indentation-syntax.md

Scala indentation syntax

An interesting choice, probably too late. Right now Scala should focus on reducing paper cuts and puzzlers. This said; if indentation syntax is comming, I want it to be an improvement rather than

What is proposed

extend optionality of braces

we already do it! This is already legal for single-line method definitions

def add(l: Int, r: Int): Int = l + r

// or even
def add(l: Int, r: Int): Int =
  l + r
  

It's also legal for match-case blocks.

The problem

Why not the colon?

• already overloaded

scala/scala3#7136

The Case For The Equal Sign

Simple assignment, equal sign + brace

val foo = { 1 }

Simple assignment, dropping brace

val foo = 1

def fib(n) = {
    if (n == 0) then 0
    else if (n == 1) then 1
    else fib(n-1) + fib(n-2)
}

def fib(n) = 
    if (n == 0) then 0
    else if (n == 1) then 1
    else fib(n-1) + fib(n-2)

class Rational:
    def __init__(self, x, y):
        self.numerator = x
        self.denominator = y

class Rational(x: Int, y: Int) = {
    val numerator = x
    val denominator = y
}

class Rational(x: Int, y: Int) =
    val numerator = x
    val denominator = y

def fib(n):
    if n == 0: return 0
    elif n == 1: return 1
    else: return fib(n-1) + fib(n-2)

the proposed role of = in indentation syntax

regularize syntax

Python syntax is easy because it is regular. Creating

def name(ref):
    body1
    body2

class name(ref):
    body1
    body2
    

The proposed Scala 3 indentation syntax isn't.

object Foo extends Qux:
    body1
    body2
    
class Foo(param: Ref):
    body1
    body2
    
def qux(param: Ref): Foo =
    body1
    body2

Defining methods stands out like a sore thumb.

How to regularize Scala 3 indentation syntax

Let's buy into =. It's already in use and is not overloaded with meaning.

def foo(param: Ref): Foo =
    body1
    body2
    body3

This looks just what we had in the colon-indentation-syntax.

object Bar extends Qux = 
    body
    body
    
class Foo2(param: Ref) =
    body
    body