Channel Directions in Fortran

In Fortran, we don’t have built-in channels like in some other languages. However, we can simulate similar behavior using derived types and procedures. This example demonstrates how to create a simple message passing system in Fortran.

module channel_module
  implicit none
  private

  type, public :: channel
    character(len=100) :: message
  end type channel

  public :: ping, pong

contains

  subroutine ping(pings, msg)
    type(channel), intent(inout) :: pings
    character(len=*), intent(in) :: msg
    pings%message = msg
  end subroutine ping

  subroutine pong(pings, pongs)
    type(channel), intent(in) :: pings
    type(channel), intent(out) :: pongs
    pongs%message = pings%message
  end subroutine pong

end module channel_module

program main
  use channel_module
  implicit none

  type(channel) :: pings, pongs

  call ping(pings, "passed message")
  call pong(pings, pongs)
  print *, trim(pongs%message)

end program main

In this Fortran version:

1. We define a channel type in a module to simulate a channel-like structure.

2. The ping subroutine takes a channel and a message as input. It sets the message in the channel.

3. The pong subroutine takes two channels: one for input (pings) and one for output (pongs). It transfers the message from the input channel to the output channel.

4. In the main program, we create two channel variables, pings and pongs.

5. We call ping to send a message through the pings channel.

6. We then call pong to transfer the message from pings to pongs.

7. Finally, we print the message received in the pongs channel.

To run this Fortran program:

$ gfortran channel_directions.f90 -o channel_directions
$ ./channel_directions
passed message

This example demonstrates how to implement a simple message passing system in Fortran, which is conceptually similar to channel directions in other languages. While Fortran doesn’t have built-in channel primitives, we can create similar behavior using derived types and procedures.