arithy
commented
3 years ago I answer your questions.
- What is the storage duration of
$$? There's actually a StackOverflow question about this. https://stackoverflow.com/questions/66145396/how-to-use-the-value-returned-by-a-packcc-parser
$$ values of respective rules are kept so that parsing can be done without any problem.
Users don't need to care about their storage duration.
Note that it is responsibility of users to release system resources like memory blocks associated with $$ after parsing.
As for the question in stackoverflow, the problem is not of the storage duration of $$ but that of the string $1 created by PackCC.
The explanation about it is already in README, which says 'Note that the string data held by $n and $0 are discarded immediately after evaluation of the action'.
- How can I read from a file instead of stdin?
Use the function macro PCC_GETCHAR(auxil).
#define PCC_GETCHAR(auxil) get_character((auxil)->input)Here, the user function get_character((auxil)->input) returns a character retrieved from (auxil)->input, which holds the information of the text input source.
The argument auxil is a pointer to a user-defined structure.
As instructed in README, its data type can be specified by %auxil directive and its value can be fed via the argument auxil of the API function pcc_create().
- Suppose I want to generate an AST. Am I supposed to generate it with $$ inside the rules manually? Is there some way to make this easier? Or is generating an AST beyond the scope of this parser generator?
An AST node can be retained by using $$ as a pointer to it.
Simplified example is shown below.
Specification of the data type of $$:
%value "MyASTNode *"Here, MyASTNode is some structure type defined by a user.
AST node creation in an action:
$$ = MyASTNode_create(auxil);Here, the function MyASTNode_create() returns a pointer to an AST node newly created.
To free the memory used by the AST nodes later, a user-defined structure auxil should retain their pointers.
- Can I define an action and an error action on the same rule?
Yes. There is no restriction.
- What's the deal with whitespace? It seems to be ignored. What if my language were whitespace-sensitive? Does it suck the whitespace out of string literals?
Yes. Use string literals, where white-spaces are not ignored. Strings without quotation are interpreted as names of rules.
- My language has C style single and multi-line comments in it. How can I ignore those like whitespace seems to be ignored?
Use the rules as below.
_ <- ( space / comment )*
comment <- '/*' ( / !'*/' . )* '*/'
space <- blank / end_of_line
blank <- [ \t\v\f]
end_of_line <- '\r\n' / '\n' / '\r'Here, the rule _ represents white-spaces and comment blocks.
--
I think that your questions arise mainly because of lack of some practical example. I'm preparing an example to create some AST now.
ccleve
apaz-cli
Questions
These are things that I've been wondering. Other people probably have the same questions, so they should probably be covered in the README.
What is the storage duration of
$$? There's actually a StackOverflow question about this. https://stackoverflow.com/questions/66145396/how-to-use-the-value-returned-by-a-packcc-parserHow can I read from a file instead of stdin?
Suppose I want to generate an AST. Am I supposed to generate it with $$ inside the rules manually? Is there some way to make this easier? Or is generating an AST beyond the scope of this parser generator?
Can I define an action and an error action on the same rule?
What's the deal with whitespace? It seems to be ignored. What if my language were whitespace-sensitive? Does it suck the whitespace out of string literals?
My language has C style single and multi-line comments in it. How can I ignore those like whitespace seems to be ignored?
Thanks, and you've got a very impressive project.