.TH error_handler 3erl "kernel 9.2" "Ericsson AB" "Erlang Module Definition"
.SH NAME
error_handler \- Default system error handler.
.SH DESCRIPTION
.LP
This module defines what happens when certain types of errors occur\&.
.SH EXPORTS
.LP
.nf

.B
raise_undef_exception(Module, Function, Args) -> no_return()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Module = Function = atom()
.br
Args = list()
.br
.RS 2
 A (possibly empty) list of arguments \fIArg1,\&.\&.,ArgN\fR\&
.RE
.RE
.RE
.RS
.LP
Raises an \fIundef\fR\& exception with a stacktrace, indicating that \fIModule:Function/N\fR\& is undefined\&.
.RE

.LP
.nf

.B
undefined_function(Module, Function, Args) -> any()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Module = Function = atom()
.br
Args = list()
.br
.RS 2
 A (possibly empty) list of arguments \fIArg1,\&.\&.,ArgN\fR\&
.RE
.RE
.RE
.RS
.LP
This function is called by the runtime system if a call is made to \fIModule:Function(Arg1,\&.\&., ArgN)\fR\& and \fIModule:Function/N\fR\& is undefined\&. Notice that this function is evaluated inside the process making the original call\&.
.LP
This function first attempts to autoload \fIModule\fR\&\&. If that is not possible, an \fIundef\fR\& exception is raised\&.
.LP
If it is possible to load \fIModule\fR\& and function \fIFunction/N\fR\& is exported, it is called\&.
.LP
Otherwise, if function \fI\&'$handle_undefined_function\&'/2\fR\& is exported, it is called as \fI\&'$handle_undefined_function\&'(\fR\&Function, Args)\&.
.LP

.RS -4
.B
Warning:
.RE
Defining \fI\&'$handle_undefined_function\&'/2\fR\& in ordinary application code is highly discouraged\&. It is very easy to make subtle errors that can take a long time to debug\&. Furthermore, none of the tools for static code analysis (such as Dialyzer and Xref) supports the use of \fI\&'$handle_undefined_function\&'/2\fR\& and no such support will be added\&. Only use this function after having carefully considered other, less dangerous, solutions\&. One example of potential legitimate use is creating stubs for other sub-systems during testing and debugging\&.

.LP
Otherwise an \fIundef\fR\& exception is raised\&.
.RE

.LP
.nf

.B
undefined_lambda(Module, Fun, Args) -> term()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Module = atom()
.br
Fun = function()
.br
Args = list()
.br
.RS 2
 A (possibly empty) list of arguments \fIArg1,\&.\&.,ArgN\fR\&
.RE
.RE
.RE
.RS
.LP
This function is evaluated if a call is made to \fIFun(Arg1,\&.\&., ArgN)\fR\& when the module defining the fun is not loaded\&. The function is evaluated inside the process making the original call\&.
.LP
If \fIModule\fR\& is interpreted, the interpreter is invoked and the return value of the interpreted \fIFun(Arg1,\&.\&., ArgN)\fR\& call is returned\&.
.LP
Otherwise, it returns, if possible, the value of \fIapply(Fun, Args)\fR\& after an attempt is made to autoload \fIModule\fR\&\&. If this is not possible, the call fails with exit reason \fIundef\fR\&\&.
.RE

.SH "NOTES"

.LP
The code in \fIerror_handler\fR\& is complex\&. Do not change it without fully understanding the interaction between the error handler, the \fIinit\fR\& process of the code server, and the I/O mechanism of the code\&.
.LP
Code changes that seem small can cause a deadlock, as unforeseen consequences can occur\&. The use of \fIinput\fR\& is dangerous in this type of code\&.