Read S4 objects

[ofajardo]

Many times RData or RDs files contain objects that can be interpreted in R only if a particular 3rd party package/library is loaded. When you try to read one of these files in R, you see that those libraries are being loaded automatically.

These files can of course not be read with librdata, but right now librdata gives back the very generic error "Unable to read from file". It would be nice if one could get a more specific error for these cases.

Attached two example files involving two different libraries (tweeterR and MultiAssayExperiment)

R_files_with_dependencies.zip

[evanmiller]

Hi, I've added a slightly more specific error codes - probably still not helpful, but the error handler will report an error about an Unrecognized S-expression rather than a generic read error.

These files use S4 classes. I haven't figured out how to read or skip over them yet.

[ofajardo]

that's already good!, at least it will be quicker to guide users about what's happening and what is the limitation