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我正在用Clojure编写一个简单的桌面搜索引擎，作为了解更多关于该语言的一种方式。到目前为止，我的程序在文本处理阶段的表现非常糟糕。如何提高Clojure中的文本处理性能？
在文本处理我已经到：
- 清理不需要的字符;
- 将字符串转换为小写;
- 拆分文档以获取单词列表;
- 构建将每个单词与其文档中的出现相关联的映射。
下面是代码：
(ns txt-processing.core
(:require [clojure.java.io :as cjio])
(:require [clojure.string :as cjstr])
(:gen-class))
(defn all-files [path]
(let [entries (file-seq (cjio/file path))]
(filter (memfn isFile) entries)))
(def char-val
(let [value #(Character/getNumericValue %)]
{:a (value \a) :z (value \z)
:A (value \A) :Z (value \Z)
:0 (value \0) :9 (value \9)}))
(defn is-ascii-alpha-num [c]
(let [n (Character/getNumericValue c)]
(or (and (>= n (char-val :a)) (<= n (char-val :z)))
(and (>= n (char-val :A)) (<= n (char-val :Z)))
(and (>= n (char-val :0)) (<= n (char-val :9))))))
(defn is-valid [c]
(or (is-ascii-alpha-num c)
(Character/isSpaceChar c)
(.equals (str \newline) (str c))))
(defn lower-and-replace [c]
(if (.equals (str \newline) (str c)) \space (Character/toLowerCase c)))
(defn tokenize [content]
(let [filtered (filter is-valid content)
lowered (map lower-and-replace filtered)]
(cjstr/split (apply str lowered) #"\s+")))
(defn process-content [content]
(let [words (tokenize content)]
(loop [ws words i 0 hmap (hash-map)]
(if (empty? ws)
hmap
(recur (rest ws) (+ i 1) (update-in hmap [(first ws)] #(conj % i)))))))
(defn -main [& args]
(doseq [file (all-files (first args))]
(let [content (slurp file)
oc-list (process-content content)]
(println "File:" (.getPath file)
"| Words to be indexed:" (count oc-list)))))
当我有这个问题的another implementation在Haskell，我比较两者，你可以在下面的输出看到。
Clojure的版本：
$ lein uberjar
Compiling txt-processing.core
Created /home/luisgabriel/projects/txt-processing/clojure/target/txt-processing-0.1.0-SNAPSHOT.jar
Including txt-processing-0.1.0-SNAPSHOT.jar
Including clojure-1.5.1.jar
Created /home/luisgabriel/projects/txt-processing/clojure/target/txt-processing-0.1.0-SNAPSHOT-standalone.jar
$ time java -jar target/txt-processing-0.1.0-SNAPSHOT-standalone.jar ../data
File: ../data/The.Rat.Racket.by.David.Henry.Keller.txt | Words to be indexed: 2033
File: ../data/Beyond.Pandora.by.Robert.J.Martin.txt | Words to be indexed: 1028
File: ../data/Bat.Wing.by.Sax.Rohmer.txt | Words to be indexed: 7562
File: ../data/Operation.Outer.Space.by.Murray.Leinster.txt | Words to be indexed: 7754
File: ../data/The.Reign.of.Mary.Tudor.by.James.Anthony.Froude.txt | Words to be indexed: 15418
File: ../data/.directory | Words to be indexed: 3
File: ../data/Home.Life.in.Colonial.Days.by.Alice.Morse.Earle.txt | Words to be indexed: 12191
File: ../data/The.Dark.Door.by.Alan.Edward.Nourse.txt | Words to be indexed: 2378
File: ../data/Storm.Over.Warlock.by.Andre.Norton.txt | Words to be indexed: 7451
File: ../data/A.Brief.History.of.the.United.States.by.John.Bach.McMaster.txt | Words to be indexed: 11049
File: ../data/The.Jesuits.in.North.America.in.the.Seventeenth.Century.by.Francis.Parkman.txt | Words to be indexed: 14721
File: ../data/Queen.Victoria.by.Lytton.Strachey.txt | Words to be indexed: 10494
File: ../data/Crime.and.Punishment.by.Fyodor.Dostoyevsky.txt | Words to be indexed: 10642
real 2m2.164s
user 2m3.868s
sys 0m0.978s
哈斯克尔版本：
$ ghc -rtsopts --make txt-processing.hs
[1 of 1] Compiling Main (txt-processing.hs, txt-processing.o)
Linking txt-processing ...
$ time ./txt-processing ../data/ +RTS -K12m
File: ../data/The.Rat.Racket.by.David.Henry.Keller.txt | Words to be indexed: 2033
File: ../data/Beyond.Pandora.by.Robert.J.Martin.txt | Words to be indexed: 1028
File: ../data/Bat.Wing.by.Sax.Rohmer.txt | Words to be indexed: 7562
File: ../data/Operation.Outer.Space.by.Murray.Leinster.txt | Words to be indexed: 7754
File: ../data/The.Reign.of.Mary.Tudor.by.James.Anthony.Froude.txt | Words to be indexed: 15418
File: ../data/.directory | Words to be indexed: 3
File: ../data/Home.Life.in.Colonial.Days.by.Alice.Morse.Earle.txt | Words to be indexed: 12191
File: ../data/The.Dark.Door.by.Alan.Edward.Nourse.txt | Words to be indexed: 2378
File: ../data/Storm.Over.Warlock.by.Andre.Norton.txt | Words to be indexed: 7451
File: ../data/A.Brief.History.of.the.United.States.by.John.Bach.McMaster.txt | Words to be indexed: 11049
File: ../data/The.Jesuits.in.North.America.in.the.Seventeenth.Century.by.Francis.Parkman.txt | Words to be indexed: 14721
File: ../data/Queen.Victoria.by.Lytton.Strachey.txt | Words to be indexed: 10494
File: ../data/Crime.and.Punishment.by.Fyodor.Dostoyevsky.txt | Words to be indexed: 10642
real 0m9.086s
user 0m8.591s
sys 0m0.463s
我认为（串 - >懒惰序列）在Clojure的实现转换查杀性能。我该如何改进它？
P.S：这些测试中使用的所有代码和数据可以下载here。
什么jar是JVM的启动时间吗？ Haskell有类似的开销吗？ – georgek 2013-04-27 23:40:36
我机器中的JVM启动时间大约为1秒。我认为Haskell由于运行时系统（RTS）有一些开销，但我应该比JVM低得多。 – luisgabriel 2013-04-28 00:41:41
s /我应该/它应该/ – luisgabriel 2013-04-28 01:18:43