backtrace_on - enable stack backtrace on error.Synopsis:
backtrace_on -> -Description:
This functions enables a human readable backtrace of the execution
stack. This is useful to locate where precisely an error occured. Note
that this function also disables the interpreter's tail recursion
optimization and will therefore impose a small performance
penalty. The command backtrace_off disables the stack backtrace and
re-enables tail recursion optimization.