The M3 Core module returns a sort of simplified loc representation in Rascal. For instance, a method in file MapParser might have the loc: |java+method:///MapParser/a()|.
However, this is evidently different from the other loc scheme I tend to see, which would look more or less like: |project://main-scheme/src/tests/MapParser.java|.
This wouldn't be a problem, except that some functions only accept one scheme or another. For instance, the function appendToFile(loc file, value V...) does not accept this scheme M3 uses, and will reject it with an error like: IO("Unsupported scheme java+method").
So, how can I convert between both schemes easily? I would like to preserve all information, like highlighted sections for instance.
Cheers.
There are two differences at play here.
java+method is an logical location, and project is a physical location. I think the best way to describe their difference is that a physical location describes the location of an actual file, or a subset of an actual file. A logical location describes the location of a certain entity in the context of a bigger model. For example, a java method in a java class/project. Often logical locations can be mapped to a physical location, but that is not always true.
For m3 for example you can use resolveLocation from IO to get the actual offset in the file that the logical location points to.
Not all locations are writeable, I don't think any logical location is. But there are also physical locations that are read only. The error you are getting is generic in that sense.
Rascal does support writing in the middle of text files, most likely you do not want to use appendToFile as it will append after the location you point it too. Most likely you want to replace a section of the text with your new section, so a regular writeFile should work.
Note that you would have to recalculate all the offsets in the file after every write. So the resolved physical locations for the logical locations would be outdated, as the file has changed since constructing the m3 model and its corresponding map between logical and physical locations.
So for this use case, you might want to think of a better way. The nicest solution is using a grammar, and rewrite the parse tree's of the file, and after rewriting overwrite the old file. Note that the most recent Java grammar shipped with Rascal is for Java 5, so this might be a bit more work than you would like. Perhaps frame your goal as a new Stack Overflow question, and we'll see what other options might be applicable.