Consider making `;` a statement separator instead of expression list separator

[leafo]

Current Behavior

Currently, ; is only valid as an alternative to , in a few specific contexts (ExpListLow):

• Return statements: return a; b
• Assignments: x = a; b
• Exports: export x = a; b

This was introduced in 2011 as a "value separator" to help disambiguate from function calls, but it's an obscure feature that few users likely know about or use.

Proposal

Remove the current ; behavior and repurpose it as a statement separator, allowing multiple statements on a single line while preserving the current indentation level. This would align with Lua's syntax.

Examples

-- Simple one-liners
x = 1; y = 2

-- Short related statements
i += 1; j += 1

In block contexts

The semicolon would maintain the current indentation:

if condition
  setup!; run!; cleanup!

Equivalent to:

if condition
  setup!
  run!
  cleanup!

Breaking Changes

This removes the ability to use ; as a value separator in return/assignment/export. Users would need to switch to ,:

-- No longer valid
return a; b

-- Use instead
return a, b

This usage is likely rare since , works identically and is more conventional.

[pigpigyyy]

I’ve been using MoonScript for a long time, and I have never actually used the ;-based value separation feature, even though I know it exists.

In practice, I find this old syntax:

return f1 1,2; 3

to be non-obvious and visually misleading. At a glance, it looks very close to a normal statement separator, but it secretly encodes return semantics and value grouping. That makes it hard to read and easy to misunderstand, especially for people coming from Lua or other languages.

I’d also suggest tightening the semantics in two specific ways to avoid subtle reading errors:

1. Disallow using f 1, 2; 3 as the final line of a block to implicitly return 3.
   When this appears at the end of a function or block, it could misread as one statement, while it actually returns the second value. Forbidding this form would eliminate a class of visually ambiguous implicit returns.

2. If a statement ends with ;, it should cancel implicit return.
   In other words, when something like:

   f 1, 2;
   

   appears as the last line of a block, it should not participate in implicit return at all. The semicolon should clearly signal “statement termination, value discarded”.