Real World PureScript

RealWorldPureScript(Day1) JustinWoo MonadicParty-2019Jun20 1/21

Plan Day1:WhatisPureScript,andhowdothesetypeswork? IntroducethePureScriptlanguage,talkaboutsomedetailswithtypes,kinds,typeclasses+functional dependencies,andthewhyandhowofrowtypesandrowtypeclasses. Day2:HowdowedoFFI,andhowcanweusetypestomakeitbetter? IntroduceFFIinPureScript,andvariousapproachestoFFIwithtypes,frombasicopaquedatatypesto datatypeswithrowtypeparameters. https://github.com/justinwoo/real-world-purescript-workshop-2019
2/21

PreviewofDay1contents Typealiases,newtypes,datatypes Functions,patternmatching,guards Anonymousrecords Typeclasseswithmultipleparametersandfunctionaldependencies Kinds,Rowkind Recordsasatypewitharowtypeparameter Rowtypeclasses 3/21

Setup Youwillneed... PureScript0.13.0 Spago Node10.xorhigher Installationmethods: ViaNix:https://github.com/justinwoo/easy-purescript-nix Vianpm:npmi-gpurescriptspago Please,makesureyouhavesetnpmpreﬁxtosomethinglike~/.npm: #~/.npmrc
prefix=/home/your-user/.npm npmsetprefix~/.npmrc 4/21

WhatisPureScript? aHaskell-likelanguageforworkingwithJavaScript alanguageforusingtypesforbothstaticguaranteesandautomaticallyderivedroutines astateofmind asourceofmemesonTwitter "therowtypeslanguage" 5/21

Helloworld(src/Main.purs) Helloworld: moduleMainwhere --moduleMain(main)where importPrelude importEffect(Effect) importEffect.Console(log) main::EffectUnit main=do log"Hellosailor!"
>spagorun 6/21

Types(src/Basics.purs) typeStringAlias=String stringAliasValue::StringAlias stringAliasValue="Hello" newtypeURL=MkURLString urlValue::URL urlValue=MkURL"https://google.com" dataURLorCode =IsURLString |IsCodeString
urlOrCodeValue::URLorCode urlOrCodeValue=IsCode"banana" 7/21

Functions unwrapURL::URL->String unwrapURL(MkURLs)=s isCode::URLorCode->Boolean isCode(IsCode_)=true isCode(IsURL_)=false isCode'::URLorCode->Boolean isCode'x=casexof IsCode_->true _->false
isCode''::URLorCode->Boolean isCode''x |IsCode_<-x=true |otherwise=false 8/21

AnonymousRecords UnlikeHaskell: typeMyRecord= {apple::String ,banana::String ,kiwi::String } Moreonthisaftertalkingabouttypes,Types,rowtypes,andkinds. 9/21

TypeClasses (src/TypeClassesAndKinds.purs) Givensomeconcretetype,youshouldbeabletomatchsomeinstance,whichmayleadto additionaltypesbeingdetermined additionalfunctionsbeingdetermined classUnwrapta|t->awhere unwrap::t->a instanceunwrapURLInstance::UnwrapURLStringwhere unwrap(MkURLs)=s
10/21

classRodeoTypesinputoutput|input->output instancerodeoIntString::RodeoTypesIntString instancerodeoStringBoolean::RodeoTypesStringBoolean dataProxys=Proxy rodeoTypes::forallinputoutput .RodeoTypesinputoutput =>Proxyinput->Proxyoutput rodeoTypes_=Proxy rodeoResult1::ProxyString rodeoResult1=rodeoTypes(Proxy::ProxyInt)
rodeoResult2::Proxy?hole--Hole'hole'hastheinferredtypeBoolean rodeoResult2=rodeoTypes(Proxy::ProxyString) 11/21

Kinds Sofar,everythinghashadinferredkinds,typicallyofkindType. dataProxy(s::Type)=Proxy AllTypeshavevalues,buthowaboutsomethatdon't?e.g.Symbolkind: --fromData.Symbol dataSProxy(sym::Symbol)=SProxy --Informationissimplyusedincompiletime: staticStringProxy::SProxy"helloworld" staticStringProxy=SProxy --fromData.Symbol
classIsSymbol(sym::Symbol)where reflectSymbol::SProxysym->String reflectedSymbolValue::String reflectedSymbolValue=reflectSymbolstaticStringProxy 12/21

Arrowkind ->takestwoTypesandgivesyouaType. typeIntToInt1=Int->Int typeArrow=(->)::Type->Type->Type typeFromInt=(->)Int::Type->Type typeIntToInt2=FromIntInt::Type 13/21

Rowkind(src/Rows.purs) Specialsymbol#,whichcancreatearowofatypeofakind. "Row":unorderedcollectionofﬁeldsbySymbolandassociatedtypeofakind. typeEmptyRow=()::#Type typeSingleRow=(a::String)::#Type typeSymbolRow=(a::"apple")::#Symbol Enablesuser-createddatatypes,e.g.polymorphicvariantsasalibrary:purescript-variant foreignimportdataVariant::#Type->Type 14/21

Records --fromPrim("builtins") dataRecord::#Type->Type typeMyRecordA= {apple::String ,banana::String } typeMyRecordB= Record (apple::String
,banana::String ) id=identity::MyRecordA->MyRecordB fn1::MyRecordA->String fn1r=r.apple fn1::MyRecordA->MyRecordA fn1r=r{apple="no"} 15/21

Rowtypeclasses WhatifwecouldusetherowtypeparameterofRecordandbeabletogetgenerictype-levelinformation? --Built-intypeclassesin`Prim.Row` classUnion(left::#Type)(right::#Type)(union::#Type) |leftright->union ,rightunion->left ,unionleft->right classNub(original::#Type)(nubbed::#Type) |original->nubbed classLacks(label::Symbol)(row::#Type)
classCons(label::Symbol)(a::Type)(tail::#Type)(row::#Type) |labelatail->row ,labelrow->atail 16/21

PureScript-Record purescript-recordisalibrarywhichusesexactlytheseconstraintstoextracttypeinformation. get::forallrr'la .IsSymboll =>Row.Conslar'r =>SProxyl->{|r}->a get=--... result::?hole--Hole'hole'hastheinferredtypeInt result=get(SProxy::_"apple"){apple:123} insert::forallr1r2la
.IsSymboll =>Lackslr1 =>Conslar1r2 =>SProxyl->a->{|r1}->{|r2} 17/21

ReviewofDay1contents Typealiases,newtypes,datatypes Functions,patternmatching,guards Anonymousrecords Typeclasseswithmultipleparametersandfunctionaldependencies Kinds,Rowkind Recordsasatypewitharowtypeparameter Rowtypeclasses 18/21

Extrareading Generics-Rep(DatatypeGenerics)tutorialhttps://purescript-simple- json.readthedocs.io/en/latest/generics-rep.html AtutorialofhowtouseDatatypeGenericsinPureScript,whichallowyoutoworkwithageneric representationoftypeswhicharederivedbythecompiler,sothatyoucanwriteaseriesoftypeclasses thatworkforalldatatypesderivingmethodsofgenericrepresentations. "TypeclassesandInstancesarePatternMatchingforTypes"https://github.com/justinwoo/my- blog-posts/blob/master/posts/2018-04-27-type-classes-and-instances-are-pattern-matching-for- types.md
Ageneralpostabouthowworkinginthetypelevelhasmanyparallelstoworkinginthevaluelevel,with discussionofRowToList. 19/21

Humor "FunTypeLevelliteralnumberarithmeticwithInstanceChains"https://github.com/justinwoo/my- blog-posts/blob/master/posts/2018-05-27-fun-type-level-literal-number-arithmetic-with-instance- chains.md classAdd(l::Symbol)(r::Symbol)(o::Symbol)|l->ro instancezeroAdd::Add"zero"rr elseinstancesuccAdd:: (Succl'l ,Succrr' ,Addl'r'o
)=>Addlro "Wedon'tneedPeanoNumbersinPureScript"https://github.com/justinwoo/my-blog- posts/blob/master/posts/2018-09-11-we-dont-need-peano-numbers-in-purescript.md resultSub2::SProxy"....................................." resultSub2= T.sub(SProxy::SProxy"...............................................")(SProxy::SProxyT.Ten) 20/21

Somememes https://twitter.com/jusrin00/status/1012327213591605249 https://twitter.com/jusrin00/status/933428832618545153 https://twitter.com/jusrin00/status/963892030773579776 https://twitter.com/jusrin00/status/1082058122393513984 https://twitter.com/jusrin00/status/1053763021208723456 https://twitter.com/jusrin00/status/985596999998328832 https://twitter.com/jusrin00/status/968471589812670465 https://twitter.com/jusrin00/status/1008330774884601856 https://twitter.com/jusrin00/status/1132007452810063874
https://twitter.com/jusrin00/status/1128059526404554752 https://twitter.com/jusrin00/status/1094190044175159296 21/21

Real World PureScript

Real World PureScript

Justin Woo

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