Learn Datalog

An interactive web app for learning Datomic Datalog.

The app serves a series of exercises. Each exercise includes an editable Datalog query that runs against a Datomic database populated with Pokemon data.

Stack

• http-kit - HTTP server
• Compojure - Routing
• Hiccup - HTML rendering from Clojure data structures
• Datomic - Database
• Datastar - Frontend reactivity
• Code Highlighter - Editable code blocks with syntax highlighting

Development

Start the server:

clojure -X:run

Run tests:

clojure -X:test

Build an uberjar:

clojure -T:build uber

Adding a chapter

Chapters are EDN files in resources/chapters/.

1. Create resources/chapters/<slug>.edn. The slug becomes the URL (/<slug>):

   {:nav-title "My chapter"
    :content
    [:div
     [:h1 "My chapter"]
     [:p "Some text."]
     [:ui/runnable "pokemon" [:find ?name :where [?e :pokemon/name ?name]]]
     [:ui/try-tip [:p "Change the query above."]]]}

2. Add the slug to resources/chapters/chapters.edn. Its position sets the order in the nav. Files not listed there are not published.

:content is plain Hiccup. Four extra tags call functions:

Tag	Renders
[:ui/runnable dataset query & inputs]	An editable query with Run and Reset buttons. Any inputs after the query are passed to its :in clause in order, after $. A vector of rules is the input for %. (as-of "Generation V"), (since "Generation V") and (history) are views of the database, see the Time travel chapter.
[:ui/code query]	A read-only code block from data, pretty-printed.
[:ui/code lang string]	A read-only code block from a string, shown as written.
[:ui/try-tip hiccup]	A highlighted "TRY" box.
[:ui/value dataset query]	The result of a scalar query, like [:find (count ?e) . :where [?e :pokemon/name _]], shown as text. Use it for any number in the text that comes from the data, so the text can't go stale when the data changes.

In development the files are re-read on every request, so refreshing the browser shows your edits. clojure -X:test checks that every chapter loads and renders, and that every runnable query is allowed and executes.

Deployment

fly deploy