Unix sort in Clojure

Question

I am implementing Unix sort in Clojure. This is my first program, and I would like some feedback regarding any non-idiomatic, harmful code and any other best practices I can include in future versions. I tried my best to follow the coding standards, but went with camelCase instead of hyphen-case for variable and function names.

Main class: sort.core

(ns sort.core
 (:gen-class)
 (:use clojure.contrib.core)
 (:use clojure.tools.cli)
 (:require [sort.lib :as lib]))
(defn -main [& args]
 (let [[options args banner] (cli args 
 ["-h" "--help" "Show help" :default false :flag true]
 ["-i" "--input" "The input file" :default nil]
 ["-d" "--delim" "The delimitter" :default ","]
 ["-f" "--field" "The column to parse(1 indexed)" :parse-fn #(Integer. %)])
 {:keys [delim field input]} options]
 (lib/help options args banner)
 (when (= (lib/fileKind input) "file")
 (lib/printOutVector delim
 (lib/sortVector field
 (lib/splitFile input delim ))))
 (System/exit 0)))

Library: sort.lib

(ns sort.lib
 (:require [clojure.string :as str])
 (:import java.io.File))
(defn splitFile 
 "splits a file into a 2d array" 
 [s delim] 
 (pmap #(str/split % (re-pattern delim)) 
 (str/split(slurp s) #"\n")))
(defn printOutVector
 "prints out the 2dVector formatted by the delim arg"
 [delim coll] 
 (println 
 (apply str 
 (interpose "\n" (map #(apply str (interpose delim %)) coll)))))
(defn sortVector 
 "sorts a 2d vector by the given index"
 [index coll]
 (sort-by #(nth % index) coll))
(defn help 
 "custom help message for sort.core"
 [opts args banner] 
 (when (:help opts)
 (println (str "input: " (:input opts)))
 (println (str "field: " (:field opts)))
 (println (str "delim: " (:delim opts)))
 (println banner)
 (System/exit 0)))
(defn fileKind [filename]
 (let [f (File. filename)]
 (cond
 (.isFile f) "file"
 (.isDirectory f) "directory"
 (.exists f) "other" 
 :else "(non-existent)" )))

Answer 1

You should use namespace-qualified keywords instead of strings in the fileKind function:

(defn fileKind [filename]
 (let [f (File. filename)]
 (cond
 (.isFile f) ::file
 (.isDirectory f) ::directory
 (.exists f) ::other 
 :else ::non-existent)))

... which would require the following change in the -main function:

(= (lib/fileKind input) :lib/file)

• wespiserA: looks like you're gonna win the bounty, have anything else to say?
• rreillo: Not really, I don't think I'd do it very differently.
• rreillo: I guess your usage of pmap is a bit clumsy and could lead to decreased performance for large files due to the extra overhead. You might want to take a look at this: fatvat.co.uk/2009/05/jvisualvm-and-clojure.html