Re: Noob question -- On error, exit function and terminate script

[Lorenzo Donati <lorenzodonatibz@...>]

On 25/06/2011 18.18, Xavier Wang wrote:

[snip]

> Sorry, but I mean, a new version of assert against the baselib one that
> _don't_ evaluate the second expression if the first expression is true.

I don't think this is possible without altering deeply the semantics of 
the language, since "assert" is a regular function (although implemented 
in C), so all its arguments are evaluated before the call.

The possible solutions I see both involve change in the language:

1. turn "assert" into some sort of operator, which its kind of short 
circuit evaluation (like "and" and "or").

2. introduce a way of telling Lua to delay the evaluation of an 
expression (this has been proposed before IIRC).

I wouldn't want the first (too specific). Maybe the second could have 
its applications if done well and it may be general enough to fit Lua's 
spirit.

P.S.: note that you can achieve sort of "short circuited" assert writing:

local _ = condition or error( msg )

instead of

assert( condition, msg )

But I don't like that idiom too much. It doesn't save too much typing 
compared to:

if not condition then error( msg ) end

and it is less explicit (i.e. unreadable ).


-- Lorenzo