Hello: I'm processing a pretty big data set, but I was surprised to see SLIME fail with this message: Evaluation aborted on #<SWANK::SWANK-ERROR {1003C395A1}>. ... while the result of my computation continued to be printed on the *inferior-lisp* buffer, dispatch-event: (:WRITE-STRING "((0 0 0 0 0 0 [... 158M worth of 0's and 1's] Here is the rest of what I found there, in case it helps with debugging. (Are there any configuration options you would recommend when working with large-scale data?) Joe encode-message dispatch-event: (:RETURN #<SB-THREAD:THREAD "initial thread" RUNNING {1002900DB1}> (:ABORT "#<SWANK::SWANK-ERROR {1003C395A1}>") 230) encode-message close-connection: The value 165020663 is not of type (COMMON-LISP:UNSIGNED-BYTE 24). ... deinstall-fd-handler ;; Event history end. ;; Backtrace: 0: ((FLET SWANK-BACKEND:CALL-WITH-DEBUGGING-ENVIRONMENT) #<FUNCTION (LAMBDA #) {10A0472609}>) 1: (SWANK::SAFE-BACKTRACE) 2: (SWANK::MAKE-SWANK-ERROR #<TYPE-ERROR expected-type: (UNSIGNED-BYTE 24) datum: 165020663>)[:OPTIONAL] 3: ((FLET #:LAMBDA1275) #<TYPE-ERROR expected-type: (UNSIGNED-BYTE 24) datum: 165020663>) 4: (SIGNAL #<TYPE-ERROR expected-type: (UNSIGNED-BYTE 24) datum: 165020663>) 5: (ERROR TYPE-ERROR :DATUM 165020663 :EXPECTED-TYPE (UNSIGNED-BYTE 24)) 6: (SB-KERNEL::OBJECT-NOT-TYPE-ERROR-HANDLER ..) 7: (SB-KERNEL:INTERNAL-ERROR #.(SB-SYS:INT-SAP #X7FFFF6665E00) #<unavailable argument>) 8: ("foreign function: call_into_lisp") 9: ("foreign function: funcall2") 10: ("foreign function: interrupt_internal_error") 11: ("foreign function: #x41052B") 12: (SWANK-RPC::WRITE-HEADER #<SB-SYS:FD-STREAM for "socket 127.0.0.1:36018, peer: 127.0.0.1:34439" {1003067A01}> 165020663)[:EXTERNAL] 13: (SWANK-RPC:WRITE-MESSAGE ..) 14: (SWANK::ENCODE-MESSAGE ..) 15: (SWANK::SEND-TO-EMACS ..) 16: (SWANK::SEND-REPL-RESULTS-TO-EMACS (((0 0 0 0 0 0 ...) (0 0 0 0 0 0 ...) (0 0 0 0 0 0 ...) (0 0 1 0 0 0 ...) (0 0 0 0 0 0 ...) (0 0 0 0 0 0 ...) ...))) 17: (SWANK::TRACK-PACKAGE #<CLOSURE (LAMBDA #) {1002AFF3A9}>) 18: (SWANK::CALL-WITH-RETRY-RESTART "Retry SLIME REPL evaluation request." #<CLOSURE (LAMBDA #) {1002AFF2C9}>) 19: (SWANK::CALL-WITH-BUFFER-SYNTAX NIL #<CLOSURE (LAMBDA #) {1002AFF299}>) 20: (SWANK::REPL-EVAL ..) 21: (SB-INT:SIMPLE-EVAL-IN-LEXENV (SWANK:LISTENER-EVAL "(setq matrix (mapcar (lambda (source) ..) 22: (EVAL (SWANK:LISTENER-EVAL "(setq matrix (mapcar (lambda (source) ..) 23: (SWANK:EVAL-FOR-EMACS ..) 24: (SWANK::PROCESS-REQUESTS T) 25: ((LAMBDA ())) 26: ((LAMBDA ())) 27: (SWANK-BACKEND::CALL-WITH-BREAK-HOOK #<FUNCTION SWANK:SWANK-DEBUGGER-HOOK> #<CLOSURE (LAMBDA #) {1002AF2449}>) 28: ((FLET SWANK-BACKEND:CALL-WITH-DEBUGGER-HOOK) #<FUNCTION SWANK:SWANK-DEBUGGER-HOOK> #<CLOSURE (LAMBDA #) {1002AF2449}>) 29: (SWANK::CALL-WITH-BINDINGS ((*STANDARD-OUTPUT* . #) (*STANDARD-INPUT* . #) (*TRACE-OUTPUT* . #) (*ERROR-OUTPUT* . #) (*DEBUG-IO* . #) (*QUERY-IO* . #) ...) #<CLOSURE (LAMBDA #) {1002AF2469}>) 30: (SWANK::HANDLE-REQUESTS #<SWANK::SINGLETHREADED-CONNECTION {1004282391}> T) 31: ((LABELS SWANK-BACKEND::RUN) 7) 32: (SB-IMPL::SUB-SUB-SERVE-EVENT NIL NIL) 33: (SB-IMPL::SUB-SERVE-EVENT NIL NIL NIL) 34: (SB-SYS:WAIT-UNTIL-FD-USABLE 0 :INPUT NIL T) 35: (SB-IMPL::REFILL-INPUT-BUFFER #<SB-SYS:FD-STREAM for "standard input" {1002901141}>) 36: (SB-IMPL::INPUT-CHAR/UTF-8 #<SB-SYS:FD-STREAM for "standard input" {1002901141}> NIL #:EOF-OBJECT) 37: ((LAMBDA (&REST REST)) #<SB-SYS:FD-STREAM for "standard input" {1002901141}> NIL #:EOF-OBJECT) 38: (READ-CHAR #<SB-SYS:FD-STREAM for "standard input" {1002901141}> NIL #:EOF-OBJECT #<unused argument>) 39: (READ-CHAR #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {10001A7941}> NIL #:EOF-OBJECT #<unused argument>) 40: (SB-IMPL::%READ-PRESERVING-WHITESPACE #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {10001A7941}> NIL (NIL) T) 41: (SB-IMPL::%READ-PRESERVING-WHITESPACE #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {10001A7941}> NIL (NIL) NIL) 42: (READ #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {10001A7941}> NIL (NIL) NIL) 43: (SB-IMPL::REPL-READ-FORM-FUN #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {10001A7941}> #<unavailable argument>) 44: (SB-IMPL::REPL-FUN NIL) 45: ((LAMBDA ())) 46: (SB-IMPL::%WITH-REBOUND-IO-SYNTAX #<CLOSURE (LAMBDA #) {1003030679}>) 47: (SB-IMPL::TOPLEVEL-REPL NIL) 48: (SB-IMPL::TOPLEVEL-INIT) 49: ((FLET #:WITHOUT-INTERRUPTS-BODY-[RESTART-LISP]30)) 50: ((LABELS SB-IMPL::RESTART-LISP)) ;; Connection to Emacs lost. [ ;; condition: The value 165020663 is not of type (UNSIGNED-BYTE 24). ;; type: TYPE-ERROR ;; style: :FD-HANDLER]