About

Walkr (walk-reduce) is a Clojure library built to help you easily walk-reduce clojure data structures.

Usage

Here's a simple example.

(ns user
  (:require [walkr.core :as w]
            [clojure.string :as str]))

(w/prewalk-reduce
  (fn [acc item]
    (if (string? item)
      [(conj acc (str/lower-case item)) (str/upper-case item)]
      [acc item]))
  #{}
  [{:foo {:bar {:value #{"cOlD"}}
                      :other "hOt"}}
   {:foo {:bar {:value "ColDer"}
          :other "hoTteR"}}])
;;; =>
;;; [#{"cold" "hot" "colder" "hotter"}
;;;  [{:foo {:bar {:value #{"COLD"}}
;;;          :other "HOT"}}
;;;   {:foo {:bar {:value "COLDER"}
;;;          :other "HOTTER"}}]]

You can also walk multiple collections in tandem. The first collection drives the traversal shape; each additional trailing collection is walked alongside it (paired by key for maps, by value/membership for sets, by index for vectors/lists/seqs), and its corresponding value is passed as extra, read-only context to your callback. Only the first collection is transformed and rebuilt.

(w/postwalk-reduce
  (fn [acc item & secondary-items]
    (if (number? item)
      [(conj acc (into [item] secondary-items)) item]
      [acc item]))
  []
  {:a 1 :b 2}
  {:a 10 :b 20})
;;; =>
;;; [[[1 10] [2 20]] {:a 1 :b 2}]

Note: for sets, pairing is by value/membership rather than position — a set element is its own key, so the corresponding secondary value is that same element if it's also present in the secondary set, or nil otherwise.

See the existing tests for more examples.

Building

walkr is built, tested, and deployed using Clojure Tools Deps.

GNU Make is used to simplify invocation of some commands.

Availability

gateless/walkr releases for this project are on Clojars. Simply add the following to your project:

Communication

• For any other questions or issues about walkr free to browse or open a Github Issue.

Contributing

See CONTRIBUTING.md

YourKit

YourKit supports open source projects with innovative and intelligent tools for monitoring and profiling Java and .NET applications. YourKit is the creator of YourKit Java Profiler, YourKit .NET Profiler, and YourKit YouMonitor.

LICENSE

Copyright 2025 Gateless

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.