simple_function.f90

program simple_function

  implicit none

  integer :: val = -4
  logical :: res = .true.

  res = sign_test(val)

  print *,'Is the value positive ? : ', res
  
  contains

  logical function sign_test(input) result(output)
                                                  
    integer :: input

    if( input >= 0 ) then
      output = .true.
    else 
      output = .false.
    endif
  
  end function sign_test

end program simple_function