Re: Why is "then" required in the if statement?

[Rici Lake <lua@...>]

On 1-Dec-07, at 4:11 PM, Fabien wrote:

> You can get rid of the "then" without adding ambiguity for the 
> compiler. Ditto for the "do" in "while/do/end" and "for/do/end". There 
> is a patch somewhere allowing this.

Yes but it is not always unambiguous. Consider:

  if x or y (x or y)() end

The only way to write that without 'then' would be to use a semicolon, 
but that's
currently ungrammatical (there are no empty statements in Lua) and in 
any event not
particularly readable.

The case of making 'do' optional is even worse. Consider:

local result = {}
for k, v in pairs(t) -- do --
  do local x = make_a_huge_object(v)
     result[#result + 1] = summary(x)
  end
  do_a_long_computation(k)
end

The first do (the one commented out) must be either required or 
prohibited. If it
is optional, the above loop cannot be parsed correctly with a limited 
lookahead parser.
If it is prohibited, you'll end up with the same ambiguity as in the if 
statement above.

> But if you want to save a couple of keystrokes, don't suppress 
> keyword; pick a proper editor and customize its macros. The main 
> interest of a well designed syntax is to improve code readability, and 
> thus maintainability. It's always at least partially a matter of 
> taste, but I'd guess most people would find "if foo then bar end" more 
> readable than "if foo bar end". I definitely would, at least.

Me too. You might even just customize your editor's tab-completion, if 
it has such a feature.