Scala

« first day (473 days earlier) ← previous day next day → last day (805 days later) »

6:09 PM

This isn't a tutorial, just a brief primer for Python programmers: docs.scala-lang.org/scala3/book/scala-for-python-devs.html

DLosc

It's true that the Scala book does start off with a bunch of "Scala's type system has this great feature," which doesn't mean anything if you don't know a lot about type system theory (I don't). It might be best to start from this point instead.

user

lmao yeah

DLosc

Scastie is really helpful for trying out small snippets. You don't have to figure out the boilerplate and compile process for a full program.

user

If you don't have Scala installed but you do have sbt, try sbt console to get the REPL

mathcat

I think I know a bit about the console

but how does a .scala file work?

does it have a main class or smth like that?

user

6:13 PM

It only needs a main class if you're going to run that file

In Python, you'd check if the filename is main inside that. In Scala, you'd have @main def helloWorld = println("Hello World!") or an object with a main method

Only one Scala file in your entire project needs a main class (in Python too you don't run every single module as the main module)

mathcat

nice thanks

mathcat

6:36 PM

@main def HelloWorld = {
  var i = 2+2
  println(i)
}

^ What's the problem?

user

Are you trying to run this in Scastie?

What error are you getting?

That looks like a valid program (could be improved but that isn't important right now)

mathcat

@user I'm running it is Main.scala

and with scalac in the terminal

Error is error: expected start of definition

user

Which version of Scala did you download? This won't work with Scala 2

If you installed Scala 2, you'd need object HelloWorld { def main(args: Array[String]) = { println(4) } }

mathcat

okay

so sbt version is 3

but scalac version is 2

user

People don't actually use scalac/scala directly in practice, they mostly just use sbt

mathcat

6:45 PM

so using the console?

user

For the REPL, you can try running scala and type in var i = 2+2; i there

mathcat

Can I run the file using sbt?

user

I think you can?

mathcat

or is the only option the REPL?

user

Try Scastie for simple stuff tho

@mathcat The REPL won't let you run the file, just evaluate expressions one by one

mathcat

6:46 PM

okay

user

I'd recommend uninstalling Scala 2 and installing Scala 3 instead if you want to run single file Scala 3 programs

Sorry, if you want to run a single file written in Scala 3, you don't have much recourse

mathcat

I actually have a whole directory

with src, prject and stuff

user

Oh cool

Did you create it with sbt?

mathcat

I think so

user

Oh ok, then you just need to do sbt run or something

Or maybe sbt runMain HelloWorld if that doesn't work?

Here are instructions on a Hello World in sbt

mathcat

6:50 PM

Working!

thanks

I'll try Fizz Buzz

user

np, happy to see it's working

DLosc

7:02 PM

\o/

mathcat

Why is this not working?

nvm

I got it

user

Did you mean to do s +=?

mathcat

yeah

user

s+"Fizz" is just an expression

mathcat

I am confused

user

7:11 PM

About s+?

mathcat

I was confused

anywhat

user

(btw I'd do something like this)

mathcat

I did FizzBuzz!

for (r <- 1 to 100) {
  var s = ""
  if (r % 3 == 0) s+="Fizz"
  if (r % 5 == 0) s+="Buzz"
  if (s.length == 0) s += r
  println(s)
}

user

Yay!

println(
  if (r % 15 == 0) "FizzBuzz"
  else if (r % 5 == 0) "Buzz"
  else if (r % 3 == 0) "Fizz"
  else s"$r"
)

I'd do something like ^ to avoid the mutation of s and the length check

mathcat

mutation?

user

7:14 PM

Changing the value of s (s += foo does s = s + foo)

mathcat

You're not allowed to do that?

user

Oh no you are

It's just not preferred

mathcat

o/ I have to learn

user

You can stick with the mutation, but I'd still suggest making the last check if (s % 3 != 0 && s % 5 != 0)

4 hours later…

DLosc

10:57 PM

@user Why are both _s evaluating to the first argument in 0.to(_).sum/2+_? ATO I'm sure I've seen some anonymous functions with two arguments that use _ for both of them.

user

Hrm

I don't see what's wrong there

The second _ does evaluate to the second argument

(a, b) => 0.to(a).sum/2+b gives the same results

DLosc

Now I'm really confused

user

It makes complete sense to me lol

0.to(4).sum is 10, /2 is 5, +9 is 14

Did you want /(2+9) instead?

DLosc