Should match cases use a keyword instead of pipe?

[andymcn]

Currently each case in a match is indicated with a pipe symbol, eg:

match _first
| None => _first = ex'
| as ex: Exchange =>
  _first = None
end

It has been suggested that starting lines with a pipe makes it look like the continuation of an expresison on the previous line, especially to those of us used to C. Using a keyword instead may reduce this problem.

match _first
case None => _first = ex' // store this, wait for another submission
case as ex: Exchange =>
  _first = None // reset the stored submission to None
end

[andymcn]

Another option would be to indent the cases:

match _first
  | None => _first = ex'
  | as ex: Exchange =>
    _first = None
end

This makes things clearer to me, but then has the problem that it looks like there's an end mssing after the last case.

[sylvanc]

I prefer the pipe symbol, possibly because it's familiar from OCaml, etc. The only concrete reason I have for preferring it is for cases like this:

match x % 100
| 11 | 12 | 13 => "th"
else
  match x % 10
  | 1 => "st"
  | 2 => "nd"
  | 3 => "rd"
  else
    "th"
  end
end

Note the combination of the initial 11, 12 and 13 cases.

[andymcn]

Let's try the same example with a keyword, I'm using case because I'm lazy.

One case per line option:

match x % 100
case 11
case 12
case 13 => "th"
else
  match x % 10
  case 1 => "st"
  case 2 => "nd"
  case 3 => "rd"
  else
    "th"
  end
end

And the same with case indentation:

match x % 100
  case 11
  case 12
  case 13 => "th"
else
  match x % 10
    case 1 => "st"
    case 2 => "nd"
    case 3 => "rd"
  else
    "th"
  end
end

Cases grouped on a line option:

match x % 100
case 11 case 12 case 13 => "th"
else
  match x % 10
  case 1 => "st"
  case 2 => "nd"
  case 3 => "rd"
  else
    "th"
  end
end

And the same with case indentation:

match x % 100
  case 11 case 12 case 13 => "th"
else
  match x % 10
    case 1 => "st"
    case 2 => "nd"
    case 3 => "rd"
  else
    "th"
  end
end

I think that works well either on separate lines or grouped on a line, but it's definitely better with cases indented

[sophiaIC]

I agree with Andy that indentation is good. After all, you also use indentation for the two branches of an if-statement.

[sylvanc]

We've decided to keep the pipe and not replace it with a keyword.