Wordpress: Call to undefined function yaml_parse_file()

General Discussions
1 
$ curl http://localhost:8000

Among other things, appears:

Fatal error: Uncaught Error: Call to undefined function yaml_parse_file() in /var/www/html/wp-content/plugins/mytest/main.php

I suppose you need to install the php-imap extension (or something similar).
How you do it?

Here is my docker-compose.yml file:

version: '3.3'

services:
   db:
     image: mysql:5.7
     volumes:
       - dbdata:/var/lib/mysql
     restart: always
     environment:
       MYSQL_ROOT_PASSWORD: somewordpress
       MYSQL_DATABASE: wordpress
       MYSQL_USER: wordpress
       MYSQL_PASSWORD: wordpress

   wordpress:
        container_name: mytestplugin
        depends_on:
            - db
        image: wordpress:latest
        ports:
            - "8000:80"
        restart: always
        environment:
           WORDPRESS_DB_HOST: db:3306
           WORDPRESS_DB_USER: wordpress
           WORDPRESS_DB_PASSWORD: wordpress
        volumes:
            - .:/var/www/html/wp-content/plugins/mytest

volumes:
    dbdata:
2

I apologize.
I meant php-yaml extension (or something similar).