FFI has the problem that when things go wrong in calls, or in specifications of functions, the diagnostics refer to an internal function like ffi-call or ffi-make-call-desc, which is not helpful in identifying the error. We want the diagnostics to refer to the foreign function, or foreignb callback wrapper, to which the problem pertains. The approach taken is to stick the name symbol into the ffi-call-desc object. Functions which work with a ffi-call-desc can pull out the name and use it for reporting. * ffi.c (struct txr_ffi_call_desc): Add name member. (ffi_call_desc_print_op): Include name in printed representation. (ffi_desc_mark_op): Mark the name. (ffi_make_call_desc): Take new argument to specify the name, storing it into the structure. If it is specified,then use that name for reporting errors, otherwise stick with ffi-make-call-desc. (ffi_call_wrap, ffi_closure_dispatch, ffi_closure_dispatch_safe, ffi_make_closure): Use the name from the call descriptor, or else the function's own name if that is nil. (ffi_init): Update registration of ffi-make-call-desc intrinsic to five arguments with four required. * ffi.h (ffi_make_call_desc): Declaration updated. * share/txr/stdlib/ffi.tl (deffi, deffi-cb-expander): Pass the name symbol down to ffi-make-call-desc. * txr.1: Documented.