errors returned from pcall contains serialized binaries

[markmeeus]

after running this code:

result, error = pcall(function()     
  ipairs("hello")
end)

The error variable contains badarg in ipairs: [<<104,101,108,108,111>>]

Expected: badarg in ipairs: ["hello"]

The reason for this formatting is that the format_error uses ~w formatting.

format_error({badarg,Where,As}) ->
    io_lib:format("badarg in ~w: ~w", [Where,As]);

Would it be possible to use ~s in the error formatting functions?

format_error({badarg,Where,As}) ->
    io_lib:format("badarg in ~s: ~s", [Where,As]);

[rvirding]

The trouble is that the value of the of the arguments can be any valid Lua data type. Try:

result, error = pcall(function()     
  ipairs(dofile)
end)

return result, error

[markmeeus]

Ah yes, I see, the format throws argument errors when the format param is not compatible.
I think I was expecting an elixir 'inspect' type of formatting there.

So to fix this we would need format_argument type of functions for every possible argument type that goes into the io_lib:format. These would then format the structure to a string, (maybe with a default implementation using a plain ~w)
And then use the string format?

So that the format_error would look like this:

format_error({badarg,Where,As}) ->
    io_lib:format("badarg in ~s: ~s", [format_where(Where), format_args(As)]);

[rvirding]

You have discovered another bug which needs fixing first. 😄 The ipairs function never checks its argument and always succeeds, it is the function which it returns which checks that its argument is a table.

I will fix that first and then we can get back to the error message from pcall. I have some ideas about that.

[rvirding]

The ipairs and pairs handling of arguments has now been fixed.

[rvirding]

One thing is that the current get_stacktrace function is really designed to build a "better" current stack and not really print it out. That could be another function.

[markmeeus]

The thing is that this formatting happens in the pcall, so these binaries are returned to the lua code. These users may not be familiar to these erlang binary format .

[rvirding]

This has now been fixed a commit in the develop branch dd78ff5