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\function{error}
\synopsis{Generate an error condition}
\usage{error (String_Type msg}
\description
The \var{error} function generates a \slang error condition causing
the interpreter to start unwinding to top-level. It takes a single
string parameter which is displayed on the stderr output device.
The error condition may be cleared via an \var{ERROR_BLOCK} with the
\var{_clear_error} function. Consult \user-manual for more
information.
\example
#v+
define add_txt_extension (file)
{
if (typeof (file) != String_Type)
error ("add_extension: parameter must be a string");
file += ".txt";
return file;
}
#v-
\seealso{verror, _clear_error, message}
\done
\function{message}
\synopsis{Print a string onto the message device}
\usage{message (String_Type s}
\description
The \var{message} function will print the string specified by
\var{s} onto the message device.
\example
#v+
define print_current_time ()
{
message (time ());
}
#v-
\notes
The message device will depend upon the application. For example,
the output message device for the \var{jed} editor correspond to the
line at the bottom of the display window. The default message
device is the standard output device.
\seealso{vmessage, sprintf, error}
\done
\function{usage}
\synopsis{Generate a usage error}
\usage{usage (String_Type msg)}
\description
The \var{usage} function generates a usage exception and displays
\var{msg} to the message device.
\example
Suppose that some function \var{plot} plots an array of \var{x} and
\var{y} values. The such a function could be written to issue a
usage message if the wrong number of arguments were passed:
#v+
define plot ()
{
variable x, y;
if (_NARGS != 2)
usage ("plot (x, y)");
(x, y) = ();
% Now do the hard part
.
.
}
#v-
\seealso{error, message}
\done
\function{verror}
\synopsis{Generate an error condition}
\usage{verror (String_Type fmt, ...)}
\description
The \var{verror} function performs the same role as the \var{error}
function. The only difference is that instead of a single string
argument, \var{verror} takes a sprintf style argument list.
\example
#v+
define open_file (file)
{
variable fp;
fp = fopen (file, "r");
if (fp == NULL) verror ("Unable to open %s", file);
return fp;
}
#v-
\notes
In the current implementation, strictly speaking, the \var{verror}
function is not an intrinsic function. Rather it is a predefined
\slang function using a combination of \var{Sprintf} and
\var{error}.
\seealso{error, Sprintf, vmessage}
\done
\function{vmessage}
\synopsis{Print a formatted string onto the message device}
\usage{vmessage (String_Type fmt, ...)}
\description
The \var{vmessage} function formats a sprintf style argument list
and displays the resulting string onto the message device.
\notes
In the current implementation, strictly speaking, the \var{vmessage}
function is not an intrinsic function. Rather it is a predefined
\slang function using a combination of \var{Sprintf} and
\var{message}.
\seealso{message, Sprintf, verror}
\done
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