[ragel-users] When exactly is the eof variable required?

[Grégory Pakosz]

Hello,

I'm currently discovering Ragel and I am wondering when the eof
variable is required?

More exactly, I noticed in the following in the params.rl example:

output = '-o' 0? string 0 @output;

I understand the machines are defined to accept and consume NUL
characters. This is the reason why the params_execute function is
given strlen(argv[a])+1.

However, if I change params.rl to:

output = '-o' 0? string @output;

Then Ragel starts making use of the eof variable, which params.rl
doesn't define.

Can someone please explain me why removing that 0 in the machine makes
Ragel use the eof variable?

Thank you,
Gregory

[Tim Goddard]

I'm guessing that string can't include the null character, but can be of
variable length (kleene star, etc). When the expression ends with "string",
it could be cut short while still having a valid expression by the end of the
file, and need to take finishing actions when it sees the EOF. When the
expression ends with 0, an EOF could not mark the end of the expression
and cause any other action to be taken, so the eof mark is unused.

The fact that it's a null character will be irrelevant - any character which
can't be in "string" would have the same effect.

Cheers,

Tim

Post by Grégory Pakosz
Hello,
I'm currently discovering Ragel and I am wondering when the eof
variable is required?
I understand the machines are defined to accept and consume NUL
characters. This is the reason why the params_execute function is
given strlen(argv[a])+1.
Then Ragel starts making use of the eof variable, which params.rl
doesn't define.
Can someone please explain me why removing that 0 in the machine makes
Ragel use the eof variable?
Thank you,
Gregory
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