc 1
  18 ..
  19 .\" recursively print a sequence of factorials
  20 .de fac
  21 .  No \\$1! =
  22 .  rfac \\$1
  23 .  if \\$1>1 1 =
  24 .  No \\n[acc]
  25 .  if \\$1 \{\
  26 .    br
  27 .    nr i \\$1-1
  28 .    fac \\ni
  29 .  \}
  30 ..
  31 .\" main program
  32 .fac 9