mylang | A simple programming language inspired by Python | Interpreter library

These sort of questions should be answered in the documentation for the tool. But I couldn't find them there :-( I don't have a lot of experience with BNFC, either, so be cautious applying this answer.

1. psProc calls the lexer's scan_string interface, and that interface makes a copy of the provided string. Flex likes to modify the input as it tokenises, so it can only deal with const char* inputs by copying them. So the string could have been freed immediately after the call to scan_string, but psProc parses the entire input before returning so you don't have anyway to do that. You can certainly free the string when psProc returns.

   I doubt whether this is an issue for you, but if you are planning on parsing very large in-memory strings, you might want to consider using fmemopen (at least, on Posix platforms) to open the string as a FILE*. That doesn't avoid the copy, but it does it in chunks of 8k or so, which avoids keeping two copies of the entire string during the parse.

2. I have no idea how BNFC expects you to free parse tree nodes. (In fact, I rather suspect that it doesn't expect you to do that.) The nodes are linked with internal pointers, and it would certainly be possible to write an AST walker which free'd all the nodes recursively using a post-order traverse. But I don't see any generated code which does that. Perhaps I haven't looked hard enough.

   Calling free() on the top-level node will just free one node. The rest of the tree will then be leaked, since no other pointers to it exist.

3. I'm pretty sure your suspicion about thread safety are correct. The global is assigned to by the reduction action for the Proc production, and then later returned by psProc. There's no locking, so if there were another parser in another thread, the global could get overwritten. The global is just a pointer to the node which is to be returned, and the node itself should be thread-safe, since it is dynamically-allocated by the parser thread. So you could probably change the declaration of the global(s) to use thread-local storage, but that would have to be done by postprocessing the generated code.

What you are trying to do is possible by using DynamicResource like you did for TextBlock:

Each rule is sort-checked at kompile time to be sort-preserving, so it's not needed to check this at runtime. If something of the correct sort goes in, something of the correct sort comes out.

The cell gets sort K, at least for example, in this definition: https://github.com/kframework/evm-semantics/blob/272608d70f363ed3d8d921887b98a26102a03032/evm.md#configuration

it results in compiled.txt (found at .build/defn/java/driver-kompiled/compiled.txt) which looks like:

You're using getChild(1) to access the argument of the print statement. This will give you a TerminalNode containing either an ID or STRLIT token. You can access the token using the getSymbol() method and you can then access the token's type using the .type property. The type will be a number that you can compare against constants like MyLanguageParser.ID or MyLanaguageParser.STRLIT.

Using getChild isn't necessarily the best way to access a node's children though. Each context class will have specific accessors for each of its children.

Specifically the PrintContext object will have methods ID() and STRLIT(). One of them will return null, the other will return a TerminalNode object containing the given token. So you know whether it was an ID or string literal by seeing which one isn't null.

That said, the more common solution would be to not have a union of possible kinds of arguments in the print rule, but instead allow any kind of expression as an argument to print. You can then use labelled alternatives in your expression rule to get different visitor methods for each kind of expression:

So far I am able to know field(s) type:

You need to inject mylang-js.tmLanguage.json into source.mylang as well (injectTo only applies to the top-level scope name, see explanation here):

Your main issue is on the line with

You could simply include goto in the patterns for strings:

I had to change file.split(";") to file.split("\\s*;\\s*")