Arithemtic error Blocky backtrace

arithmetic error FLOATING-POINT-INEXACT signalled
   [Condition of type FLOATING-POINT-INEXACT]

Restarts:
 0: [CONTINUE] Continue
 1: [RETRY] Retry SLIME REPL evaluation request.
 2: [*ABORT] Return to SLIME's top level.
 3: [REMOVE-FD-HANDLER] Remove #<SB-IMPL::HANDLER INPUT on descriptor 11: #<CLOSURE (LABELS SWANK-BACKEND::RUN :IN SWANK-BACKEND:ADD-FD-HANDLER) {1002CA621B}>>
 4: [ABORT] Exit debugger, returning to top level.

Backtrace:
  0: (SB-VM:SIGFPE-HANDLER #<unavailable argument> #.(SB-SYS:INT-SAP #X012F5370) #<unavailable argument>)
  1: ((FLET #:WITHOUT-INTERRUPTS-BODY-26592 :IN SB-SYS:INVOKE-INTERRUPTION))
  2: ((FLET SB-THREAD::EXEC :IN SB-SYS:INVOKE-INTERRUPTION))
  3: ((FLET #:WITHOUT-INTERRUPTS-BODY-26581 :IN SB-SYS:INVOKE-INTERRUPTION))
  4: (SB-SYS:INVOKE-INTERRUPTION #<CLOSURE (FLET SB-UNIX::INTERRUPTION :IN SB-SYS:ENABLE-INTERRUPT) {12F4D9B}>)
  5: (SB-SYS:INVOKE-INTERRUPTION #<CLOSURE (FLET SB-UNIX::INTERRUPTION :IN SB-SYS:ENABLE-INTERRUPT) {12F4D9B}>)[:EXTERNAL]
  6: ((FLET SB-UNIX::RUN-HANDLER :IN SB-SYS:ENABLE-INTERRUPT) 8 #.(SB-SYS:INT-SAP #X012F5370) #.(SB-SYS:INT-SAP #X012F53D8))
  7: ("foreign function: call_into_lisp")
  8: ("foreign function: funcall3")
  9: ("foreign function: interrupt_handle_now")
 10: ("foreign function: interrupt_handle_now_handler")
 11: ("foreign function: _sigtramp")
 12: ("foreign function: #x200D3012D4")
 13: ((SB-PCL::FAST-METHOD LISPBUILDER-SDL::PROCESS-TIMESTEP :AROUND (LISPBUILDER-SDL::FPS-MANAGER T)) ..)
 14: (BLOCKY::START-SESSION)
 15: (BLOCKY:BLOCKY)
 16: (SB-INT:SIMPLE-EVAL-IN-LEXENV (BLOCKY:BLOCKY) #<NULL-LEXENV>)
 17: (EVAL (BLOCKY:BLOCKY))
 18: (SWANK::EVAL-REGION "(blocky:blocky)\n")
 19: ((LAMBDA () :IN SWANK::REPL-EVAL))
 20: (SWANK::TRACK-PACKAGE #<CLOSURE (LAMBDA # :IN SWANK::REPL-EVAL) {100607235B}>)
 21: (SWANK::CALL-WITH-RETRY-RESTART "Retry SLIME REPL evaluation request." #<CLOSURE (LAMBDA # :IN SWANK::REPL-EVAL) {100607227B}>)
 22: (SWANK::CALL-WITH-BUFFER-SYNTAX NIL #<CLOSURE (LAMBDA # :IN SWANK::REPL-EVAL) {100607224B}>)
 23: (SWANK::REPL-EVAL "(blocky:blocky)\n")
 24: (SB-INT:SIMPLE-EVAL-IN-LEXENV (SWANK:LISTENER-EVAL "(blocky:blocky) ..)
 25: (EVAL (SWANK:LISTENER-EVAL "(blocky:blocky) ..)
 26: (SWANK:EVAL-FOR-EMACS (SWANK:LISTENER-EVAL "(blocky:blocky)\n") "COMMON-LISP-USER" 13)
 27: (SWANK::PROCESS-REQUESTS T)
 28: ((LAMBDA () :IN SWANK::HANDLE-REQUESTS))
 29: ((LAMBDA () :IN SWANK::HANDLE-REQUESTS))
 30: (SWANK-BACKEND::CALL-WITH-BREAK-HOOK #<FUNCTION SWANK:SWANK-DEBUGGER-HOOK> #<CLOSURE (LAMBDA # :IN SWANK::HANDLE-REQUESTS) {100606EDAB}>)
 31: ((FLET SWANK-BACKEND:CALL-WITH-DEBUGGER-HOOK :IN "/Applications/slime/swank-sbcl.lisp") #<FUNCTION SWANK:SWANK-DEBUGGER-HOOK> #<CLOSURE (LAMBDA # :IN SWANK::HANDLE-REQUESTS) {100606EDAB}>)
 32: (SWANK::CALL-WITH-BINDINGS ..)
 33: (SWANK::HANDLE-REQUESTS #<SWANK::SINGLETHREADED-CONNECTION {1002CA6123}> T)
 34: ((LABELS SWANK-BACKEND::RUN :IN SWANK-BACKEND:ADD-FD-HANDLER) 11)
 35: (SB-IMPL::SUB-SUB-SERVE-EVENT NIL NIL)
 36: (SB-IMPL::SUB-SERVE-EVENT NIL NIL NIL)
 37: (SB-SYS:WAIT-UNTIL-FD-USABLE 0 :INPUT NIL T)
 38: (SB-IMPL::REFILL-INPUT-BUFFER #<SB-SYS:FD-STREAM for "standard input" {10029012C3}>)
 39: (SB-IMPL::INPUT-CHAR/ASCII #<SB-SYS:FD-STREAM for "standard input" {10029012C3}> NIL #:EOF-OBJECT)
 40: ((LAMBDA (&REST REST) :IN SB-IMPL::GET-EXTERNAL-FORMAT) #<SB-SYS:FD-STREAM for "standard input" {10029012C3}> NIL #:EOF-OBJECT)
 41: (READ-CHAR #<SB-SYS:FD-STREAM for "standard input" {10029012C3}> NIL #:EOF-OBJECT #<unused argument>)
 42: (READ-CHAR #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {1000179013}> NIL #:EOF-OBJECT #<unused argument>)
 43: (SB-IMPL::%READ-PRESERVING-WHITESPACE #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {1000179013}> NIL (NIL) T)
 44: (SB-IMPL::%READ-PRESERVING-WHITESPACE #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {1000179013}> NIL (NIL) NIL)
 45: (READ #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {1000179013}> NIL (NIL) NIL)
 46: (SB-IMPL::REPL-READ-FORM-FUN #<SYNONYM-STREAM :SYMBOL SB-SYS:*STDIN* {1000179013}> #<unavailable argument>)
 47: (SB-IMPL::REPL-FUN NIL)
 48: ((LAMBDA () :IN SB-IMPL::TOPLEVEL-REPL))
 49: (SB-IMPL::%WITH-REBOUND-IO-SYNTAX #<CLOSURE (LAMBDA # :IN SB-IMPL::TOPLEVEL-REPL) {100418ACCB}>)
 50: (SB-IMPL::TOPLEVEL-REPL NIL)
 51: (SB-IMPL::TOPLEVEL-INIT)
 52: ((FLET #:WITHOUT-INTERRUPTS-BODY-241277 :IN SAVE-LISP-AND-DIE))
 53: ((LABELS SB-IMPL::RESTART-LISP :IN SAVE-LISP-AND-DIE))