Re: Next Version of Lua

[Patrick Donnelly <batrick@...>]

Hi David,

On Thu, Jun 11, 2009 at 8:58 PM, David Manura<dm.lua@math2.org> wrote:
> On Thu, Jun 11, 2009 at 12:45 PM, Michael Newberry wrote:
>> it would be nice to have more detailed compiler messages.
>> For example, considering assignment instead of a test:
>>
>>   a = 1
>>   if a = 1 then foo end
>>
>> gives
>>   Error: Loading Module 'Script Document1': :2: `then' expected near `='
>
> The error does make sense in a way.  "a" forms a complete expression.
> "if <exp>" should be followed by "then".
>
> But you are correct in that the problem almost certainly lies with an
> incorrect expression rather than the "then".  Here's a patch:
>
> --- lua-5.1.4/src/lparser.c
> +++ lua-5.1.4-better-errors/src/lparser.c
> @@ -1132,6 +1132,8 @@
>   int condexit;
>   luaX_next(ls);  /* skip IF or ELSEIF */
>   condexit = cond(ls);
> +  if (ls->t.token == '=')
> +    error_expected(ls, TK_EQ);
>   checknext(ls, TK_THEN);
>   block(ls);  /* `then' part */
>   return condexit;
>
> Example:
>
>  if a = 1 then print() end
>  --> stdin:1: '==' expected near '='

I don't agree with this because it implies that Lua only expects the
'==' token after 'a'. I think that could be more confusing.

-- 
-Patrick Donnelly

"Let all men know thee, but no man know thee thoroughly: Men freely
ford that see the shallows."

- Benjamin Franklin