idiomatic clojure prefix replacement

Question

I have a map representing information about a subversion commit.

Example contents:

(def commit 
  {:repository "/var/group1/project1"
   :revision-number "1234"
   :author "toolkit"
   etc..}

I would like to change the repository based on a prefix match, so that:

/var/group1 maps to http://foo/group1
/var/group2 maps to http://bar/group2

I have created 2 functions like:

(defn replace-fn [prefix replacement]
  (fn [str]
    (if (.startsWith str prefix)
      (.replaceFirst str prefix replacement)
      str)))

(def replace-group1 (replace-fn "/var/group1" "http://foo/group1"))
(def replace-group2 (replace-fn "/var/group2" "http://bar/group2"))

And now I have to apply them:

(defn fix-repository [{:keys [repository] :as commit}]
  (assoc commit :repository
    (replace-group1
      (replace-group2 repository))))

But this means I have to add an extra wrapper in my fix-repository for each new replacement.

I would like to simply:

• Given a commit map
• Extract the :repository value
• Loop through a list of replacement prefixes
• If any prefix matches, replace :repository value with the new string
• Otherwise, leave the :repository value alone.

I can't seem to build the right loop, reduce, or other solution to this.

Answer 1

How about something like this?

(defn replace-any-prefix [replacements-list string]
  (or (first
        (filter identity
          (map (fn [[p r]]
                 (when (.startsWith string p)
                    (.replaceFirst string p r)))
               replacements-list)))
      string)))

(update-in commit
           [:repository]
           (partial replace-any-prefix
                    [["/var/group1" "http://foo/group1"]
                     ["/var/group2" "http:/foo/group2"]]))

Documentation for update-in: http://clojuredocs.org/clojure_core/clojure.core/update-in