Error handling in READ_ALL_COMMANDS

[ThomasBreuer]

LibGAP's GAP_EvalString calls the kernel function READ_ALL_COMMANDS, which does the same as the GAP function READ_ALL_COMMANDS.
Consider the following GAP session.

gap> READ_ALL_COMMANDS( InputTextString( "\"" ), false, true, ViewObj );
Syntax error: String must end with " before end of file in stream:1
[ [ false,,,, "" ] ]

The syntax error message is printed to the screen, a result is returned, and the false entry in the result indicates that an error happened.

When one uses the above input via LibGAP, what is the recommended way to handle the error in the code that calls GAP_EvalString, that is, access the error message (in order to report it) and then empty the buffer?
This error handling is currently missing in the GAP-Julia integration, see oscar-system/GAP.jl/issues/580.

[fingolfin]

I think the idea was/is to set the ERROR_OUTPUT global in GAP to an output stream to which the error messages then are written. (That's not necessarily a great API, but it was the easiest to pull of on short notice back then.)

This is of course what reset_GAP_ERROR_OUTPUT does, so we can probably just use that / imitate what error_handler does?

[ThomasBreuer]

Yes, calling error_handler in the function that calls GAP_EvalString solves the problem.