Are there multiplatform alternatives to classes like Optiona

Question

Are there multiplatform alternatives to classes like Optional and StackOverflowError

Joffrey · Answer

`Optional` in Kotlin can just be a nullable type that s multiplatform and you benefit from a bunch of syntax features that are nicer than `Optional` s own utilities Regarding `StackOverflowError` what are you trying to do with this class in the first place

mbonnin · Answer

Unfortunately there are cases were the distinction between `null` and `undefined` could be useful We ended up defining our own `Optional` but having a standard way to do it would be nice

mbonnin · Answer

In swift you can do double optional IIRC which kindof solves the issue albeit is looking kind of weird

martmists · Answer

Nullability sadly causes some other problems in the code and the StackOverflowError is necessary to not crash when left recursion parsing goes too deep

Joffrey · Answer

Do you have examples of problems caused by nullability I think I m missing your point

Joffrey · Answer

If recursion goes too deep to the point of throwing this why would the solution be to catch the error though Shouldn t you fix the recursion issue instead

martmists · Answer

The issue is that infinite recursion is necessary for implementing a left recursive packrat parser I don t do any left memoization by default so if it ends up recursing to deep I throw a different error stating memoLeft needs to be used and in which rule it s necessary

martmists · Answer

The only other option I have is to fully analyze the code with a KSP IR plugin and generate an entire call graph and modify the IR to place memoization by default but that doesn t sound like a great solution to me personally

Joffrey · Answer

I probably don t fully understand your use case domain at hand It seems that part of the responsibility of throwing would be in user code not picking the correct library function from your code and you want nicer error handling But I m missing why you can t solve the problem my removing the potentially infinite recursion and go for an iterative parser

martmists · Answer

Often when creating a parser you ll have expressions like `expr = expr + term | term` and while this could be expanded to `term + term ` this can become increasingly big with more complex grammars and there s a good reason to want to implement it recursively as also outlined in this medium post by Guido van Rossum <https medium com gvanrossum 83706 left recursive peg grammars 65dab3c580e1>

Joffrey · Answer

Thanks Ok I think I understood your previous sentence now gt if it ends up recursing to deep I throw a different error stating memoLeft needs to be used and in which rule it s necessary I thought `memoLeft` was a function name leading to a different implementation of your algo So I thought your consumers users were writing code If I understand correctly now your users write grammars and your code is the parser And `memoLeft` is some sort of option that users can choose to use for some rules in the grammar is this correct

martmists · Answer

It s a bit of a mix of the two users write grammars in kotlin code but rules need to be wrapped in `memoLeft` if they have left recursion otherwise it will cause a StackOverflowError or similar on other targets in which case I want to notify the user to use `memoLeft` to avoid that problem

martmists · Answer

For example the grammar `commaList = commaList | term term` would be written as ``` private val commaList by sequence memoLeft memoLeft needed due to left recursion val l = first commaList term char val r = term $l $r String for now could be replaced with AST IR elements ```

martmists · Answer

But if the user forgets to use memoLeft it causes a StackOverflowError which I catch to alert them that they should probably use it in this case in rule `commaList`

Joffrey · Answer

Shouldn t you just impose a recursion limit like 20 30 levels and fail before the stackoverflow What if the user runs the program in a high memory environment and it runs fine and then the same thing runs with lower memory and fails

martmists · Answer

putting in arbitrary limits isn t useful to end users especially if `1 + 1 + 1 + 1 ` repeating 50 times isn t any less valid