Cognitect REBL data browser

Cognitect REBL is a interactive tool for capturing the results of evaluating expressions and visualizing that data for human consumption. REBL was initially created to support development with the Datomic database and is useful viewing and navigating data structures, especially nested data structures and large data sets.

Clojure REBL data browser

Install REBL

REBL is part of the Cognitect dev-tools project that also includes Datomic dev-local (local running instance of Datomic).

The Cognitect install script requires maven to be installed locally

Visit the Cognitect dev-tools web page and provide an email address. An email will be sent containing a link to download the latest version of Cognitect dev-tools (0.9.34 at time of writing).

Click the link in the email to download the .zip file and extract the .zip file.

In a terminal, run the install file (assuming maven is installed)


Create an alias for Cognitect REBL

A :cognitect-rebl alias is included in practicalli/clojure-deps-edn configuration

Add an alias called :cognitect-rebl to ~/.clojure/deps.edn or a deps.edn file in the root of a specific project

If using Java11 for your projects then JavaFX library dependencies need to be explicitly added (JavaFX was separated from the Java distribution from Java 9 onwards).

  {:extra-deps {com.cognitect/rebl          {:mvn/version "0.9.241"}
                org.clojure/core.async      {:mvn/version "1.3.610"}
                org.openjfx/javafx-fxml     {:mvn/version "11.0.1"}
                org.openjfx/javafx-controls {:mvn/version "11.0.1"}
                org.openjfx/javafx-swing    {:mvn/version "11.0.1"}
                org.openjfx/javafx-base     {:mvn/version "11.0.1"}
                org.openjfx/javafx-web      {:mvn/version "11.0.1"}}
   :main-opts  ["-m" "cognitect.rebl"]}

Java8 contains JavaFX, so only the REBL library dependencies is required.

  {:extra-deps {com.cognitect/rebl {:mvn/version "0.9.241"}}
   :main-opts  ["-m" "cognitect.rebl"]}

Running REBL with a project

Run the project using the Clojure CLI tools

clojure -M:cognitect-rebl

If rlwrap is installed, then use:

clojure -M:cognitect-rebl

Configure REBL with CIDER for Spacemacs / Emacs

nrebl.middleware is an nREPL middleware library that will spy on an nREPL connection and sent the results of every evaluation to Cognitect REBL.

Cognitect REBL with CIDER in Spacemacs

This library is described as very alpha but works in basic tests run by Practicalli.

An :nrebl alias along with the supporting :nrepl :cider-nrepl aliases are included in practicalli/clojure-deps-edn configuration

Add an alias called :nrebl to ~/.clojure/deps.edn or a deps.edn file in the root of a specific project

  {:extra-deps {nrepl/nrepl                   {:mvn/version "0.7.0"}
                cider/cider-nrepl             {:mvn/version "0.25.0"}
                refactor-nrepl/refactor-nrepl {:mvn/version "2.5.0"}
                rickmoynihan/nrebl.middleware {:mvn/version "0.3.1"}}
   :main-opts  ["-e" "((requiring-resolve,'cognitect.rebl/ui))"
                "-m" "nrepl.cmdline"
                "--middleware" "[nrebl.middleware/wrap-nrebl,cider.nrepl/cider-middleware]"]}

Supporting aliases for nrebl.middleware

  {:extra-deps {nrepl/nrepl {:mvn/version "0.7.0"}}}

  {:extra-deps {cider/cider-nrepl             {:mvn/version "0.25.0"}
                refactor-nrepl/refactor-nrepl {:mvn/version "2.5.0"}}}

Run REBL for nREPL based editors

CIDER and Calva use the nREPL protocol to connect to the REBL REPL and have all the evaluated code in those editors automatically display the results in the REBL UI.

In a terminal, run REBL listening to nREPL using the command

clojure -M:lib/cider-nrepl:inspect/rebl:middleware/nrebl

Then cider-connect-clj in Spacemacs / Emacs and CIDER will connect to the nREPL port and results of evaluated code are sent to REBL UI.

To start a REBL REPL from cider-jack-in-clj add a .dir-locals.el file to the root of a Clojure project. The .dir-locals.el configuration adds the nREBL aliases set via cider-clojure-cli-global-options and all other automatically injected configuration is disabled (to prevent those dependencies over-riding the nREBL aliases).

((clojure-mode . ((cider-preferred-build-tool . clojure-cli)
                  (cider-clojure-cli-global-options . "-M:lib/cider-nrepl:inspect/rebl:middleware/nrebl")
                  (cider-jack-in-dependencies . nil)
                  (cider-jack-in-nrepl-middlewares . nil)
                  (cider-jack-in-lein-plugins . nil)
                  (cider-clojure-cli-parameters . ""))))

revert-buffer to load .dir-locals.el

revert-buffer will force Emacs to load in the .dir-locals.el configuration if it was added to a project with files already opened.

See the excellent guide on using VSCode Calva with REBL


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