A keyboard interrupt or any error enters the user into the debugger
which provides a superset of the commands available at top-level.
The following are debugger specific commands:
| ,up |  | K | 
|  | goes up one level. |  | 
| ,top |  | K | 
|  | goes to top level. |  | 
| ,restarts |  | K | 
|  | lists available restarts |  | 
| ,restart | ,n | K | 
|  | chooses available restart. |  | 
| ,handlers | ,n | K | 
|  | shows available handlers. |  | 
| ,backtrace |  | K | 
|  | prints out called functions and their arguments. |  | 
| ,bt |  | K | 
|  | prints out called functions. |  | 
| ,frame | ,n | K | 
|  | prints out nth called function and its arguments. |  | 
| ,frame-var | ,n ,name | K | 
|  | prints out nth called function's parameter name. |  | 
| frame-var | (n|<int> name|<sym>) | F | 
|  | returns nth called function's parameter name. |  | 
|  |