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Code Evaluation#

Calva tries to make it easy to evaluate code, supporting interactive development. The fastest path to learning about it is to use the Fire up the Getting Started REPL command, which you can learn more about in the Getting Started section.

NB: The below assumes you have read about Finding Calva Commands and Shortcuts.

Interrupting/stopping running evaluations#

Sometimes you evaluate things that take a very long time to complete, or might not even ever complete (infinite loops, lazy sequences, things like that). Calva has a command for interrupting running evaluations. You find it in the VS Code command palette, as well as in the REPL status bar item menu, when the REPL is connected.

Evaluation in a File Editor#

Calva has many commands for evaluating forms, including the current form and the current top-level form.

Some of the commands also let you choose what should happen with the results:

  1. Inline. This will display the results (or some of it, if it is long) inline in the editor.
  2. This also creates a hover pane including the full results and a button which will copy the results to the clipboard.
  3. There is also a command for copying the last result to the clipboard.
  4. The full results are always available in the output window.
    • There is a command for showing the output window, allowing for a workflow where you either generally have it closed, or have it as one of the tabs in the same editor group as the files you are working with.
  5. To comments. This will add the results as line comments below the current line.
  6. Replace the evaluated code. This will do what it says, the evaluated code will be replaced with its results.

Wait, Current Form? Top-level Form?#

These are important concepts in Calva in order for you to create your most effective workflow. This video explains it a bit:

Current Form#

Default shortcut for evaluating the current form: ctrl+enter.

The current form either means the current selection, or otherwise is based on the cursor position. Play some with the command Calva: Select current form, ctrl+alt+c s, to figure out what Calva thinks is the current form for some different situations. Try it inside a symbol, adjacent to a symbol (both sides) and adjacent to an opening or closing bracket (again, both sides). Generally the current form is determined like so:

  1. If text is selected, then that text
  2. If the cursor is ”in” a symbol, then that symbol 
    foob|ar ; foobar
  3. If the cursor is adjacent to a form (a symbol or a list of some kind), then that form 
    (foo bar |(baz)) ; (baz)
  4. If the cursor is between to forms, then the left side form 
    (foo bar | (baz)) ; bar
  5. If the cursor is before the first form of a line, then that form 
    (foo
| bar (baz)) ; bar

Current Top-level Form#

Default shortcut for evaluating the current top level form: alt+enter.

The current top-level form means top-level in a structural sense. It is not the topmost form in the file. Typically in a Clojure file you will find def and defn (and defwhatever) forms at the top level, which also is one major intended use for evaluating top level form: to define and redefine variables. However, Calva does not check the contents of the form in order to determine it as a top-level forms: all forms not enclosed in any other form are top level forms.

An ”exception” is introduced by the comment form. It will create a new top level context, so that any forms immediately inside a (comment ...) form will be considered top-level by Calva. This is to support a workflow with what is often referred to the Rich Comments.

At the top level the selection of which form is the current top level form follows the same rules as those for the current form.

Evaluate Enclosing Form#

The default keyboard shortcut for evaluating the current enclosing form (the list the cursor is in) is ctrl+shift+enter.

(let [foo :bar]
  (when false (str| foo))) ; => ":bar"

Evaluate to Cursor#

There are several commands for evaluating a piece of code, closing brackets. It's good, especially in threads, but can also come in handy in other situations, for instance when you want to evaluate something that depends on bindings, such as in a let form.

Evaluate From Start of List to Cursor, Closing Brackets#

This command evaluates the text from the start of the current enclosing list to where the cursor is, and it adds the missing closing bracket for you. Convenient for checking intermediate results in thread or doto, or similar pipelines. The cursor is right behind :d in this form:

  (->> [1 1 2 3 5 8 13 21]
       (partition 2)
       (zipmap [:a :b :c :d])
       :d| ; => (13 21)
       (apply -)
       (Math/abs))

The default shortcut for this command is ctrl+alt+enter.

Evaluate Selection, Closing Brackets#

This is the most versatile of the ”evaluation, closing brackets” commands. It will do what it says. 😄 It's extra handy in combination with the command Paredit: Select Backward Up Sexp/Form (shift+ctrl+up). Consider this contrieved form (buggy code, because it was supposed to result in 42, not -42):

(defn fortytwo-from-thirty
  []
  (let [thirty 30]
    (-> thirty
        inc            ;1
        (send-off)
        (+ 1 2 3)
        (->>
         (+ 2 2)       ;2
         (+))
        list
        (->>
         (into [1])
         (reduce + 1))
        (- 1)          ;3
        (* -1))))

At ;1, you can do backward up sexp (shift+ctrl+up) twice to select up to the (let ..), then issue Evaluate Selection, Closing Brackets. It has the same default keybinding as the command for evaluating the current list up to the cursor: ctrl+alt+enter.

At ;2 you need select backwards up three times.

;3 is included because it is close to the bug. (Which was introduced when the thread-last, ->> was added to make this example.) Please practice the Evaluate Selection, Closing Brackets command to fix the bug.

Evaluate From Start of Top Level Form to Cursor, Closing Brackets#

This command has a default shortcut keybinding of shift+alt+enter. It will create a form from the start of the current top level form, up to the cursor, close all brackets, and this will then be evaluated. Good for examining code blocks up to a certain point. Often comes in handy in Rich comments ((comment ...)).

Take this example and paste it in a file loaded into the REPL, then place the cursor in front of each line comment and try the command.

(comment
 (do
   (def colt-express
     {:name "Colt Express"
      :categories ["Family"
                   "Strategy"]
      :play-time 40
      :ratings {:pez 5.0
                :kat 5.0
                :wiw 5.0   ; 1, then eval `colt-express`
                :vig 3.0
                :rex 5.0
                :lun 4.0}})

   (defn average [coll]
     (/ (apply + coll) (count coll)))

   (let [foo-express (-> colt-express
                         (assoc :name "Foo Express")
                         (assoc-in [:ratings :lyr] 5.0)
                         (update-in [:ratings :vig] inc))]
     (->> foo-express   ; 2
          :ratings      ; 3
          vals          ; 4
          average       ; 5
          ))))

Evaluate From Start of File to Cursor, Closing Brackets#

Yup, that command also exists. 😄

Copying the inline results#

There is a command called Copy last evaluation results, ctrl+alt+c ctrl+c.

This works regardless if you have evaluated in a file editor or in a REPL window.

Evaluating in a REPL window#

Since the REPL Window is mostly just a regular file, things work pretty similar at the REPL prompt. You use alt+enter to evaluate. Selecting the current form (default key binding ctrl+w on Mac and shift+alt+right on Windows and Linux) after evaluating will select the result.