Re: Adding a Return() function

["Thierry@spoludo" <thierry@...>]

Well, we have assert and we have error and no macro nor typing constraints . Error has a ‎parameter for the level of error, but it rather means depth in the callstack. 
‎Assert returns the evaluation and is fatal.
Maybe there is room for generalization ‎at the language level? 

So I will Just muse on not deeply thought concepts.

<- condition [, message [, level ]] -> ‎ non fatal, optional (by interpreter command line argument) , ie error like, but returns the condition evaluation like assert or exit the function with nil, message

‎<+ condition [, message [, level ]] +> same as above but always checked 
‎
‎<* condition [, message [, level ]] *>  same as assert but with a level parameter.

Why not ‎keep the function call or use a keyword ? Mainly because of willing to cover type contraints but introducing keywords may be better. 
‎
function ‎divide(
  a, 
  b <+ b ! = 0 and b +>, -- implicit assign in grammar context,
 fn <- type(fn) == "string" and fn -> -- can we check both constraint always and return cumulated messages ? Can we avoid "and fn"?
) 
‎ local f = <* ‎io.open(fn, "w"), "can't write in "..fn *> -- keep assert keyword as an alias?
 return a/b
end
‎
  Original Message  
From: Javier Guerra Giraldez
Sent: mercredi 17 décembre 2014 10:03
To: Lua mailing list
Reply To: Lua mailing list
Subject: Re: Adding a Return() function

On Wed, Dec 17, 2014 at 2:25 AM, Hao Wu <wuhao.wise@gmail.com> wrote:
> I think OP's point is return can be a function so it can be baked into the
> expression v.s. a single statement, for simplicity.


yes, i was just pointing a third option that is shorter, more readable
(IMHO) and currently valid.

when any function has some 'fail fast' condition(s), i like to add one
or more such 'guard lines' as close to the top as possible. also, if
the "then" clause ends with a return, i don't put an "else" for the
rest of the function, avoiding useless indentation and too many 'ends'
at the end.

function division(x,y)
if y==0 then return nil, "division by zero" end
return x / y
end

instead of:

function division(x,y)
if y==0 then
return nil, "division by zero"
else
return x/y
end
end

the OP proposal would be:

function division(x,y)
if y!=0 or Return(nil, "division by zero") then
return x/y
end
end

which i think is much less readable than either of the others, and not
shorter than the first one.

-- 
Javier