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## What is Debugger

A debugger `dbx` is available for C programs on `Sun`, `VAX` etc. In `dbx`, one can use commands such as setting break-point on a source line, stepwise execution, inspecting a variable's value etc. Asir provides such a `dbx`-like debugger. In addition to such commands, we adopted several useful commands from `gdb`. In order to enter the debug-mode, type `debug;` at the top level of Asir.

    [10] debug;
    (debug)

`Asir` also enters the debug-mode by the following means or in the following situations.

- When it reaches a break point while executing a program.
- When the ``d'` option is selected at an interruption.
- When it detects errors while executing a program. In this case, to continue the execution of the program is impossible. But because it reports the statement in the user defined function that caused the error, then enters the debug-mode, user can inspect the values of variables at the error state. This helps to analyze the error and debug the program.
- When built-in function `error()` is called.

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