Luiz Henrique de Figueiredo a écrit :
is there a compelling reason for such limitation?
Size and complexity. If you want to do complex pattern
matching with full RE,
then you can add it as an external libraries (and there
are a few for Lua).
Well, (ab)* isn't so complex, both to implement (I
think) or conceptually (that's not (?<=\w{5})...).
And as I wrote, we often find Lua embedded in softwares
(SciTE...) which use only base libraries and don't plan
to offer extra advanced features, so we are stuck.
Now, I take this as a "No, thanks". :-(
I found myself wishing to have a continue keyword [...]
can't recall an official reason why it isn't in the
language.
Lua evolves by answering "why?" not "why not?".
Well, I wrote it: I can do without, but by adding extra
levels of 'if' nesting and indenting, which can be ugly
with a complex automaton.
In such algorithm, I often has to test a state and / or
condition, and if meet, do something and continue with
the next iteration (ie. do nothing else for this step),
else check the next state and / or condition.
for line in fileHandle:lines() do
if IsState(a) then
-- Do stuff
elseif IsState(b) then
-- Do stuff too
elseif IsState(c) then
s, e = string.find(line, ...)
if s ~= nil then
-- Do it
else
s, e = string.find(line, ...)
if s ~= nil then
-- Process that
else
-- Etc.
end
elseif IsState(d) then
-- Stuff doing
end
end
for line in fileHandle:lines() do
if IsState(a) then
-- Do stuff
elseif IsState(b) then
-- Do stuff too
elseif IsState(c) then
s, e = string.find(line, ...)
if s ~= nil then
-- Do it
continue -- No further test needed
end
s, e = string.find(line, ...)
if s ~= nil then
-- Process that
continue -- Idem
end
-- Etc.
elseif IsState(d) then
-- Stuff doing
end
end
The given example isn't compelling, but with complex
automatons, it can go far.
Now, the code can probably be refactored, I haven't
searched much this way.
Oh well, I suppose convenience features beyond simple
syntactic sugar are beyond question.
Oh, while I am on the topic, I found some surprising
results with string.find.
I found that if string.find returns nil, all
sub-captures are nil.
Otherwise, they don't match something, they are just
empty.
Well, that's logical (they just matched empty string).
Not a problem but I wanted to mention it.
Also if the whole pattern matches the empty string (eg.
with %w*),
the end index is the start index (equal to 'init') less
one.
This is not documented.
--
Philippe Lhoste
-- (near) Paris -- France
-- http://Phi.Lho.free.fr
-- -- -- -- -- -- -- -- -- -- -- -- -- --
