book

Clojure Programming Cookbook

Name: Clojure Programming Cookbook
ISBN: 9781785885037

by Makoto Hashimoto, Nicolas Modrzyk

October 2016

Intermediate to advanced

618 pages

10h 44m

English

Packt Publishing

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Clojure Programming Cookbook
Clojure Programming Cookbook
Credits
About the Authors
About the Reviewer
www.PacktPub.com
eBooks, discount offers, and moreWhy subscribe?
Preface
What this book covers
What you need for this book
Who this book is for
Sections
Getting readyHow to do it…How it works…There's more…See also

Conventions
Reader feedback
Customer support
Downloading the example codeDownloading the color images of this book ErrataPiracyQuestions
1. Live Programming with Clojure
Introduction
REPL up!
Getting readyHow to do it...How it works...There's more...See also
Working with primitive data types
Getting readyHow to do it...Using numbersUsing strings and charactersUsing booleans and nilUsing symbols and keywordsHow it works...There's more...
Using bindings of vars, conditions, loops, and error handling
Getting readyHow to do it...def and letif and if-notwhen and when-notcase and conddo and dotimesloop and recurtry... catch... throwHow it works...
Using and defining functions
Getting readyHow to do it...Defining simple functionsDefining variadic functionsDefining multiple arity functionsDefining functions that specify arguments using a keywordDefining functions with pre-condition and post-conditionHow it works...There's more...
Using third-party libraries
Getting readyHow to do it...Adding the JAR file manually to your classpathUsing Leiningen and a project.clj fileViewing dependenciesone-offNew dependencies at runtime
Using namespaces
Getting readyHow to do it...Creating a new namespaceInspecting namespacesAdding functions with :import and :referLoading namespaces from filesReloading namespacesHow to organize namespacesThere's more...Namespace for public APItools.namespace
What's next?
2. Interacting with Collections
Introduction
Clojure collections and their basic functions
Getting readyHow to do it...ListsVectorsMapsSetsHow it works...Clojure collectionsDifferences between lists and vectorsClojure is immutableThere's more...Converting collections between different typesUsing distinct
Accessing and updating elements from collections
Getting readyHow to do it...Accessing collections using the nth functionAccessing maps or sets using getMaps, sets, and keywords are functions to access collectionsAccessing a collection using second, next, ffirst, and nfirstUsing update to update collectionsHow it works...There's more...Using get for vectorsUsing collections as keys in mapsUsing get-inUsing assoc-inUsing update-in
Filtering elements from collections
Getting readyHow to do it...Filtering multiples of threeFiltering items of a mapFiltering non-nil valuesRemoving odd values from a sequenceUsing keepUsing keep-indexedThere's more...Filter as a transducerFiltering with core.async
Transforming and sorting collections
Getting readyHow to do it...Using built-in sortMigrating to sort-byUsing sorted-setWorking with sorted collection subsetsSorting Clojure mapsSorted map structureAre you sorted yet?How it works...There's more...Sorting lines of a file
Merging and splitting collections
Getting readyHow to do it...Using merge and merge-with for mergingThe zipmap merges keys and values for mapsUsing interleaveUsing split-at and split-with to split collectionsHow it works...There's more...Using group-by to split collectionsUsing the filter function to split collections
How to become lazy
Getting readyHow to do it...The iterate functionRealized?Random sequences with repeatedlyUsing the macro lazy-seqHow it works...There's more...Other lazy-seq-producing functionsForce evaluation with doallLazy evaluation with filesThe map function and calling rest
3. Clojure Next
Introduction
Using destructuring techniques
Getting readyHow to do it...Sequential destructuringUsing map destructuringHow it works...There's more...Sequential destructuring for stringConditional destructing with core.match
Using functional programming style
Getting readyHow to do it...Functions taking functions as their argumentsmapreduceapplyUsing anonymous functionsAnonymous functions using fnUsing function literals to define anonymous functionsFunctions returning functionsconstantlycomplementpartialcompevery-pred and some-fnHow it works...Clojure functions are first-class functionsPure functionsThere's more...reduce and applyloop and recur
Using threading macros
Getting readyHow to do it...Introducing the -> macroIntroducing the ->> macroIntroducing the cond-> and the cond->> macrosIntroducing some-> and some->>How it works...There's more...Introducing as->Flambo preview
Defining simple macros
Getting readyHow to do it...Your first macroYour second macroHow it works...There's more...Using quotesMacros everywhere
Defining more advanced macros
Getting readyHow to do it...Tracking when code was startedLogging a message with macroHow it works...There's more...deftest
Using protocols
Getting readyHow to do it...Defining a recordDefining a typeDefining a protocolHow it works...Records and types are Java classesDifferentiating between records and typesThere's more...Defining a mutable protocol and type
Defining multimethods
Getting readyHow to do it...Defining a multimethodHow it works...There's more...
Transducers for dummies
Getting readyHow to do it...How it works...Composable functionsInserting elementsWriting your own transducersShort circuitThere's more...Transducers with core.asyncSumming things up
Logic programming in Clojure
Getting readyBaby logic stepsGetting to know the "o" vocabularyconso: check for vector associationresto: check for the rest of a vectormemberoappendo: appending listcondeMatcheBeginner logicKeeping freshFinding only one resultMature logicRange of valuesHow to do it...Generating dataGenerating more data with more logic variablesUsing a projectHow it works...There's more...Validating the results of a functionWorking with external data
4. File Access and the Network
Introduction
Manipulating files and directories
Getting readyHow to do it...spit and slurpReader and writer with with-openCreating a file and directoryCopying a fileDeleting a file and a directoryListing files and directories in a directoryHow it works...slurp and spitwith-open macroThere's more...Reading HTTP resourceExamining the source code
Manipulating various formats of files - XML, JSON, YAML, and EDN
Getting readyHow to do it...XMLJSONYAML isn't a markup languageMessagePack, Clojure libraryHow it works...There's more...Extensible Data Notation
Making use of Clojure HTTP client
Getting readyHow to do it...How it works...There's more...async HTTP and core async
Using queues and topics in the RabbitMQ
Getting readyInstalling RabbitMQHow to do it...Producing hello world messages and consuming themDeclaring the namespace and loading Langohr libraries and IP address of the Docker containerDefining a producer functionDefining a message handler and consumerTesting producer and consumerUsing blocking consumerHow it works...Connect to broker and open channelHow producer worksDeclaring queueProducing messagesHow consumer worksConsumer messagesDefining message handlerThere's more...Using fanout exchangefanout-producerfanout-consumerRunning the fanout consumersTesting fanout consumersUsing topic exchangeTopic-publisherTopic-consumerRunning the topic consumersTesting the topic consumersSee also
Using Kafka
Getting readyDownloading Kafka 0.8.2.2Start ZooKeeper and Kafka serverCreate topicRun a console consumerUsing clj-kafkaHow to do it...Declaring the namespace and load Clojure libraryProducing messagesConsuming a messagesHow it works...Producing messagesConsuming messagesThere's more...Creating a new topicSee also
Using MQTT
Getting readyInstalling the MQTT brokerMQTT graphical clientSend our first MQTT messageGetting some ClojureHow to do it...How it works...There's more...
Streaming access to provide high performance
Getting readyHow to do it...Streaming outStreaming inStreaming with line-seqHow it works...There's more...
Using Apache Camel to connect everything
Getting readyHow to do it...Importing Camel classesYour first ride on Camel with ClojureWriting more Clojure idiomatic code with CamelHow it works...There's more...See also
5. Working with Other Languages
Introduction
Calling Java methods and accessing Java objects from Clojure
Getting readyHow to do it...Instantiating objectsCalling instance methodsCalling class methodsAccessing instance fieldsAccessing class fieldsAccessing inner classesReferencing classesUsing arraysHow it works...Summary of how Clojure accesses Java methods and objectsClojure does not inherit Java's checked exceptionSummary of array accessesPrint strings of Java's primitivesThere's more...Chained calls with the double-dot macroUsing the doto macroUsing reflections
Extending Java superclasses and implementing Java interfaces
Getting readyHow to do it...Using proxyUsing reify for implementing interfacesHow it works...There's more...Defining anonymous classes in ClojureUsing annotations
Calling Clojure from Java
Getting readyHow to do it...Defining a simple named class using gen-classDefining a class with instance methods and constructors in ClojureCreating a JAR file callable from JavaHow it works...The project.clj for generating Java classesAOT compilationThere's more...Defining an interface and implementing a class callable from JavaUsing Maven for Clojure and Java projects
Calling Scala from Clojure
Getting readyHow to do it...Using Leiningen to develop Scala and ClojureImporting Scala classesCalling instance methodsCalling singleton methodsAccessing tuplesAccessing Scala fieldsHow it works...There's more...Using SBTCreating an SBT-based projectWriting source code
ClojureCLR
Getting readyInstalling Visual Code Studio and creating a projectInstalling Mono Studio IDELein CLRHow to do it...Calling .NET code from ClojureStarting an REPLWorking with IOParsing some XML using C# codeCalling a REST API using Clojure/C#UI PrototypingPutting it all togetherHow it works...Compiling Clojure code for .NETAdding Clojure code to a Visual Studio projectRunning Clojure code using Clojure.RTUsing Xamarin Mono StudioThere's more...
ClojureScript
Getting readyHow to do it...Autocompiling your codeFibonacci'edHow it works...Interacting with JavaScriptUsing jQuery from ClojureScriptCreating a ClojureScript libraryUsing a third-party libraryThere's more...Running in the REPLCompiling code for both Clojure and ClojureScript
6. Concurrency and Parallelism
Introduction
Solving concurrent problems using Clojure
Getting readyHow to do it...Using atomsCreating and referring atomUpdating atomUsing validatorUsing CAS operationSoftware Transactional Memory using ref and dosyncCreating refUpdating refs using alterUsing ensureUsing watcher and a refined transaction codeUsing commuteUsing agentsCreating agentsUpdating agentsHow it works...Summary of three reference types in ClojureCoordinated/uncoordinatedSynchronous/asynchronousHow STM works in ClojureAlter and commuteThere's more...promise and deliverpmap, pcalls, and pvaluespcallspvaluesSee also
Distributed actor-based dev with Akka
Getting readyHow to do it...Your first okkuCreating actorsDispatching messagesHow it works...Actor systemUnderstanding actorsThere's more...Calling remote actorsRequest and replySee also
Using Spyglass and Couchbase to share state between JVMs
Getting readySetting up dependencies in project.cljSetting up Couchbase Server as a Memcached serverUsing docker-compose to start Couchbase ServerCreating a directory and a file for docker-composeStart Couchbase clusterCheck if Docker processes are runningSummary of Couchbase clusterUsing Couchbase web administrator consoleLogging into the web consoleAdding nodes to the clusterAdding ClusterDefining Memcached bucketHow to do it...Defining to use Spyglass libraryConnecting serverSet valuesGet values from another REPLTesting time to liveDisconnectingHow it works...What is Memcached?Access Memcached from TelnetCouchbase ServerThere's more...Using get-multiUsing async-getUsing CAS operationsSee also
Reactive programming with meltdown
Getting readyHow to do it...Defining a reactorSending a message to a reactorGoing the sync wayHow it works...SelectorsStreamsStreams and reduceCombining functions with a graphCustom streamsThere's more...
Bridging core.async
Getting readyMemories - reviewing core.async basicsPub/subHow to do it...Async socket serverAsync socket clientChimingThere's more...Client to Python WebSocketsClojure WebSocket server
On Quasar/Pulsar
Getting readyHow to do it...How it works...Watching over other actors lifecyclesState of an actorThere's more...Blazar
7. Advanced Tips
Introduction
Hacking the Clojure code
Getting readyHow to do it...How it works...There's more...
Using Reader Conditionals, compile to Clojure, and ClojureScript
Getting readyHow to do it...Your first Reader ConditionalUsing Reader Conditionals in namespacesHow it works...The form of Reader Conditionals and Splice macrosMacros in ClojureScriptThere's more...Building an application for Clojure and ClojureScriptAdding a cljc file for demonstrating QuilTesting cljc code in both Clojure and ClojureScriptBuilding and running a demoSee also
Real-time shared development with an REPL
Getting readyHow to do it...Shared REPLsUsing Atom and proto-replUsing an embedded NREPLThere's more...Custom REPL using Java interopServerClientThe async custom REPL serverServer REPL or more on real-time work on production code
Declarative data descriptions and validations with plumatic/schema
Getting readyHow to do it...My first schemaUsing schema for records and other typesDefining functions with validationsHow it works...Performance considerationsGenerating test dataThere's more...Data coercion with prismatic/schemaUsing core.typedcore.spec
8. Web Applications
Introduction
Clojure with Vaadin - easy web widgets
Getting readyProject settingsThe Clojure/Vaadin flowHow to do it...Using the Calendar widgetReacting to eventsClicking a buttonUsing and reloading namespacesServer-side pushThere's more...Reactive Vaadin - ideasReactive Vaadin - CPU monitoringReactive Vaadin - Telegram on Raspberry PiDeployment bonus
Quickly create a REST API with Liberator
Getting readyHow to do it...Your first LiberatorUsing defresourceParameterized resourcesDefining GET/POST/PUT/DELETE methods for REST APIsHow it works...Methods and status codes of HTTPTracing requestsThere's more...Persistent REST resources using clojure.java.jdbcPreparing for jdbcOur service specCreating a product table and defining access functionsDefining resources and starting a serverAccessing from an HTTP client
Working with Immutant - reusing infrastructure
Getting readyHow to do it...Simple messaging with ArtemisRemote messagingRemote procedure call with queuesScheduling code executionPiping and defining data transformation pipelinesUsing WebSockets made easyThere's more...Packaging as standalonePackaging as a deployable web archive (WAR file)
Developing with om.next, the next-generation ClojureScript library
Getting readyCreating a new project for om.nextUpdating the om versionTips for dependenciesStarting figwheelHow to do it...Getting started with om.nextUsing statesHow it works...React fundamentalsdefuireconcilerLife cycle of componentsThere's more...Task list using om.nextDefining the namespace and libraries to useDefining stateDefining readDefining mutateDefining UIs
9. Testing
Introduction
Behavior-driven development
Getting readyDependenciesThe first featureDesigning a folder structure to organize featuresHow to do it...Many assumptions with tablesReading assumptions from a CSV fileDoing it with ExcelDoing it with web APIs and MongoDBThere's more...VirtualBoxFreactiveFlambo, or BDD meets Apache SparkEEP for BDDOpenCV
Testing with random inputs and pattern-based testing
Getting readyLibrariesGenerating random values or groups of valuesRandom values based on schemaHow to do it...Your first test.check specificationAuto-running testsMore specifications and generatorsGenerators and de-structuringHerbertThere's more...
Benchmarking with Criterium, performance tips, and other tools
Getting readyHow to do it...Using CriteriumHow it works...Type hintsUsing appropriate data typesMaps versus records versus typesPrimitive arraysWorking with transient data structuresMemoize functionsThere's more...Logging with timbre and profiling with tufteUsing jvisualvm
10. Deployment and DevOps
Introduction
Riemann - monitoring deliverance and slacking
Getting readyInstalling the Riemann serviceConfiguring the Riemann daemonThe Riemann dashboardRiemann-healthJust enough dashboard configurationPreparing to send eventsHow to do it...Basic event reporting for a serviceExpiring eventsHow it works...There's more...From Riemann to Slack webhooksFrom Slack bots to Riemann
Deploying Clojure with Docker
Getting readyInstalling Docker on OS X or WindowsInstalling Docker on DebianPreparing the Clojure applicationPackaging the application into a JAR fileCreating the Docker containerHow to do it...Connecting directly to a remote DockerThere's more...
Clojure on Amazon Web Services
Getting readySigning up on AWSGetting the access key and secret access keySetting up dependencies in your project.cljHow to do it...Using EC2Using S3Using Amazon SQSServerless Clojure with AWS LambdaClojure namespace helloworldHello World - the AWS partHello StreamReal-world LambdasHow it works...What is Amazon EC2?Amazon S3Buckets and keysObjectsThere's no more...

Content preview from Clojure Programming Cookbook

Accessing and updating elements from collections

In this recipe, we will teach you how to access elements and update elements in collections.

Getting ready

You only need REPL, as described in the recipe in Chapter 1, Live Programming with Clojure, and no additional libraries. Start REPL so that you can review the sample code in this recipe.

How to do it...

Let's start with accessing collections.

Accessing collections using the nth function

nth gets the n^thelement from collections. The second argument of nth starts from 0 and throws an exception if the second argument is larger than the number of elements minus 1:

(nth [1 2 3 4 5] 1) ;;=> 2 (nth '("a" "b" "c" "d" "e") 3) ;;=> "d" (nth [1 2 3] 3) ;;=> IndexOutOfBoundsException clojure.lang.PersistentVector.arrayFor ...

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