Catching Run Time Errors

  Psd tries to detect any run time errors before they are encountered. Before every call to an essential procedure in R4RS, it checks the number of arguments and their types. If a run time error would occur, psd stops execution and lets the user inspect and modify the environment. In order to continue, use the debugger command r and give a value that is to be returned as the result of the call. This works of course only if the code where the call is made from is being debugged.