doctest software package provides test interactive Haskell examples; executable, 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 doctest
doctest is installed in your system.
Make ensure the doctest package were installed using the commands given below,
$ sudo dpkg-query -l | grep doctest *
You will get with doctest package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Development |
| Package | doctest |
| Version | 0.11.0-1+b1 [armel, armhf], 0. |
| Description | test interactive Haskell examples; executable |
| Sub Section | devel |