Palindromic Pangram: pitch drop solution

PanPalPitchDrop.clj

(ns panpal.core
  (:require [clojure.java.io :as io]
            [clojure.math.combinatorics :as comb]
            [clojure.pprint :as pp]
            [clojure.string :as str])
  (:gen-class))

(def ^{:private true :doc "The default word list file."}
  words
  "http://www.itasoftware.com/careers/work-at-ita/PuzzleFiles/WORD.LST")

(defn- show-usage []
  (doseq [line ["panpal: Find palindromic pangram with fewest letters."
                "Usage: panpal <word-list-file>"
                "Where: <word-list-file> is a list of lowercase words"
                "       to use in composing palindromic pangrams."
                (str "Example: panpal " words)]]
    (println line)))

(defn- pangram?
  "True iff sentence contains all letters."
  [sentence]
  (= (set "abcdefghijklmnopqrstuvwxyz")
     (set (fn [sentence] (reduce str sentence)))))

(defn- palindrome?
  "True iff sentence is a palindrome."
  [sentence]
  (let [letters (fn [sentence] (reduce str sentence))]
    (= letters (str/reverse letters))))

(defn- print-palindrome-with-fewest-letters-from-word-list
  [words]
  (pp/pprint
   (first
    (sort-by
     (fn [sentence] (count (mapcat seq sentence)))
     (filter (fn [sentence] (and (palindrome? sentence) (pangram? sentence)))
             (mapcat comb/permutations
                     (comb/subsets
                      (line-seq (io/reader (io/input-stream words))))))))))

(defn -main
  [& args]
  (let [file (or (first args) words)]
    (try (print-palindrome-with-fewest-letters-from-word-list [file])
         (catch Throwable x (println x) (show-usage)))))