1. Florent Kaisser
  2. OpaGtkSourceView

Overview

Install:
 1.  Place opa.lang file in ~/.local/share/gtksourceview-3.0/language-specs/opa.lang 
 2.  Create a /usr/share/mime/packages/opa-mime.xml with this text:
     <?xml version="1.0" encoding="UTF-8"?>
     <mime-info xmlns='http://www.freedesktop.org/standards/shared-mime-info'>
       <mime-type type="text/x-opa">
         <comment>Opa programming language</comment>
         <glob pattern="*.opa"/>
       </mime-type>
     </mime-info>
 3.  Run update-mime-database /usr/share/mime