Re: 5.1

[Rici Lake <lua@...>]

On 17-Oct-05, at 5:06 PM, Glenn Maynard wrote:

> I guess this case is impossible to detect at compile-time, though.  
> That
> seems to be a common problem with Lua; I suppose any warning facility
> would need to be runtime.  Yuck.

I'm getting quite used to the run-time "warning"; it looks like this:

foo:27: attempt to call a table value

Now, Lua has no compile-time warning mechanism, and it is not 
particularly clear how one would even add one to the compiler (possibly 
an optional callback function to accept warnings?), but in principle it 
is easy enough to detect most instances of the "missing-pairs" problem 
at compile-time: you simply check for the case in "for <varlist> in 
<exprlist> do" where <exprlist> is a single expression which is not a 
function call of some kind. That's an imperfect check, but it would be 
good enough for a warning.

This is somewhat like the famous C error:

  while (ch = ' ') { ... }

Many C compilers will warn you about that, if asked to, suggesting that 
you write it as:

  while ((ch = ' ')) { ... }

if that's truly what you meant (unlikely, in this case); similarly, you 
could quell the suggested Lua warning (that is, the suggestion I made a 
couple of paragraphs ago) by writing:

  for val in func, nil do

instead of

  for val in func do

if that's what you meant (as opposed to "for val in pairs(func) do")

I'm not sure why Lua deserves any more Yucking than C in this pair of 
vaguely comparable cases, although one would certainly prefer Lua to be 
less Yuckworthy.

R.