Extend infix operators with instructions for the formatter.

[cristianoc]

This extends infix operators #6076 with instructions for the formatter.
The @@infix.add instruction tells the formatter to transform existing code, into code using infix operators.
The @@infix.remove instruction does the opposite: tells formatter to transform code written using infix operators, into code that does not use them.

Example of add:

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.add(("😀", "plus"))
@@infix.add(("💩💩", "minus"))

let q = minus(plus(3, 4), 5)

reformats to

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix(("😀", "plus"))
@@infix(("💩💩", "minus"))

let q = 3 😀 4 💩💩 5

Example of .remove:

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.remove(("😀", "plus"))
@@infix.remove(("💩💩", "minus"))

let q = 3 😀 4 💩💩 5

reformats to

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.remove(("😀", "plus"))
@@infix.remove(("💩💩", "minus"))

let q = minus(plus(3, 4), 5)

[fhammerschmidt]

Looks great!

I would rather have a @@infix.reset (or similar) annotation to just disable all infixes again, though.

Also, are there any forbidden characters or a length restriction?

[glennsl]

What would be the result in this case:

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.add(("😀", "plus"))
@@infix.add(("😀", "minus"))
@@infix.remove(("😀", "minus"))

let q = 3 😀 4

or

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.add(("😀", "plus"))
@@infix.add(("😀", "minus"))
@@infix.remove(("😀", "plus"))

let q = 3 😀 4

And would it be possible to use normal scoping rules instead of explicit remove declarations, e.g.:

let plus = (x, y) => x + y
let minus = (x, y) => x - y

%%infix(("😀", "plus"))

let x = {
  %%infix(("😀", "minus"))
  3 😀 4  // 3 - 4
}

let q = 3 😀 4 // 3 + 4

This feels much more natural to me in a functional language.

[cristianoc]

Looks great!

I would rather have a @@infix.reset (or similar) annotation to just disable all infixes again, though.

Also, are there any forbidden characters or a length restriction?

That's not what .remove does: it actively converts things back (on reformat), as opposed to just ignoring @@infix added earlier.

Btw the .xxx variants, which are purely instructions for the formatter, are kind of nice to play with, to know that it's possible to automatically convert existing code into- and out-of infix, but are not really an essential part.

[cristianoc]

Also, are there any forbidden characters or a length restriction?

Not right now, as an initial exploration. But one could be more prescriptive.

[cristianoc]

What would be the result in this case:

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.add(("😀", "plus"))
@@infix.add(("😀", "minus"))
@@infix.remove(("😀", "minus"))

let q = 3 😀 4

or

let plus = (x, y) => x + y
let minus = (x, y) => x - y

@@infix.add(("😀", "plus"))
@@infix.add(("😀", "minus"))
@@infix.remove(("😀", "plus"))

let q = 3 😀 4

And would it be possible to use normal scoping rules instead of explicit remove declarations, e.g.:

let plus = (x, y) => x + y
let minus = (x, y) => x - y

%%infix(("😀", "plus"))

let x = {
  %%infix(("😀", "minus"))
  3 😀 4  // 3 - 4
}

let q = 3 😀 4 // 3 + 4

This feels much more natural to me in a functional language.

The result is pretty much undefined (whatever the quick implementation happens to be doing right now).

Adding scope makes sense. There's a state mechanism this inserts into, and that mechanism currently does not preserve scoping. That's pretty random and not intended, but wanted to check that there are no consequences to the existing mechanism first.

[cristianoc]

So yes scoping makes sense. And .remove really is a different thing than closing a scope: it's an instruction for the formatter, to be executed once, rather than something that stays in the final code.

So perhaps I should remove .add and .remove from the description, as they mostly only cause confusion.

[cristianoc]

Added per-module scope.

[cristianoc]

Moving to a more basic PR without .add and .remove: #6076