Is it possible to parse Block through flex and bison??
Example:
Suppose
BEGIN BLOCK BLK_ROWDEC
NAME cell_rowdec
SIZE UNI_rowdecSize
ITERATE itr_rows
DIRECTION lgDir_rowdec
STRAP STRD1,STRD3,STRD2
WRAP WRD1
VIA VIAB,VIAC,VIAD
ENDS BLK_ROWDEC
Now I want to check Is BEGIN and END is belong to same block or not?/Is it possible with flex and bison
Yes it's possible, just save the block name with the BEGIN and check it when you get the END.
But the block name is redundant here, and Bison will match up begins and ends automatically. If you can remove it from your syntax I would do so.
Related
I'm trying to modify an existing lua script that cleans up subtitle data in Aegisub.
I want to add the ability to delete lines that contain the symbol "♪"
Here is the code I want to modify:
-- delete commented or empty lines
function noemptycom(subs,sel)
progress("Deleting commented/empty lines")
noecom_sel={}
for s=#sel,1,-1 do
line=subs[sel[s]]
if line.comment or line.text=="" then
for z,i in ipairs(noecom_sel) do noecom_sel[z]=i-1 end
subs.delete(sel[s])
else
table.insert(noecom_sel,sel[s])
end
end
return noecom_sel
end
I really have no idea what I'm doing here, but I know a little SQL and LUA apparently uses the IN keyword as well, so I tried modifying the IF line to this
if line.text in (♪) then
Needless to say, it didn't work. Is there a simple way to do this in LUA? I've seen some threads about the string.match() & string.find() functions, but I wouldn't know where to start trying to put that code together. What's the easiest way for someone with zero knowledge of Lua?
in is only used in the generic for loop. Your if line.text in (♪) then is no valid Lua syntax.
Something like
if line.comment or line.text == "" or line.text:find("\u{266A}") then
Should work.
In Lua every string have the string functions as methods attached.
So use gsub() on your string variable in loop like...
('Text with ♪ sign in text'):gsub('(♪)','note')
...thats replace the sign and output is...
Text with note sign in text
...instead of replacing it with 'note' an empty '' deletes it.
gsub() is returning 2 values.
First: The string with or without changes
Second: A number that tells how often the pattern matches
So second return value can be used for conditions or success.
( 0 stands for "pattern not found" )
So lets check above with...
local str,rc=('Text with strange ♪ sign in text'):gsub('(♪)','notation')
if rc~=0 then
print('Replaced ',rc,'times, changed to: ',str)
end
-- output
-- Replaced 1 times, changed to: Text with strange notation sign in text
And finally only detect, no change made...
local str,rc=('Text with strange ♪ sign in text'):gsub('(♪)','%1')
if rc~=0 then
print('Found ',rc,'times, Text is: ',str)
end
-- output is...
-- Found 1 times, Text is: Text with strange ♪ sign in text
The %1 holds what '(♪)' found.
So ♪ is replaced with ♪.
And only rc is used as a condition for further handling.
What would be the best way to capture the inner text in the following case?
inner_text = any*;
tag_cdata = '<![CDATA[' inner_text >cdata_start %cdata_end ']]>';
The problem is, it seems like the cdata_end action fires several times due to the fact that inner_text could match ].
I found the solution. You need to handle non-determinism. It wasn't clear initially, but the correct solution is something like this:
inner_text = any*;
tag_cdata = '<![CDATA[' inner_text >text_begin %text_end ']]>' %cdata_end;
action text_begin {
text_begin_at = p;
}
action text_end {
text_end_at = p;
}
action cdata_end {
delegate.cdata(data.byteslice(text_begin_at, text_end_at-text_begin_at))
}
Essentially, you wait until you are sure you parsed a complete CDATA tag before firing the callback, using information you previously captured.
In addition, I found that some forms of non-determinism in Ragel need to be explicitly handled using priorities. While this seems a bit ugly, it is the only solution in some cases.
When dealing with a pattern such as (a+ >a_begin %a_end | b)* you will find that the events are called for every single a encountered, rather than at the longest sub-sequence. This ambiguity, in some cases, can be solved using the longest match kleene star **. What this does is it prefers to match the existing pattern rather than wrapping around.
What was surprising to me, is that this actually modifies the way events are called, too. As an example, this produces a machine which is unable to buffer more than one character at a time when invoking callbacks:
%%{
machine example;
action a_begin {}
action a_end {}
main := ('a'+ >a_begin %a_end | 'b')*;
}%%
Produces:
You'll notice that it calls a_begin and a_end every time.
In contrast, we can make the inner loop and event handling greedy:
%%{
machine example;
action a_begin {}
action a_end {}
main := ('a'+ >a_begin %a_end | 'b')**;
}%%
which produces:
I have a problem which i suppose must be very common and most of you would have faced it.
I have written a program in lua, say main.lua which on receiving key event should modify the coordinates and display the geometry figure.
This lua code calls reg.c, where it kind of registers.
Now in reg.c i have a function engine which receives the key pressed and passes it to the lua function responsible for key handling.
But by the time key event comes, lua code is done with the registration and exits, thus the call from engine() becomes illegal memory access leading to segmentation fault.
Also i suppose we can't have lua call hanging in reg function, and call engine function from somewhere else.
Then what should be the solution, please guide me through this.
#jacob: here is the prototype of what i am trying to achieve:
function key_handler() //this function will get the latest key pressed from some other function
{
draw.image();
draw.geometry();
...
...
while(1)
{
//draw Points until some condition goes wrong
}
}
Now, once entered into key_handler, while he is busy drawing the points unless and until the failing condition occurs, i am unable to receive key pressed till that time.
I hope this explanation is much simpler and have made my point, and will help others to understand the problem.
I am really sorry, but i am not good at expressing or making others understand.
One more thing, i ahve followed the C syntax to explain, however this is completely implemented in lua
Your code snippet is still largely non-informative (ideally one should be able to just run your code in a stock Lua interpreter and see your problem). If you're describing a Lua problem, use Lua code to describe it.
However I'm beginning to see where you want to go.
The thing you need to could do is have a coroutine that's called in your key handler, which passes an argument back to your handler:
function isContinue() --just to simulate whatever function you use getting keypresses.
-- in whatever framework you're using there will probably be a function key_pressed or the like.
print('Initialize checking function')
while true do
print('Continue looping?')
local ans = io.read():match('[yY]')
local action
if not ans then
print('Do what instead?')
action = io.read()
if action:match('kill') then -- abort keychecker.
break
end
end
coroutine.yield(ans,action)
end
print('finalizing isContinue')
return nil,'STOP' -- important to tell key_handler to quit too, else it'll be calling a dead coroutine.
end
function key_handler()
local coro = coroutine.create(isContinue)
local stat,cont,action
while true do
print'Draw point'
stat,cont,action = coroutine.resume(coro)
if not stat then
print('Coroutine errored:',cont)
elseif not cont then
print('isContinue interrupted keyhandler')
print("We'll "..action.." instead.")
break
end
end
print('finalizing key_handler')
end
key_handler()
-- type something containing y or Y to continue, all else aborts.
-- when aborting, you get asked what to do instead of continuing,
--- with "kill" being a special case.
This should be self explanatory. You should probably take a good look at Programming in Lua, chapter 9: Coroutines.
The big difficulty (well, if you're not accustomed to collaborative threading) is that a coroutine should yield itself: it's not the calling function that's in charge of returning control.
Hope this helps you.
I'm writing a program where the user must enter a 'yes' or 'no' value. The following is the code that will be executed when the message {createPatient,PatientName} is received.
{createPatient, PatientName} ->
Pid = spawn(patient,newPatient,[PatientName]),
register(PatientName,Pid),
io:format("*--- New Patient with name - ~w~n", [PatientName]),
Result = io:read("Yes/No> "),
{_,Input} = Result,
if(Input==yes) ->
io:format("OK")
end,
loop(PatientRecords, DoctorPatientLinks, DoctorsOnline, CurrentPatientRequests, WaitingOfflineDoctorRequests);
When executed ,the line "New Patient with name..." is displayed however the line Yes/No is not displayed and the program sort of crashes because if another message is sent, then the execution of that message will not occur. Is there a different way to solve this problem please?
There are a number of points I would like to make here:
The io:read/1 function reads a term, not just a line, so you have to terminate input with a '.' (like in the shell).
io:read/1 returns {ok,Term} or {error,Reason} or eof so you code should check for these values, for example with a case.
As #AlexeyRomanov mentioned, io:get_line/1 might be a better choice for input.
The if expression must handle all cases even the ones in which you don't want to do anything, otherwise you will get an error. This can be combined with the case testing the read value.
You spawn the function patient:newPatient/1 before you ask if the name is a new patient, this seems a little strange. What does the newpatient function do? Is it in anyway also doing io to the user which might be interfering with functions here?
The main problem seems to be work out what is being done where, and when.
This is very artificial problem. In erlang any communication is usually inter-process and exchanging strings wouldn't make any sense - you ask question in context of process A and you would like to post answer in context of process B (shell probably).
Anyways, consider asking question and waiting in receive block in order to get an answer.
When question pops out in shell, call a function which will send the answer to 'asking' process with your answer.
So:
io:format("*--- New Patient with name - ~w~n", [PatientName]),
receive
{answer, yes} -> do_something();
{answer, no} -> do_something()
end
The 'answering' function would look like that:
answer(PatientName, Answer) ->
PatientName ! {answer, Answer}.
And shell action:
$> *--- New Patient with name - User1036032
$> somemodule:answer('User1036032', yes).
It is possible to create some dialog with shell (even unix shell), but to be honest it is used so rare that I do not remember those I/O tricks with read and write. http://trapexit.com/ used to have cookbook with this stuff.
Use io:get_line("Yes/No> ") instead.
I am trying to do a syntax text corrector for my compilers' class. The idea is: I have some rules, which are inherent to the language (in my case, Portuguese), like "A valid phrase is SUBJECT VERB ADJECTIVE", as in "Ruby is great".
Ok, so first I have to tokenize the input "Ruby is great". So I have a text file "verbs", with a lot of verbs, one by line. Then I have one text "adjectives", one "pronouns", etc.
I am trying to use Ragel to create a parser, but I don't know how I could do something like:
%%{
machine test;
subject = <open-the-subjects-file-and-accept-each-one-of-them>;
verb = <open-the-verbs-file-and-accept-each-one-of-them>;
adjective = <open-the-adjective-file-and-accept-each-one-of-them>;
main = subject verb adjective # { print "Valid phrase!" } ;
}%%
I looked at ANTLR, Lex/Yacc, Ragel, etc. But couldn't find one that seemed to solve this problem. The only way to do this that I could think of was to preprocess Ragel's input file, so that my program reads the file and writes its contents at the right place. But I don't like this solution either.
Does anyone knows how I could do this? There's no problem if it isn't with Ragel, I just want to solve this problem. I would like to use Ruby or Python, but that's not really necessary either.
Thanks.
If you want to read the files at compile time .. make them be of the format:
subject = \
ruby|\
python|\
c++
then use ragel's 'include' or 'import' statement (I forget which .. must check the manual) to import it.
If you want to check the list of subjects at run time, maybe just make ragel read 3 words, then have an action associated with each word. The action can read the file and lookup if the word is good or not at runtime.
The action reads the text file and compares the word's contents.
%%{
machine test
action startWord {
lastWordStart = p;
}
action checkSubject {
word = input[lastWordStart:p+1]
for possible in open('subjects.txt'):
if possible == word:
fgoto verb
# If we get here do whatever ragel does to go to an error or just raise a python exception
raise Exception("Invalid subject '%s'" % word)
}
action checkVerb { .. exercise for reader .. ;) }
action checkAdjective { .. put adjective checking code here .. }
subject = ws*.(alnum*)>startWord%checkSubject
verb := : ws*.(alnum*)>startWord%checkVerb
adjective := ws*.)alnum*)>startWord%checkAdjective
main := subject;
}%%
With bison I would write the lexer by hand, which lookup the words in the predefined dictionary.