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### `error`

`error(message)`
  :: Forces Asir to cause an error and enter debugging mode.

message
  string

- When Asir encounters a serious error such that it finds difficult to continue execution, it, in general, tries to enter debugging mode before it returns to top level. The command `error()` forces a similar behavior in a user program.
- The argument is a string which will be displayed when `error()` will be executed.
- You can enter the debug-mode when your program encounters an illegal value for a program variable, if you have written the program so as to call `error()` upon finding such an error in your program text.

    % cat mod3
    def mod3(A) {
            if ( type(A) >= 2 )
                    error("invalid argument");
            else
                    return A % 3;
    }
    end$
    % asir
    [0] load("mod3");
    1
    [3] mod3(5);
    2
    [4] mod3(x);
    invalid argument
    stopped in mod3 at line 3 in file "./mod3"
    3                       error("invalid argument");
    (debug) print A
    A = x
    (debug) quit
    return to toplevel
    [4]

`References`
  section `debug`.

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