'for' can be handy when unpacking compound lines:
(ns foobar
(:require [clojure.java.io :as io]))
(defn parse-acl [acl-file]
(with-open [r (io/reader acl-file)]
(apply
merge-with into
(for [[status users path] (map #(.split % "\\|") (line-seq r))
:when (= "avail" status)
user (.split users ",")]
{user [path]}))))
Justin
On Mar 3, 9:15 pm, Stefan Rohlfing <[email protected]> wrote:
> Dear Clojure Group,
>
> I am currently reading the online book Pro Git <http://progit.org/book/>. In
> chapter 7.4 <http://progit.org/book/ch7-4.html> (section “Enforcing a
> User-Based ACL System”) there is a task of reading in an access control list
> (ACL) file, such as the following
>
> # avail/unavail | users | path
> avail|nickh,pjhyett,defunkt,tpw
> avail|usinclair,cdickens,ebronte|doc
> avail|schacon|lib
> avail|schacon|tests
>
> and printing out a map of the form { "user1" [path 1, path 2], "user2"
> [path2, path3] ...}.
>
> The author of the book provides a solution in Ruby, which I find relatively
> easy to follow, despite not having written any Ruby code before:
>
> def get_acl_access_data(acl_file)
> # read in ACL data
> acl_file = File.read(acl_file).split("\n").reject { |line| line == '' }
> access = {}
> acl_file.each do |line|
> avail, users, path = line.split('|')
> next unless avail == 'avail'
> users.split(',').each do |user|
> access[user] ||= []
> access[user] << path
> end
> end
> access
> end
>
> I then tried the same in Clojure, but found my solution to be much less
> readable compared to the Ruby code:
>
> (use '[clojure.string :only (split)])
>
> (defn get-acl-access-data [file]
> (let [acl (split (slurp file) #"\n")]
> (apply merge-with #(into %1 %2)
> (map (fn [[avail users path]]
> (let [users (split users #",")]
> (reduce (fn [acc user]
> (when (= avail "avail")
> (assoc acc user [path])))
> {} users)))
> (map #(split % #"\|") acl)))))
>
> ;; Output:
> ;; {"schacon" ["lib" "tests"],
> ;; "usinclair" ["doc"],
> ;; "cdickens" ["doc"],
> ;; "ebronte" ["doc"],
> ;; "tpw" [nil],
> ;; "defunkt" [nil],
> ;; "pjhyett" [nil],
> ;; "nickh" [nil]}
>
> Maybe it is just because I am an ambitious beginner at best, but I am afraid
> I won’t be able to figure out immediately what this code is doing in a few
> weeks.
>
> However, there probably is a better way of translating the Ruby version into
> Clojure. With "better" I mean easier to follow. My main goal is on clarity,
> as I often struggle organizing my code in a way I would consider readable.
>
> I therefore would be glad for any ideas of improvement. Any suggestions are
> highly welcome!
>
> Best regards,
>
> Stefan
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