feat: add FilePath.handle

[sockmaster27]

Fixes #9032

[sockmaster27]

@magnus-madsen
Is this the correct approach

[magnus-madsen]

Yes, but please use new Java IO (nio).

https://docs.oracle.com/javase/8/docs/api/index.html?java/nio/file/Path.html
https://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#exists-java.nio.file.Path-java.nio.file.LinkOption...-

[sockmaster27]

@magnus-madsen
So like this?

[magnus-madsen]

Approximately like so:

    pub def handle(f: a -> b \ ef): a -> Result[IOError, b] \ (ef - FilePath) + IO = x ->
        try {
            Ok(f(x))
        } with FilePath {
            def exists(f, k) = {
                try {
                    k(Files.exists(Paths.get(f), (...{}: Vector[LinkOption])))
                } catch {
                    case ex: IOException => Err(IOError.Generic(ex.getMessage()))
                }
            }
        }

Note also the use of IOException.

[sockmaster27]

Approximately like so:

    pub def handle(f: a -> b \ ef): a -> Result[IOError, b] \ (ef - FilePath) + IO = x ->
        try {
            Ok(f(x))
        } with FilePath {
            def exists(f, k) = {
                try {
                    k(Files.exists(Paths.get(f), (...{}: Vector[LinkOption])))
                } catch {
                    case ex: IOException => Err(IOError.Generic(ex.getMessage()))
                }
            }
        }

Note also the use of IOException.

Wouldn't this catch other unrelated exceptions thrown by the continuation?

[sockmaster27]

Note also the use of IOException.

What about the InvalidPathException?

[magnus-madsen]

Note also the use of IOException.

What about the InvalidPathException?

Good catch, add it too.

[sockmaster27]

Actually, it looks like this doesn't throw an IOException at all 😵‍💫.
However, Files.exists throws a SecurityException.

[magnus-madsen]

We ignore security exceptions. The Files class throws IOExs on general.

[magnus-madsen]

Anyway, I think you look at each Files.X op, add its exceptions (except for SecurityEx) plus the InvalidPath thing and that is what you should catch.

[magnus-madsen]

So with that I think it should be possible to fill out this handler. And then we can iterate.

[sockmaster27]

Approximately like so:

    pub def handle(f: a -> b \ ef): a -> Result[IOError, b] \ (ef - FilePath) + IO = x ->
        try {
            Ok(f(x))
        } with FilePath {
            def exists(f, k) = {
                try {
                    k(Files.exists(Paths.get(f), (...{}: Vector[LinkOption])))
                } catch {
                    case ex: IOException => Err(IOError.Generic(ex.getMessage()))
                }
            }
        }

Note also the use of IOException.

Wouldn't this catch other unrelated exceptions thrown by the continuation?

What about this?

[magnus-madsen]

That's ok for now. We will deal with that later when we add support for java exceptions to the effect system.

[sockmaster27]

@magnus-madsen
This good?

[magnus-madsen]

Don't extend IOError. We can do it later, but doing it now causes breakages.
Second, no reason to use varargs where there is no problem. (The problem is only if the varargs array type is an interface).

[sockmaster27]

I assume it's okay now?
Then I will start to implement it for the other operations

[sockmaster27]

I assume handling OutOfMemoryException is also out of scope?

[magnus-madsen]

I assume it's okay now? Then I will start to implement it for the other operations

Please go ahead.

[magnus-madsen]

@sockmaster27 This looks almost ready? If the list() operation is giving trouble, we could defer it.

[sockmaster27]

I got list to work by using the old java.io.File. I guess we might be able to fix it later, but this should work for now.

[magnus-madsen]

I got list to work by using the old java.io.File. I guess we might be able to fix it later, but this should work for now.

That's acceptable. We prefer nio, but its totally OK to use file if necessary. Similarly to using FileReader etc.

[magnus-madsen]

Looks good: I suggest to next duplicate and split or split and duplicate, if you prefer.

[magnus-madsen]

In parallel you can also start looking into the Http effect. The design there is less clear, though.