https://kotlinlang.org logo
Channels
100daysofcode
100daysofkotlin
100daysofkotlin-2021
advent-of-code
aem
ai
alexa
algeria
algolialibraries
amsterdam
android
android-architecture
android-databinding
android-studio
androidgithubprojects
androidthings
androidx
androidx-xprocessing
anime
anko
announcements
apollo-kotlin
appintro
arabic
argentina
arkenv
arksemdevteam
armenia
arrow
arrow-contributors
arrow-meta
ass
atlanta
atm17
atrium
austin
australia
austria
awesome-kotlin
ballast
bangladesh
barcelona
bayarea
bazel
beepiz-libraries
belgium
benchmarks
berlin
big-data
books
boston
brazil
brikk
budapest
build
build-tools
bulgaria
bydgoszcz
cambodia
canada
carrat
carrat-dev
carrat-feed
chicago
chile
china
chucker
cincinnati-user-group
cli
clikt
cloudfoundry
cn
cobalt
code-coverage
codeforces
codemash-precompiler
codereview
codingame
codingconventions
coimbatore
collaborations
colombia
colorado
communities
competitive-programming
competitivecoding
compiler
compose
compose-android
compose-desktop
compose-hiring
compose-ios
compose-mp
compose-ui-showcase
compose-wear
compose-web
confetti
connect-audit-events
corda
cork
coroutines
couchbase
coursera
croatia
cryptography
cscenter-course-2016
cucumber-bdd
cyprus
czech
dagger
data2viz
databinding
datascience
dckotlin
debugging
decompose
decouple
denmark
deprecated
detekt
detekt-hint
dev-core
dfw
docs-revamped
dokka
domain-driven-design
doodle
dsl
dublin
dutch
eap
eclipse
ecuador
edinburgh
education
effective-kotlin
effectivekotlin
emacs
embedded-kotlin
estatik
event21-community-content
events
exposed
failgood
fb-internal-demo
feed
firebase
flow
fluid-libraries
forkhandles
forum
fosdem
fp-in-kotlin
framework-elide
freenode
french
fritz2
fuchsia
functional
funktionale
gamedev
ge-kotlin
general-advice
georgia
geospatial
german-lang
getting-started
github-workflows-kt
glance
godot-kotlin
google-io
gradle
graphic
graphkool
graphql
graphql-kotlin
graviton-browser
greece
grpc
gsoc
gui
hackathons
hacktoberfest
hamburg
hamkrest
helios
helsinki
hexagon
hibernate
hikari-cp
hire-me
hiring
hongkong
hoplite
http4k
hungary
hyderabad
image-processing
india
indonesia
inkremental
intellij
intellij-plugins
intellij-tricks
internships
introduce-yourself
io
ios
iran
israel
istanbulcoders
italian
jackson-kotlin
jadx
japanese
jasync-sql
java-to-kotlin-refactoring
javadevelopers
javafx
javalin
javascript
jdbi
jhipster-kotlin
jobsworldwide
jpa
jshdq
juul-libraries
jvm-ir-backend-feedback
jxadapter
k2-early-adopters
kaal
kafka
kakao
kalasim
kapt
karachi
karg
karlsruhe
kash_shell
kaskade
kbuild
kdbc
kgen-doc-tools
kgraphql
kinta
klaxon
klock
kloudformation
kmdc
kmm-español
kmongo
knbt
knote
koalaql
koans
kobalt
kobweb
kodein
kodex
kohesive
koin
koin-dev
komapper
kondor-json
kong
kontent
kontributors
korau
korean
korge
korim
korio
korlibs
korte
kotest
kotest-contributors
kotless
kotlick
kotlin-asia
kotlin-beam
kotlin-by-example
kotlin-csv
kotlin-data-storage
kotlin-foundation
kotlin-fuel
kotlin-in-action
kotlin-inject
kotlin-latam
kotlin-logging
kotlin-multiplatform-contest
kotlin-mumbai
kotlin-native
kotlin-pakistan
kotlin-plugin
kotlin-pune
kotlin-roadmap
kotlin-samples
kotlin-sap
kotlin-serbia
kotlin-spark
kotlin-szeged
kotlin-website
kotlinacademy
kotlinbot
kotlinconf
kotlindl
kotlinforbeginners
kotlingforbeginners
kotlinlondon
kotlinmad
kotlinprogrammers
kotlinsu
kotlintest
kotlintest-devs
kotlintlv
kotlinultimatechallenge
kotlinx-datetime
kotlinx-files
kotlinx-html
kotrix
kotson
kovenant
kprompt
kraph
krawler
kroto-plus
ksp
ktcc
ktfmt
ktlint
ktor
ktp
kubed
kug-leads
kug-torino
kvision
kweb
lambdaworld_cadiz
lanark
language-evolution
language-proposals
latvia
leakcanary
leedskotlinusergroup
lets-have-fun
libgdx
libkgd
library-development
lincheck
linkeddata
lithuania
london
losangeles
lottie
love
lychee
macedonia
machinelearningbawas
madrid
malaysia
mathematics
meetkotlin
memes
meta
metro-detroit
mexico
miami
micronaut
minnesota
minutest
mirror
mockk
moko
moldova
monsterpuzzle
montreal
moonbean
morocco
motionlayout
mpapt
mu
multiplatform
mumbai
munich
mvikotlin
mvrx
myndocs-oauth2-server
naming
navigation-architecture-component
nepal
new-mexico
new-zealand
newname
nigeria
nodejs
norway
npm-publish
nyc
oceania
ohio-kotlin-users
oldenburg
oolong
opensource
orbit-mvi
osgi
otpisani
package-search
pakistan
panamá
pattern-matching
pbandk
pdx
peru
philippines
phoenix
pinoy
pocketgitclient
polish
popkorn
portugal
practical-functional-programming
proguard
prozis-android-backup
pyhsikal
python
python-contributors
quasar
random
re
react
reaktive
realm
realworldkotlin
reductor
reduks
redux
redux-kotlin
refactoring-to-kotlin
reflect
refreshversions
reports
result
rethink
revolver
rhein-main
rocksdb
romania
room
rpi-pico
rsocket
russian
russian_feed
russian-kotlinasfirst
rx
rxjava
san-diego
science
scotland
scrcast
scrimage
script
scripting
seattle
serialization
server
sg-user-group
singapore
skia-wasm-interop-temp
skrape-it
slovak
snake
sofl-user-group
southafrica
spacemacs
spain
spanish
speaking
spek
spin
splitties
spotify-mobius
spring
spring-security
squarelibraries
stackoverflow
stacks
stayhungrystayfoolish
stdlib
stlouis
strife-discord-lib
strikt
students
stuttgart
sudan
swagger-gradle-codegen
swarm
sweden
swing
swiss-user-group
switzerland
talking-kotlin
tallinn
tampa
teamcity
tegal
tempe
tensorflow
terminal
test
testing
testtestest
texas
tgbotapi
thailand
tornadofx
touchlab-tools
training
tricity-kotlin-user-group
trójmiasto
truth
tunisia
turkey
turkiye
twitter-feed
uae
udacityindia
uk
ukrainian
uniflow
unkonf
uruguay
utah
uuid
vancouver
vankotlin
vertx
videos
vienna
vietnam
vim
vkug
vuejs
web-mpp
webassembly
webrtc
wimix_sentry
wwdc
zircon
Powered by
Title
l

Leon K

02/23/2020, 1:01 PM
Could anyone talk about the current state of the two "type-class"-like KEEP-proposals? (https://github.com/Kotlin/KEEP/pull/176 and https://github.com/Kotlin/KEEP/pull/87) What is their current status? Is there any indication that one of them will be implemented into the language in the "not-so-distant" future?
r

raulraja

02/23/2020, 5:48 PM
Regarding type classes as far as KEEP-87 is concerned is being reworked in a much more flexible system that allows encoding of type classes, type refinements, union types etc. We are working on it on Arrow Meta and it's called Type Proofs. We plan on resubmitting keeps for all these features after April as we test them in the arrow code base.
❤️ 1
It's currently still on meta on a branch but soon will make it to master and when it does anyone can try them out
Type classes and polymorphism as designed in meta works for both subtype and ad-hoc polymorphism. It eatablishes synthetic subtype relationships between the types and replaces impossible casts for proofs.
l

Leon K

02/23/2020, 5:51 PM
union types as in
fun foo(x: String | Int) = when(x) {
  is String -> {...}
  is Int ->  {...}
}
? that sound's awesome!
r

raulraja

02/23/2020, 5:52 PM
Type classes as in proyecting members from one type to another as syntax https://github.com/arrow-kt/arrow-meta/blob/sv-test-proofs/prelude/src/main/kotlin/arrow/typeclasses.kt
Yeah unions like those
l

Leon K

02/23/2020, 6:00 PM
that looks incredibly promising! You guys are doing god's work over at arrow! could you explain the
Syntax<A>
part? what does that
Syntax
interface do / mean?
:arrow: 1
1
r

raulraja

02/23/2020, 6:01 PM
It may auto generated but essentially type classes have two kinds of members
Static constructors and member functions
To work naturally with Kotlin subtyping it's best to differentiate them so you can project them over the companion or over the data type accordingly
The proof establishes a subtype relationship
When a type cast occurs then it replaces it for the function
It's propositions between types via a morphism/function
The Curry Howard Lambek correspondence with some limitations and other ways to implement things where you would use path dependent types
We plan on hooking then to a theorem prover solver to do something similar to what Scala stainless does and have stronger constrains.
At that point proofs will be able to verify formally local programs that are a pure subset of Kotlin and that we model for the solver
ADTs, equality, vals, etc
We were hoping to use Arend from Jetbrains but it seems it's not yet at that point so most likely will end up depending on inox ir similar to hook to the constrain solver
We will submit keeps for most or many of these features in case they are interesting to the lang in 2020
l

Leon K

02/23/2020, 6:12 PM
I'll need to wrap my head around most of that, haha! sounds brilliant! How much of that can you imagine ever being implemented into standard kotlin? I feel like It's realistic to have Unions some day, and the whole KEEP-87 idea seems to be pretty universally liked as well, but I cannot really imagine having anything resembling dependent types or type-based Proofs in Kotlin.. but maybe that's just me ;D
r

raulraja

02/23/2020, 6:16 PM
I'm not sure but the good news is that plugins are already powerful enough to do these things and the output they produce is compatible in regular Kotlin
As a user nothing stops me from adopting these features in the same way I use the serialization plugin or the allopen plugin, or jetpack compose which entirely relies on plugins
The biggest showstopper at the moment is that IDEA doesn't autoload IDE plugins projects depend on
And for some of these features you'd like proper IDE support
BTW we have type refinements without path dependent types
Predicates are standard Kotlin
l

Leon K

02/23/2020, 6:27 PM
so the compiler check's the String-literal in
TwitterHandle("@adminxxxxxxxxxxxxxxxxxxxxxxxx")
, check's it with the validate function and then knows it's not a valid TwitterHandle, thus the code does not compile? That sounds pretty cool! But how does this work with non-literal values? I see you have these examples:
val runtimeAdminWillBeNull: TwitterHandle? = admin 
//null

val runtimeWhateverIsValidated: TwitterHandle? = whatever 
//TwitterHandle("@whatever")
.. Am I correct in understanding it the following way: if you provide a literal, the compiler can know that your value is either valid or not, and validate the type at compile-time. If you give it a value or otherwise a "calculation", It cannot compile-time verify and thus returns a nullable type?
👍 1
r

raulraja

02/23/2020, 6:34 PM
Yes, thou it can be the full validation map,.either or other type beside nullable
Whatever you add a proof for. There is a nullable type.
A proof is nothing but a global extension function between two types that the type system trusts
l

Leon K

02/23/2020, 6:39 PM
So this is a kind of implicit conversion, specialized for type-refinement? you provide the
@Proof
function that converts from
String -> TwitterHandle?
(or one that converts into
Maybe<TwitterHandle>
, etc) which is then used to generate the inline class instance? what would happen if i did
TwitterHandle(admin)
(put a non-literal value into the constructor)?
r

raulraja

02/23/2020, 6:56 PM
It fails to compile and forces you to use instead
TwitterHandle.from
or one of the validation methods in the refined interface, still under design
l

Leon K

02/23/2020, 7:04 PM
that makes sense, i guess ;D I'll look be looking forward to try that stuff out! Thanks for your time, man ;D
r

raulraja

02/23/2020, 7:07 PM
No problem, any time! 🙂