gdb also has DAP nowadays. I’d also try to get a full backtrace (enable elisp debugging).

If you grow tired of trying to use DAP then I’d suggest using gdb in conjunction with gf2: https://github.com/nakst/gf

gf2 is an extremely fast front-end for gdb.

Very cool! So this library leverages SBCL’s ability to have specialized arrays of single-floats (for example)? If U-A-E-T returns T then you’ll suffer the cost of dereferencing a pointer for each object otherwise.