! qsort_reals.f90 --
!
!     Example belonging to "Modern Fortran in Practice" by Arjen Markus
!
!     This work is licensed under the Creative Commons Attribution 3.0 Unported License.
!     To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/
!     or send a letter to:
!     Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.
!
!     Compact implementation of the QuickSort algorithm
!
!     Note:
!     Because the function uses Fortran 90 features, its interface should be made
!     explicit when using it in an actual program. This is easiest via a module.
!
module qsort_functions
    implicit none
contains
recursive function qsort_reals( data ) result( sorted )
    real, dimension(:), intent(in) :: data
    real, dimension(1:size(data))  :: sorted

    if ( size(data) > 1 ) then
        sorted = &
            (/ qsort_reals( pack( data(2:), data(2:) > data(1) ) ), &
               data(1),                                             &
               qsort_reals( pack( data(2:), data(2:) <= data(1) ) ) /)
    else
        sorted = data
    endif
end function qsort_reals
end module qsort_functions