The example on the page shows the guideline in two forms: the first is a more natural-language style syntax, and the second is something close to TypeScript, a web programming language.
We can make the Expression Language work in either style, very easily. The questions are:
what kind of professional will create these kinds of guidelines, and also rules inside archetypes?
what style of syntax is better to use?
It is early days for guideline and rule authoring, but it will certainly come. So it would be helpful to get some ideas from the community on this. You could reply here, or comment on the wiki page linked above.
As a clinician / informatician I prefer the first style, but for most people not familiar with scripting or coding both will look too abstract to pick up and run with off the bat.
In Scotland we are planning to use GDL but we are very early days in the process. Our intention is to skill up a number of guideline / decision support developers (probably from the jointly clinical/technical skilled people, but not developers as such) to be able to author and maintain these apps for us, and also to encourage independent developers and companies to do the same. I guess that the people authoring these things will be both from developer and clinical communities, and will need to work together regardless to actually create meaningful and useful decision support.