scala/scala

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Fabio Labella

@SystemFw

try taking two Model[_] and assigning the values of type State inside them to each other

and you'll see a weird error about _1and _2

this is how a lot of people come across existentials for the first time

it makes their code magically compile at first (since it accepts anything)

Vinayak Pathak

@vinayakpathak

i see... coz it will think the first model's State is different from the second one's State?

Fabio Labella

@SystemFw

and then it fails later

Vinayak Pathak

@vinayakpathak

yes that's sort of what happened with me :)

Fabio Labella

@SystemFw

coz it will think the first model's State is different from the second one's State

more precisely, it will think that it has no way to know, which is what existential quantification is all about

Vinayak Pathak

@vinayakpathak

yes ok got it

Fabio Labella

@SystemFw

even if you pass two Model which do have the same State, you have hidden that information

when you add refinements and Aux to an abstract type, you are propagating that info again

Vinayak Pathak

@vinayakpathak

right

ok this makes a lot more sense... thanks for spending all this time explaining this!

Rob Norris

@tpolecat

:clap:

Fabio Labella

@SystemFw

@vinayakpathak no problem :)
There's a whole field or two of computer science about this stuff, so don't worry if you find it tricky

Vinayak Pathak

@vinayakpathak

type theory being one of them i guess?

is there a type theory book you'd recommend btw?

Rob Norris

@tpolecat

Path-dependent [existential] types are one of the defining features of Scala but they're poorly understood. Even by scalac in some cases. Poorly explained also.

Fabio Labella

@SystemFw

well, Types and Programming Languages is kinda the standard

also note that scala is somewhat unique in this regard

some things are novel, others require some skill to be linked to the theory

Vinayak Pathak

@vinayakpathak

i see i see... i will checkout that book

Rob Norris

@tpolecat

This series on the typelevel blog is pretty good, re: this specific issue in Scala https://typelevel.org/blog/2015/07/13/type-members-parameters.html

Fabio Labella

@SystemFw

this is one aspect where theoretical background does help

Vinayak Pathak

@vinayakpathak

i have spent a lot of time on the other side of computer science theory, i.e., algorithms and complexity... only recently discovered the type theory, category theory etc... and it's all super fascinating

Fabio Labella

@SystemFw

otherwise it's hard to make intuition precise

@vinayakpathak I'd also recommend some basic study of logic

nothing too advanced, but the basics do help when reading about type theory

on the other side of computer science theory,

there's more... it's a fractal rabbit hole

one random example: models of computation, applied to concurrent and distributed computation

Vinayak Pathak

@vinayakpathak

i agree :)

Fabio Labella

@SystemFw

I wish people appreciated it more

Vinayak Pathak

@vinayakpathak

i feel that broadly though cs theory can be divided into the Turing style areas and the Church style areas

Turing style being algorithms, running time, complexity, etc... Church style being more logic, type theory, that sort of stuff

not sure what kinds of models of concurrent and distributed computations you are talking about... i remember seeing some in my grad school days, but they were mostly Turing style

@tpolecat thanks will check it out

Fabio Labella

@SystemFw

I mean, I don't want to open a whole new rabbit hole to dive into, type theory is big enough. But things like pi calculus, join calculus, model and temporal logic, and so on

Vinayak Pathak

@vinayakpathak

I don't want to open a whole new rabbit hole to dive into

yeah makes sense :)

elyphas

@elyphas

Hi, someone could tell me, why this give a true result?

def isNumber(s: String): Boolean = s.matches("[+-]?\\d+.?\\d+")

println(isNumber("1"))

Marcell

@yohannesm

anyone familiar with sbt? I am trying to figure out if I can access a file hosted not on my local machine but like somewhere on S3 instead? Trying to host our scalafmt conf to be working with Jenkins and our build process

elyphas

@elyphas

well seems that this solved my problem:

s matches """\d+"""

Marcell

@yohannesm

scalafmtConfig in ThisBuild := file("~/.scalafmt.conf") <- Something like that but instead of a local file it could pull it off http somewhere?

monksy

@monksy

With scala is there a huge drive to move all methods to functions (in objects)?

Marcell

@yohannesm

not really

functional programming is just we want to make sure functions are "pure" as in without side effects

side effects should be encapsulated in some sort of Monads

at least that's what I understand

monksy

@monksy

methods create side effects

Marcell

@yohannesm

as long as the methods is not mutative, it should be not creating side effects

Long Cao

@longcao

methods don't always create side effects, but often times you do see methods side effecting in say, very OOP code like in Java, e.g. myInstance.setSomething(something)

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