Columnar Output

The io.aviso.columns namespace is what’s used by the exceptions namespace to format the exceptions, properties, and stack traces.

The format-columns function is provided with a number of column definitions, each of which describes the width and justification of a column. Some column definitions are just a string to be written for that column, such as a column separator. format-columns returns a function that accepts the column values and writes the formatted column data to out.

write-rows takes the function provided by format-columns, plus a set of functions to extract column values, plus a seq of rows. In most cases, the rows are maps, and the extraction functions are keywords (isn’t Clojure magical that way?).

Here’s an example, based on code in the exception namespace:

(defn ^:private write-stack-trace
  (let [elements (->> exception expand-stack-trace (map preformat-stack-frame))
        formatter (c/format-columns [:right (c/max-value-length elements :formatted-name)]
                                    "  " (:source *fonts*)
                                    [:right (c/max-value-length elements :file)]
                                    [:right (->> elements (map :line) (map str) c/max-length)]
                                    (:reset *fonts*))]
    (c/write-rows formatter
                   #(if (:line %) ": ")