pass function as argument to subroutine using interface doesn't work in Plato Fortran 90

Question

I created a fortran 90 program that I used on a linux machine and compiled using gfortran. It worked fine on the linux machine with gfortran but provides the error

error 327 - In the INTERFACE to SECANTMETHOD (from MODULE SECMETH), the ninth dummy argument (F) was of type REAL(KIND=2) FUNCTION, whereas the actual argument is of type REAL(KIND=2)

when using the Plato compiler (FTN95). Does anyone know how I would need to change my code to work in Plato? I tried to read up on this error and there was some mention of pointers but from what I tried that did not work. I have figured out some workarounds but they make it so that the subroutine can no longer accept any function as an argument - which is pretty much useless. Any help would be greatly appreciated. My code is below.

!--! A module to define a real number precision.
module types
  integer, parameter :: dp=selected_real_kind(15)
end module types

module secFuncs
  contains

  function colebrookWhite(T)
    use types

    real(dp) :: colebrookWhite
    real(dp), intent(in) :: T

    colebrookwhite=25-T**2

    return
  end function colebrookWhite
end module secFuncs

module secMeth
  contains

  subroutine secantMethod(xolder,xold,xnew,epsi1,epsi2,maxit,exitFlag,numit,f)
    use types
    use secFuncs
    implicit none

    interface
      function f(T)
        use types
        real(dp) :: f
        real(dp), intent(in) :: T
      end function f
    end interface

    real(dp), intent(in) :: epsi1, epsi2
    real(dp), intent(inout) :: xolder, xold
    real(dp), intent(out) :: xnew
    integer, intent(in) :: maxit
    integer, intent(out) :: numit, exitFlag
    real(dp) :: fxold, fxolder, fxnew
    integer :: i

    fxolder = f(xolder)
    fxold = f(xold)

    i = 0

    do
      i = i + 1

      xnew = xold - fxold*(xold-xolder)/(fxold-fxolder)

      fxnew = f(xnew)

      if (i == maxit) then
        exitFlag = 1
        numit = i
        return
      else if (abs(fxnew) < epsi1) then
        exitFlag = 2
        numit = i
        return
      else if (abs(xnew - xold) < epsi2) then
        exitFlag = 3
        numit = i
        return
      end if

      xolder = xold
      xold = xnew
      fxolder = fxold
      fxold = fxnew
    end do
  end subroutine secantMethod

end module secMeth

program secantRoots
  use types
  use secMeth
  use secFuncs
  implicit none

  real(dp) :: x1, x2, xfinal, epsi1, epsi2
  integer :: ioerror, maxit, numit, exitFlag

  do
    write(*,'(A)',advance="no")"Please enter two initial root estimates, 2epsi's, and maxit: "
    read(*,*,iostat=ioerror) x1, x2, epsi1, epsi2, maxit

    if (ioerror /= 0) then
      write(*,*)"Invalid input."
    else
      exit
    end if
  end do

  call secantMethod(x1,x2,xfinal,epsi1,epsi2,maxit,exitFlag,numit,colebrookWhite)

  if (exitFlag == 1) then
    write(*,*)"The maximum number of iterations was reached."
  else if (exitFlag == 2) then
    write(*,'(a,f5.3,a,i3,a)')"The root is ", xfinal, ", which was reached in ", numit, " iterations."
  else if (exitFlag == 3) then
    write(*,'(a,i3,a)')"There is slow or no progress at ", numit, " iterations."
  end if

end program secantRoots

Answer 1

Current gfortran detects the error in the call to the secantMethod procedure, where you have parentheses, but no argument list, following the colebrookWhite function name.

If you want to pass a function as an argument (as opposed to the result of evaluating a function), which is what you want to do here, you do not follow the function name with a parenthesis pair.

call secantMethod(x1,x2,xfinal,epsi1,epsi2,maxit,exitFlag,numit,colebrookWhite )
!                                                                             ^

Answer 2

I ended up just switching from Plato to Geany IDE (I actually like Geany WAY better now that I've used it for a couple hours), setting up gfortran with Geany, and the code works with that setup. I'm guessing the reason I'm getting the error with Plato is that its compiler is actually a fortran95 compiler while gfortran is a fortran90 compiler. It took a while to get everything working but once I downloaded mingw-w64 for gfortran and set the path user (not system) environment variable to the correct location everything works great. I would still be interested in seeing if there is a way to get the code working with the FTN95 compiler, but in the end I'm still sticking with gfortran and Geany.