func_recursive.f90

! -*- Mode:F90; Coding:us-ascii-unix; fill-column:129 -*-
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.H.S.!!
!!
! @file      func_recursive.f90
! @author    Mitch Richling http://www.mitchr.me/
! @brief     Factorial computation via direct recursion with a function. @EOL
! @std       F95 
! @copyright 
!  @parblock
!  Copyright (c) 2024, Mitchell Jay Richling <http://www.mitchr.me/> All
!  rights reserved.
!
!  Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following
!  conditions are met:
!
!  1. Redistributions of source code must retain the above copyright notice, this list of conditions, and the following
!     disclaimer.
!
!  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions, and the following
!     disclaimer in the documentation and/or other materials provided with the distribution.
!
!  3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products
!     derived from this software without specific prior written permission.
!
!  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING,
!  BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
!  SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
!  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
!  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
!  TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
!  POSSIBILITY OF SUCH DAMAGE.
!  @endparblock
! @todo      @EOL@EOL
! @warning   @EOL@EOL
! @bug       @EOL@EOL
! @filedetails   
!
!  This program also demonstrates the RESULT keyword for function signatures
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.H.E.!!

!##################################################################################################################################
program func_recursive
  implicit none

  integer :: i

  do i=0,10
     print '(a,i2,a,i15)', 'ifact(', i, ')=', ifact(i)
  end do

contains

  recursive function ifact(n) result (ifactr)  ! RESULT required for direct recursion (silly, but true)
    integer, intent(in) :: n
    integer             :: ifactr
    if ( n <=1 ) then
       ifactr = 1
    else
       ifactr = n * ifact(n-1)
    end if
  end function ifact

end program func_recursive