Grammar Ambiguity in while

[iwillspeak]

Given the following:

var foo: Bool = true

while foo
	  (print 100)
end

The parse tree will be a function call to foo, rather than a grouping expression in the body of the while loop. To solve this we need some kind of expression separator.

• For while we could mandate () around the condition
• For while we could have an opening do or similar
• For all expressions we could use end of line as a separator. Expressions would only parse infix operators over newlines if they're in a grouping expression?
• Some kind of explicit statement separator to fix this in the general case, e.g. ; in C

In general I'm not a fan of the whitespace solution. I'd rather the language wasn't whitespace sensitive. If we move to a traditional if/elif/else block this will become more pressing as the same ambiguity exists there.

[iwillspeak]

The Ruby grammar appears to solve this problem with a pair grammar non-terminals:

• T, which can be either ;, or \n
• DO, which is either the literal "do" or T.

which means you can write loops like while foo do (100) end and

while foo
   (100)
end