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わかる!Java to Clojure
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Shunsuke Tadokoro
October 05, 2017
Technology
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1.8k
わかる!Java to Clojure
2017.10.4「教養としてのClojure」の発表資料です
Shunsuke Tadokoro
October 05, 2017
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Transcript
Θ͔Δʂ+BWBUP$MPKVSF ڧཁڭཆͱͯ͠ͷ$MPKVSF EDMK !UPEPLS ָ͘͠
୭ͩ ాॴॣ༎!UPEPLS ීஈ4DBMBΤϯδχΞ ϓϥΠϕʔτͰ$MPKVSF$MPKVSF4DSJQUΛͪΐͪ͜ΐ͜৮Δॳ৺ऀ
None
͓͢͠Δ͜ͱ w 8IZ-JTQ 8IZ$MPKVSF w جຊతͳจ๏ʹ͍ͭͯ w +BWBͷΞϨΛ$MPKVSFͰॻ͍ͯΈΑ͏
8IZ-JTQ w େֶͰ৮͍ͬͯͨͷͰ w ࣄͷͨΊ w ʮܭࢉػϓϩάϥϜͷߏͱղऍʯΛಡΉͨΊ w &NBDTϢʔβʔͩͬͨͷͰ w
+BWB4DSJQU$ͷൽΛ͔Ϳͬͨ-JTQͩͱฉ͍ͯ w ϧϯό͕-JTQͰಈ͍͍ͯΔͱฉ͍ͯ w FUD
None
ϙʔϧɾάϨΞϜ 7JBXFCۀऀ :$PNCJOBUPSઃऀ
-JTQͰྑ͍ϓϩάϥϜ͕ॻ͚ΔͳΒɺ͏͖ͳΜͩɻ ͦ͏Ͱͳ͍ͳΒ͍͍ͬͨԿͷʹཱͭ ϙʔϧɾάϨΞϜ 7JBXFCۀऀ :$PNCJOBUPSઃऀ
ී௨ͷౕΒͷ্Λߦ͚ɻ -JTQͰྑ͍ϓϩάϥϜ͕ॻ͚ΔͳΒɺ͏͖ͳΜͩɻ ͦ͏Ͱͳ͍ͳΒ͍͍ͬͨԿͷʹཱͭ ϙʔϧɾάϨΞϜ 7JBXFCۀऀ :$PNCJOBUPSઃऀ
ී௨ͷౕΒͷ্Λߦ͚ɻ -JTQͰྑ͍ϓϩάϥϜ͕ॻ͚ΔͳΒɺ͏͖ͳΜͩɻ ͦ͏Ͱͳ͍ͳΒ͍͍ͬͨԿͷʹཱͭ ϙʔϧɾάϨΞϜ 7JBXFCۀऀ :$PNCJOBUPSઃऀ :BIPPʹച٫
ී௨ͷౕΒͷ্Λߦ͚ɻ -JTQͰྑ͍ϓϩάϥϜ͕ॻ͚ΔͳΒɺ͏͖ͳΜͩɻ ͦ͏Ͱͳ͍ͳΒ͍͍ͬͨԿͷʹཱͭ ϙʔϧɾάϨΞϜ 7JBXFCۀऀ :$PNCJOBUPSઃऀ Θͨ͠ ී௨ͷϓϩάϥϚ -JTQͰΣϒαʔϏεΛͭ͘Δͱ :BIPPʹԯԁͰങͬͯΒ͑Δʂʂʂ
:BIPPʹച٫
ͳͥ$PNNPO-JTQ4DIFNFͰͳ͘ $MPKVSFʁ
8IZ$MPKVSF w ಡΈ͢͞ w ׅހͷ͕গͳ͍ w ׅހͷछྨ͕ଟ͍ w #FUUFS+BWBͰ͋Δ͜ͱ w
ϦονɾώοΩʔ
8IZ$MPKVSF w ಡΈ͢͞ w ׅހͷ͕গͳ͍ w ׅހͷछྨ͕ଟ͍ w #FUUFS+BWBͰ͋Δ͜ͱ w
ϦονɾώοΩʔ
ಡΈ͢͞ $MPKVSF-JTQͷ౷ΛࣺͯɺಡΈ͢͞ΛͱͬͨʢΒ͍͠ʣ ͦͷͨΊɺ$PNNPO-JTQ4DIFNFʹൺͯ ɾׅހ͕গͳ͍ ɾׅހͷछྨ͕ଟ͍
ಡΈ͢͞ ͨͱ͑ؔͷҾ $PNNPO-JTQ 4DIFNF $MPKVSF (defun square (x) (* x
x)) (define (square x) (* x x)) (defn square [x] (* x x))
ಡΈ͢͞ ͨͱ͑BTTPDJBUJWFͳσʔλߏʢ+BWBͰ͍͏.BQʣ (defparameter greet '(("ja" . "͜Μʹͪ") ("en" . "hello")
("fr" . "bonjour")) (define greet '(("ja" "͜Μʹͪ") ("en" "hello") ("fr" "bonjour")) $PNNPO-JTQ 4DIFNF (def greet {"ja" "͜Μʹͪ" "en" "hello" "fr" "bonjour"}) $MPKVSF
8IZ$MPKVSF w ಡΈ͢͞ w ׅހͷ͕গͳ͍ w ׅހͷछྨ͕ଟ͍ w #FUUFS+BWBͰ͋Δ͜ͱ w
ϦονɾώοΩʔ
8IZ$MPKVSF w ಡΈ͢͞ w ׅހͷ͕গͳ͍ w ׅހͷछྨ͕ଟ͍ w #FUUFS+BWBͰ͋Δ͜ͱ w
ϦονɾώοΩʔ
#FUUFS+BWBͰ͋Δ͜ͱ (.concat "hello" " world") ; -> "hello world" ;;
"hello".concat(" world"); (.getName String) ; -> "java.lang.String" ; String.getName (.. user getAddress getCity) ; -> "Shibuya" ; user.getAddress().getCity(); (.-x (new java.awt.Point 2 3)) ;; 2 ;; -> new java.awt.Point(2, 3).x Math/PI ;; 3.141592653589793 ;; Math.PI +BWBͷ"1*͕ͦͷ··ݺͼग़ͤΔ☕️ ˠ+BWBͰͰ͖Δ͜ͱͰ͖Δʂͱ͍͏҆৺ײ
8IZ$MPKVSF w ಡΈ͢͞ w ׅހͷ͕গͳ͍ w ׅހͷछྨ͕ଟ͍ w #FUUFS+BWBͰ͋Δ͜ͱ w
ϦονɾώοΩʔ
8IZ$MPKVSF w ಡΈ͢͞ w ׅހͷ͕গͳ͍ w ׅހͷछྨ͕ଟ͍ w #FUUFS+BWBͰ͋Δ͜ͱ w
ͳʹΑΓָ͍͠ʂ
ͳʹΑΓָ͍͠ʂ w ߴ֊ؔԆධՁͳͲͷؔܕϓϩάϥϛϯάελΠϧ w ঢ়ଶʹ͍ͭͯͷߟ͑ํɺ*EFOUJUZ 4UBUF 7BMVFͷ w γϯϓϧ͞ʹ͍ͭͯ ͍Ζ͍Ζܹత
IUUQCPYPGQBQFSTIBUFOBCMPHDPNFOUSZTJNQMF@NBEF@FBTZ
ͭ·Γ$MPKVSF ͱ͖͍ͬͭ͢ʂ ֶͼָ͕͍͋ͬͯ͠ʂ
+BWBUP$MPKVSFͯ͠ΈΑ͏ w )FMMPXPSME w ࢛ଇԋࢉ w มએݴ w ؔએݴ w
ແ໊ؔ
खݩͰࢼ͢ͳΒ5SZ$MPKVSF͕͓͢͢Ί w 5SZ$MPKVSF IUUQXXXUSZDMKDPN
·ͣγϯλοΫεʹ׳ΕΑ͏ʂ
-JTQͷγϯλοΫε ׅހͷ࢝·Γ͔ΒऴΘΓ·Ͱ͕୯Ґ (ԿΒ͔ͷॲཧ ॲཧͷରͳͲ…)
͏׳Ε·ͨ͠Ͷ
)FMMPXPSME System.out.println("Hello world"); +BWB $MPKVSF
)FMMPXPSME System.out.println("Hello world"); +BWB (println "Hello world") $MPKVSF
࢛ଇԋࢉ 12 + 40 10 - 1 2 * 3
5 / 2 +BWB $MPKVSF
࢛ଇԋࢉ 12 + 40 10 - 1 2 * 3
5 / 2 +BWB (+ 12 40) (- 10 1) (* 2 3) (/ 5 2) $MPKVSF
࢛ଇԋࢉ 12 + 40 10 - 1 2 * 3
5 / 2 +BWB (+ 12 40) (- 10 1) (* 2 3) (/ 5 2) ; -> 5/2 Λѻ͏Ratioܕ $MPKVSF
˞จࣈྻͷ݁߹TUS จࣈྻͷ݁߹ Ͱͳ͘TUSΛ͏ (+ "hoge" "fuga") ClassCastException java.lang.String cannot be
cast to java.lang.Number clojure.lang.Numbers.add (Numbers.java:128) (str "hoge" "fuga") hogefuga
มએݴ int x = 10; +BWB $MPKVSF
มએݴ int x = 10; +BWB (def x 10) $MPKVSF
มએݴ MFUʹΑΔϩʔΧϧมఆٛʢϩʔΧϧଋറʣΛݟ͔͚Δ΄͏͕ଟ͍ (let [x 10] (+ x 3)) ; xletͷׅހ͚ͩͰࢀরͰ͖Δ
$MPKVSF
ؔએݴ public int f(int x) { return x + 1;
} +BWB $MPKVSF
ؔએݴ public int f(int x) { return x + 1;
} +BWB (defn f [x] (+ x 1)) $MPKVSF
ແ໊ؔ x -> x * 2 +BWB $MPKVSF
ແ໊ؔ x -> x * 2 +BWB (fn [x] (*
x 2)) $MPKVSF
ແ໊ؔ x -> x * 2 +BWB (fn [x] (*
x 2)) #(* % 2) ; ↑ͷ؆ܿͳه๏ $MPKVSF
ແ໊ؔΛͬͯΈΔ Arrays.asList(1, 2, 3).stream() .map(x -> x * 2) .collect(Collectors.toList());
// List(2, 4, 6) +BWB $MPKVSF
ແ໊ؔΛͬͯΈΔ Arrays.asList(1, 2, 3).stream() .map(x -> x * 2) .collect(Collectors.toList());
// List(2, 4, 6) +BWB (map (fn [x] (* x 2)) '(1 2 3)) $MPKVSF
ແ໊ؔΛͬͯΈΔ Arrays.asList(1, 2, 3).stream() .map(x -> x * 2) .collect(Collectors.toList());
// List(2, 4, 6) +BWB (map (fn [x] (* x 2)) '(1 2 3)) (map #(* % 2) '(1 2 3)) $MPKVSF
ͬͱ+BWBUP$MPKVSFͯ͠ΈΑ͏ w γʔέϯεͷจࣈྻ݁߹ w จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ w *OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ
γʔέϯεͷจࣈྻ݁߹
γʔέϯεͷจࣈྻ݁߹ String[] words = { "a", "b", "c" }; StringBuilder
sb = new StringBuilder(); for(String word : words) { sb.append(word); } System.out.println(sb.toString()); // "abc" // Java8 System.out.println(String.join("", words)); +BWBͷ߹
γʔέϯεͷจࣈྻ݁߹ (def words '("a" "b" "c")) (clojure.string/join "" words) ;
͘͠ (apply str words) DMPKVSFͷ߹
γʔέϯεͷจࣈྻ݁߹ (def words '("a" "b" "c")) (clojure.string/join "" words) ;
͘͠ (apply str words) DMPKVSFͷ߹
w ՄมҾΛड͚औΔؔʹγʔέϯεΛ͍ͨ͠ͱ͖ʹ͏ w +BWB4DSJQUͷBQQMZͱҰॹ BQQMZ (str ["a" "b" "c"]) ;
-> ["a" "b" "c"] (apply str ["a" "b" "c"]) ; -> abc ; (str "a" "b" "c") ͱಉ͡
γʔέϯεͷจࣈྻ݁߹ (def words '("a" "b" "c")) (clojure.string/join "" words) ;
͘͠ (apply str words) DMPKVSFͷ߹
จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ
จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ public static boolean isBlank(final CharSequence cs) { int strLen;
if (cs == null || (strLen = cs.length()) == 0) { return true; } for (int i = 0; i < strLen; i++) { if (!Character.isWhitespace(cs.charAt(i))) { return false; } } return true; } isBlank("hello!"); // false isBlank(null); // true isBlank(""); // true isBlank("\r\n\t") // true +BWBͷ߹
จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ (defn blank? [s] (every? #(Character/isWhitespace %) s)) (blank? "helllo!")
; false (blank? nil) ; true (blank? "") ; true (blank? "\n\r\t") ; true DMPKVSFͷ߹
จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ (defn blank? [s] (every? #(Character/isWhitespace %) s)) (blank? "helllo!")
; false (blank? nil) ; true (blank? "") ; true (blank? "\n\r\t") ; true DMPKVSFͷ߹
FWFSZ w ίϨΫγϣϯͷશͯͷཁૉʹରͯ͠ ड़ޠؔʢCPPMFBOΛฦؔ͢ʣΛద༻ w શͯUSVFͳΒUSVF (every? even? '(2 4
6)) ; true (every? even? '(1 2 3)) ; false
จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ (defn blank? [s] (every? #(Character/isWhitespace %) s)) (blank? "helllo!")
; false (blank? nil) ; true (blank? "") ; true (blank? "\n\r\t") ; true DMPKVSFͷ߹
*OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ
*OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ try(BufferedReader reader = new BufferedReader( new InputStreamReader( new FileInputStream("./test.txt"))))
{ StringBuilder sb = new StringBuilder(); String line; while((line = reader.readLine()) != null) { sb.append(line); } System.out.println(sb.toString()); } +BWBͷ߹
*OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ (require [clojure.java.io :as io]) (with-open [bis (io/input-stream "./test.txt")] (println
(slurp bis))) $MPKVSFͷ߹
*OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ (require [clojure.java.io :as io]) (with-open [bis (io/input-stream "./test.txt")] (println
(slurp bis))) $MPKVSFͷ߹
DMPKVSFKBWBJPJOQVUTUSFBN w ҾͰड͚औͬͨ'JMF 63* 63- 4PDLFU CZUFྻ 4USJOHʢͰදݱ͞ΕͨύεʣΛ*OQVU4USFBNʹม w มޙͷ*OQVU4USFBNͷσϑΥϧτ࣮
KBWBJP#VGGFSFE*OQVU4USFBN (require '[clojure.java.io :as io]) (io/input-stream "http://example.com")
XJUIPQFO w +BWBͰ͍͏USZXJUISFTPVSDFߏจɺ 4DBMBͰ͍͏-PBO1BUUFSOΛ࣮ݱ͢Δͷ w XJUIPQFOͰPQFOͨ͠ϦιʔεউखʹDMPTF͞ΕΔ (with-open [in (io/input-stream "./test.txt")]
(do-something in)) ;; already closed!
TMVSQ w 3FBEFS #VGGFSFE3FBEFS *OQVU4USFBN 'JMF 63* 63- 4PDLFU
CZUFྻ DIBSྻΛड͚औΓɺ จࣈྻʹͯ͠ฦ͢ w ରʹͳΔॻ͖ग़͠ͷͨΊͷؔTQJU (spit "./test.txt" "hello I/O!") (println (slurp "./test.txt")) ;; -> hello I/O!
*OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ (require [clojure.java.io :as io]) (with-open [bis (io/input-stream "./test.txt")] (println
(slurp bis))) $MPKVSFͷ߹
*OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ (require [clojure.java.io :as io]) (with-open [bis (io/input-stream "./test.txt")] (println
(slurp bis))) $MPKVSFͷ߹ ;; όοϑΝϦϯάͤͣʹϑΝΠϧ͔ΒಡΉ͚ͩͳΒˣͰOK (println (slurp "./test.txt"))
ࠓ+BWBUP$MPKVSFͨ͠ͷ w )FMMPXPSME w ࢛ଇԋࢉ w มએݴ w ؔએݴ w
ແ໊ؔ w γʔέϯεͷจࣈྻ݁߹ w จࣈྻ͕ۭPSۭനจࣈ͔Ͳ͏͔ͷఆ w *OQVU4USFBN͔ΒจࣈྻΛͯ͢ಡΉ
None