gnat-5 software package provides GNU Ada compiler, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gnat-5
gnat-5 is installed in your system.
Make ensure the gnat-5 package were installed using the commands given below,
$ sudo dpkg-query -l | grep gnat-5 *
You will get with gnat-5 package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Development |
| Package | gnat-5 |
| Version | 5.4.1-3 |
| Description | GNU Ada compiler |
| Sub Section | devel |