* (1+ "a")

debugger invoked on a TYPE-ERROR in thread
#<THREAD "main thread" RUNNING {100215E4F3}>:
  The value
    "a"
  is not of type
    NUMBER
  when binding SB-KERNEL::X

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

(SB-KERNEL:TWO-ARG-+ "a" 1) [external]
0]