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Node, Promises and Functional Programming
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Yuta Okamoto
April 25, 2013
Programming
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1.7k
Node, Promises and Functional Programming
東京Node学園 8時限目 ”Nodeとプロミスと、時々、関数型” by @okapies
http://connpass.com/event/2125/
Yuta Okamoto
April 25, 2013
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Transcript
Nodeͱϓϩϛεͱ ࣌ʑɺؔܕ @okapies
୭ʁ • Ԭຊ ༤ଠ (@okapies) • Java/Scala ϓϩάϥϚ • ؔܕϓϩάϥϛϯάमߦத…
• ٕज़จॻͷ༁Λ͍͔ͭͬͯ͘·͢ • Effective Scala (http://twitter.github.io/effectivescala/ index-ja.html) • “Scala Conference in Japan 2013” ༁νʔϜ
ܦҢ
Java VMͷ ੩తܕ͖ݴޠ ΦϒδΣΫτࢦʴؔܕ
ඇಉظRPCϥΠϒϥϦ”Finagle” Scala ͷ Node.jsʂ Tumblr, 4sqར༻ from http://twitter.github.io/finagle/ Twitter͕։ൃ
Future/Promise͕େ׆༂
ͦΜͳ͋Δ…
None
“Callbacks are imperative, promises are functional” from http://blog.jcoglan.com/2013/03/30/callbacks-are-imperative-promises-are-functional-nodes-biggest-missed-opportunity/
ஶऀ: James Coglan͞Μ • ΠΪϦεͷ Ruby/JavaScript ϓϩάϥϚ • Haskellؔܕϓϩάϥϛϯάʹৄ͍͠ •
FayeɺHeistɺJS.Classͷ࡞ऀ
هࣄͷཁ • ”Node.jsίʔϧόοΫͰͳ͘ϓϩϛεΛ࠾ ༻͢Δ͖ͩͬͨ”ͱओுɻ • ϓϩϛεϞσϧ͕༏Ε͍ͯΔཧ༝Λɺ๛ͳ ۩ମྫΛݩʹղઆɻ • ͱ͍ͯ
͕Μͬͯಡഁ
㱺 ἤΒΕΔ
͏͓͒͒…ʢඞࢮʣ
͏ɺΰʔϧ͍͍ͯ͠ΑͶ…ʁ from https://gist.github.com/okapies/5354929
Oh...
ຊ͓ট͖͍͖ͨͩ ͋Γ͕ͱ͏͍͟͝·͢ m( _ _ )m
None
ඇಉظϓϩάϥϛϯά
ඇಉظॲཧΛॻ࣌͘ʹ ԿΛߟ͑Δʁ A. λεΫಉ࢜ͷґଘؔΛߟ͑Δɻ B. ඞཁͳૢ࡞ͷॱংΛߟ͑Δɻ C.BΛ࣮ݱ͢Δ੍ޚϑϩʔΛॻ͘ɻ
ίʔϧόοΫ vs. ϓϩϛε ※Ҏ߱ͷίʔυྫجຊతʹ ”Promises are functional...” ΑΓҾ༻ɻ
// fs.readFile(filename, callback) fs.readFile('file1.txt', // ͠Β͕࣌ؒ͘ܦͭͱ... function(error, buffer) { //
݁Ռ͕ඈͼग़ͯ͠ݱΕΔ } }; ίʔϧόοΫ
ίʔϧόοΫͷྑ͘ͳ͍ͱ͜Ζ • ॲཧΛϞδϡʔϧԽͨ͠ΓΈཱͯͨΓ ͢Δͷ͕͍͠ɻ • ஞ࣍ॲཧ͔ฒྻॲཧ͔Λ໌ࣔతʹ੍ޚ͢ Δඞཁ͕͋Δɻ
”ωετࠈ (Pyramid of Doom)”ຊ࣭Ͱͳ͍ step1(function (value1) { step2(value1, function(value2) {
step3(value2, function(value3) { step4(value3, function(value4) { // ... }); }); }); });
ྫ
ྫ: ෳͷϑΝΠϧΛฒྻతʹ fs.stat ͯ͠ mtime ΛऔΓग़͢ɻ file1 file2 file3 stat
mtime stat stat mtime mtime ฒྻॲཧ શͯͷ݁Ռ͕ ἧͬͨΒ࣍
var async = require('async'), fs = require('fs'); var paths =
['file1.txt', 'file2.txt', 'file3.txt']; async.map(paths, fs.stat, function(error, stats) { // stats Λ͏ }); file1 file2 file3 stat mtime stat stat mtime mtime OK!
ผͷॲཧΛ ͚͍ͨ͠…
file1 ͷ size Λ͏ॲཧΛՃ͢Δɻ file1 file2 file3 stat mtime stat
stat mtime mtime size
var paths = ['file1.txt', 'file2.txt', 'file3.txt']; async.map(paths, fs.stat, function(error, stats)
{ // stats Λ͏ }); fs.stat(paths[0], function(error, stat) { // stat.size Λ͏ }); file1 file2 file3 stat mtime stat stat mtime mtime file1 stat size ೋΞΫηεͯͯ͠ޮ͕ѱ͍… file1 ͷ size ΛऔΓग़͢ॲཧΛՃ
ਖ਼͍͠ॱংͰɺ͔ͭޮྑ͘ॲཧͰ͖Δ ίʔυΛॻ͖͍ͨɻ file1 file2 file3 stat mtime stat stat mtime
mtime size ֤ϑΝΠϧҰ͚ͩΞΫηε͢Δ file1 ͕औಘͰ͖ͨΒશͯͷstat ͕ἧͬͯͳͯ͘ॲཧ͢Δ
੍݅Λ͖ͪΜͱ ຬͨ͢ίʔυΛ ॻ͘ͱ͜͏ͳΔ
var paths = ['file1.txt', 'file2.txt', 'file3.txt'], file1 = paths.shift(); async.parallel([
function(callback) { fs.stat(file1, function(error, stat) { // stat.size Λ͏ callback(error, stat); }); }, function(callback) { async.map(paths, fs.stat, callback); } ], function(error, results) { var stats = [results[0]].concat(results[1]); // stats Λ͏ }) Oh...
• ॲཧΛϞδϡʔϧԽͨ͠ΓΈཱͯͨΓ͢Δͷ͕͍͠ɻ • ஞ࣍ॲཧ͔ฒྻॲཧ͔Λ໌ࣔతʹ੍ޚ͢Δඞཁ͕͋Δɻ • ਖ਼͘͠ಈ͘ίʔυΛॻ͘ͷ͕େมɻ • ઃܭͷҙਤ͕໌֬Ͱͳ͘ϝϯςφϯεੑ͕͍ɻ • ॲཧͷ࣮ߦઓུʢஞ͔࣍ฒྻ͔ʣ࣍ୈͰɺޙଓͷλεΫΛ
Ճ͢Δํ๏͕มΘͬͯ͠·͏ɻ
ίʔϧόοΫ vs. ϓϩϛε
ϓϩϛεͱ • ”ྃͯ͠ͳ͍͔͠Εͳ͍ܭࢉ”ͷ݁ Ռ͕ೖͬͯΔശɻ • ϓϩϛεࣗମͳͷͰɺؔͷؒͰ ड͚͠Ͱ͖Δɻ • ܭࢉ͕ྃ͢ΔͱಛఆͷॲཧΛݺͼग़ ͯ͘͠ΕΔػೳΛ࣋ͭ߹͕ଟ͍ɻ
var p1 = new Promise(); p1.then(console.log); ... p1.resolve(42); ϓϩϛε͕ղܾ͞Εͨ࣌ ʹݺͿؔΛొ
ϓϩϛεΛղܾ͢Δ 㱺 ͜͜Ͱ console ʹ “42” ͕ग़ྗ͞ΕΔ
ͱ͜ΖͰ…
ͱ͍͏λΠτϧͰ͕͢ ͯ͢ͷϓϩϛε͕ ؔܕͳΘ͚Ͱ͋Γ·ͤΜ
ݴޠϥΠϒϥϦʹΑͬͯେ͖͘ػೳ͕ҧ͏ • Πϕϯτ௨ػೳ͕͋Δ͔ • ߹Ͱ͖Δ͔ • ಡΈࠐΈઐ༻දݱ͕͋Δ͔ • ΤϥʔϋϯυϦϯάͰ͖Δ͔ ໊લ༷ʑ:
• Future • Promise • Deferred • I-var • …
ϓϩϛε × ؔܕ
ؔܕͬͯͳ͋ʹʁ
ؔܕϓϩάϥϛϯά ͋ΒΏΔͷΛͱͯ͠ ѻ͏͜ͱͰΛղ͘ख๏ ʹ ”ࣜࢦ”ͱݺΕΔ
໋ྩܕϓϩάϥϛϯά • Ͳ͏Δ͔ (how) Λɺ໋ྩγʔέϯεΛ໌ࣔతʹهड़ ͯ͠Ϛγϯʹ͑Δɻ ؔܕϓϩάϥϛϯά • ԿΛͯ͠΄͍͔͠ (what)
Λ”ಉ࢜ͷؔ”ʹΑͬͯه ड़͠Ϛγϯʹ͑Δɻ • ίϯϐϡʔλ”ಉ࢜ͷؔ”͔Β໋ྩγʔέϯεΛ ܭࢉ͢Δɻ
ؔ ಉ࢜ͷґଘؔΛ දݱ͢Δಓ۩ ʹ
function func(in) { return /* in ͔Β out Λܭࢉ */;
} out = func(in) ”out in ʹґଘ͍ͯ͠Δ”ͱಡΊΔ ؔ Λೖྗͯ͠ɺมͯ͠ɺΛग़ྗ͢Δ ग़ྗೖྗʹʢͷΈʣґଘ͢Δ ʹ
ෳͷؔΛ߹ͯ͠ ΑΓେ͖ͳؔΛ࡞Δ
ؔͷग़ྗΛ ผͷؔͷೖྗͱܨ͛ͯ ॲཧͷύΠϓϥΠϯΛ࡞Δ function f(in) { return /* in ͔Β
out Λܭࢉ */ } function g(in) { return /* in ͔Β out Λܭࢉ */ } out = g(f(in)) f ͷग़ྗΛ g ʹೖྗ͢Δ ಉ༷ʹ”out in ʹґଘ͍ͯ͠Δ”ͱಡΊΔ
ؔܕϓϩάϥϛϯά •͋ΒΏΔͷΛ””ͱͯ͠ѻ͏ɻ •ಉ࢜ͷґଘؔΛ”ؔ”Ͱදݱ͢Δɻ •ෳͷؔΛ߹ͯ͠ΑΓେ͖ͳؔΛ࡞Δɻ ʹ
ϓϩϛε × ؔܕ •͋ΒΏΔϓϩϛεΛ””ͱͯ͠ѻ͏ɻ •ϓϩϛεಉ࢜ͷґଘؔΛ”ؔ”Ͱදݱ͢Δɻ •ෳͷඇಉظܭࢉΛ߹ͯ͠ΑΓେ͖ͳඇಉظܭ ࢉΛ࡞Δɻ ʹ
ϓϩϛεΛͬͯΈΔ
var fs_stat = promisify(fs.stat); var paths = ['file1.txt', 'file2.txt', 'file3.txt'];
var statsPromises = paths.map(fs_stat); file1 file2 file3 stat stat stat fs_stat ݁Ռϓϩϛε ͱ͍͏ശʹೖΔ String ͷྻ͔ΒϓϩϛεͷྻΛ࡞Δ
// promisify :: (a -> (Error -> b -> ())
-> ()) -> (a -> Promise b) var promisify = function(fn, receiver) { return function() { var slice = Array.prototype.slice, args = slice.call(arguments, 0, fn.length - 1), promise = new Promise(); args.push(function() { var results = slice.call(arguments), error = results.shift(); if (error) promise.reject(error); else promise.resolve.apply(promise, results); }); fn.apply(receiver, args); return promise; }; } ίʔϧόοΫ൛͔Βϓϩϛε൛Λ࡞Δϔϧύʔؔ
ผͷॲཧΛ ͚Ճ͍͑ͨ࣌ʁ
var statsPromises = paths.map(fs_stat); statsPromises[0].then(function(stat) { /* stat.size */ });
then() Λ͏ͱϓϩϛεʹґଘ͢Δ ผͷඇಉظॲཧΛهड़Ͱ͖Δ file1 stat size ϓϩϛεΛ࡞Δ fs_stat then(function(stat)->...) ശ͔ΒΛऔΓग़͠ ؔʹ༩͑Δ
then() ඇಉظܭࢉͷ݁ՌΛλΠϛϯάඇ ґଘͰѻ͑Δɻthen() ʹ͞ΕΔؔɺ • ͕͍ͭར༻ՄೳʹͳΔ͔ • λεΫΛͲΜͳॱ൪Ͱॲཧ͢Δ͔ Λؾʹ͢Δඞཁ͕ͳ͍ɻ
ϓϩϛεͱ then() Λ͏ͱ… • ίϯϐϡʔλɺهड़͞ΕͨґଘؔΛ ݩʹ࣮ߦॱংΛࣗಈతʹܾఆ͢Δɻ • ख࡞ۀͰ੍ޚϑϩʔΛॻ͘ඞཁ͕ͳ͍ʂ
Ϧετʹର͢Δ ϓϩϛε
શͯͷ stat ͕ἧ͔ͬͯΒॲཧ͍ͨ͠… file1 file2 file3 stat mtime stat stat
mtime mtime ݁Ռ͕ἧ͏ͷΛ͍ͪͨ
stat mtime stat stat mtime mtime ”ϓϩϛεͷϦετ”Λ ”Ϧετʹର͢Δϓϩϛεʹ”ม stat stat
stat var statsPromises = paths.map(fs_stat); list(statsPromises).then(function(stats) { /* stats */ }); ͪ߹Θ͕ͤՄೳʹʂ list() then()
// list :: [Promise a] -> Promise [a] var list
= function(promises) { var listPromise = new Promise(); for (var k in listPromise) promises[k] = listPromise[k]; var results = [], done = 0; promises.forEach(function(promise, i) { promise.then(function(result) { results[i] = result; done += 1; if (done === promises.length) promises.resolve(results); }, function(error) { promises.reject(error); }); }); if (promises.length === 0) promises.resolve(results); return promises; }; ϓϩϛεͷϦετʹ then() ΛՃ͢Δϔϧύʔؔ
·ͱΊΔͱ…
var fs_stat = promisify(fs.stat); var paths = ['file1.txt', 'file2.txt', 'file3.txt'],
statsPromises = list(paths.map(fs_stat)); statsPromises[0].then(function(stat) {/* stat.size Λ͏ */}); statsPromises.then(function(stats) {/* stats Λ͏ */}); file1 file2 file3 list(paths.map(fs_stat)) stat stat stat size mtime mtime mtime ґଘؔͷهड़ͷΈͰ ஞ࣍ॲཧฒྻॲཧ࣮ݱͰ͖͍ͯΔʂ
A. λεΫಉ࢜ͷґଘؔΛߟ͑Δɻ B. ඞཁͳૢ࡞ͷॱংΛߟ͑Δɻ C.BΛ࣮ݱ͢Δ੍ޚϑϩʔΛॻ͘ɻ ϓϩϛεΛ͏ͱɺίϯϐϡʔλ͕ A ͔Β࠷దͳ C Λಋग़ͯ͘͠ΕΔʂ
ϓϩϛε͍͠ʁ
Mikeal Rogersࢯͷ • ”ϓϩϛεΛͬͨ API ɺͦΕ͕Ͳ͏ ಈ࡞͢Δ͔ΛௐΔඞཁ͕͋Δɻ” • ”then()
list() ҙຯΛӅṭ͢Δͷ Ͱɺೝతෛՙ͕େ͖͍ɻ” from http://www.futurealoof.com/posts/broken-promises.html
James Coglanࢯͷ࠶ • ”ϓϩϛε͕ easy Ͱ͋Δ͔ॏཁͰͳ ͍ɻsimple Ͱ͋Δ͔Λ͏͖ɻ” • ”Γ͍ͨ͜ͱ͕มΘͬͨ࣌ʹίʔυͷ
มߋ͕গͳ͘ࡁΉɻϓϩϛεɺίϨ Ϋγϣϯඇಉظੑ࣮ߦॱংͱ͍ͬ ͨ֓೦ͱͰ͖Δ͔Βͩɻ” from http://blog.jcoglan.com/2013/04/01/callbacks-promises-and-simplicity/
ʢࢲͷҙݟʣ • ”ίετͷࢧ͍Λੵۃతʹ༛༧ͭͭ͠ ίʔσΟϯάͰ͖Δ”͜ͱϓϩτλΠ ϐϯάͰॏཁͳੑ࣭ɻ • ίετͱϝϦοτΛఱṝʹ͔͚Δɻ • ͨͩɺඇಉظϓϩάϥϛϯάͷ”ίετ ͷࢧ͍ظݶ”ҙ֎ͱૣ͍ͷͰʁ
͓Ͱ͖ͳ͔ͬͨࣄ • Ϧετॲཧ (reduce) ͱͷΈ߹Θͤ • ԆϓϩϛεʹΑΔґଘੑղܾ • Promises/A+ ͱϞφυ
• Fantasy Land ͔Β Real World
• ίʔϧόοΫ࣮ߦॱংΛ໌ࣔ͢Δͷ Ͱͱ͖͍ͬͭ͢ɻ • มߋʹڧ͘ɺϞδϡϥʔͳϓϩάϥϜ Λॻ͖͍ͨͳΒϓϩϛε͕͓קΊɻ • ੍ޚϑϩʔػցʹߟ͑ͤ͞Α͏ʂ ·ͱΊ
ϝοηʔδ • ؔܕɺษڧͯ͠Έ·ͤΜ͔ʁ • ྫ͑ࣄͰΘͳͯ͘ɺϓϩάϥϚ ͱͯܳ͠෩Λ͛Δͷʹେ͍ʹཱͭ ͱࢥ͍·͢ɻ
ࢁຊ, ”ؔϓϩάϥϛϯά͕ڭ͑ͯ͘ΕΔن” ؾܰʹֶΜͰΈ͍ͨਓ͚:
Miran Lipovaa, “͍͢͝Haskellͨͷֶ͘͠΅͏!”ʢΦʔϜࣾʣ ΨνͰΓ͍ͨਓ͚: