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.

Sign-up for Cognitect dev-tools license

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

Accept the Cognitect dev-tools license to receive an email containing a link to download the latest version of Datomic local and a personal access token for access to the Cognitect Maven repository which contains the REBL library.

Either install the REBL jar file using Maven directly, or add the Cognitect Maven server and Cognitect Provider configuration to access REBL as any other library dependency.

Install REBL jar via Maven locally

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

In a terminal, run the install file (requires maven installed and available via the command line)


Add Congnitect Maven Server

The Cognitect REBL package is only available via the Cognitect Maven Repository via a personal token. The token is provided when signing up to Cognitect dev-tools license.

Create or edit the ~/.m2/settings.xml file and add the following configuration, replacing the <value> with your own personal token (which should not be shared).


Add Cognitect as Provider

In the Maven provider section of ~/.clojure/deps.edn add the Cognitect Maven repository details

:mvn/repos {"cognitect-dev-tools"
             {:url ""}}

Create an alias for Cognitect REBL

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

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

JavaFX library dependencies need to be explicitly added from Java 9 onward

{: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"}
                ;; deps for file datafication (REBL 0.9.149 or later)
                org.clojure/data.csv        {:mvn/version "1.0.0"}
                org.clojure/data.json       {:mvn/version "1.0.0"}
                org.yaml/snakeyaml          {:mvn/version "1.27"}}
 :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:inspect/rebl

If rlwrap is installed, then use:

clj -M:inspect/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 :middleware/nrebl alias along with the supporting :lib/cider-nrepl aliases are included in practicalli/clojure-deps-edn configuration

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

  {:extra-deps {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 "0.8.2"}
                cider/cider-nrepl             {:mvn/version "0.25.3"}
                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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