few questions

[Aleksey Perfilov]

Hi, guys.

 

I need help with improving my syntax error messages.

 

Right now I just have standard bison error handling where it looks at possible tokens and

 

says <token> expected.

 

Few quetions, if you don't have time to read all, please answer just on one or two of them.

 

question 1:

 

I am not exactly clear on contents of yytable, what does it mean "portions for different

 

uses" ? What do those portions contain and in what format?
for example if I have

 

yyn=yypact[ystate]
yyn+=YTERROR
yyn=yytable[yyn]

 

what do last two expressions mean?

 

question 2:

 

if I put an error token in a rule that doesn't have a closing token like this

 

stmnts:  /* empty string */
        | stmnts '\n'
        | stmnts exp '\n'
        | error

 

is error token going to match all of the remaining output if syntax error occurs?

 

question 2:

 

what if I have a mid rule where I decide that something's wrong and want to ignore the whole

 

_expression_

 

expr : part1 { some checks here } part2 part3 part4 part5

 

How can I go about it?

 

question 3:

 

If I get an error in lexer, for example closing comment w/o opening comment, how can I get

 

the parser to ignore the token or maybe a serie of tokens?
For example if I have a construct IF outside of a function in C++ I need to ignore the whole

 

thing and continue parsing next function.
Is it just a matter of smart error token usage?

 

question 4:

 

In Bison code there is YYFAIL macro that goes to yyerrlab:
Is it the default action when an error is encountered?

 

question 5:

 

For example if I have a piece of program like this:

 

a=1
b=2;

 

when parser reads "b" it errors, I print "missing semicolon" but then I want to continue

 

parsing. How do I put back "b" so that b=2; is parsed successfully.

 

thanks in advance