# error_handler

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Module

error_handler

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Module Summary

Default system error handler.

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Description

This module defines what happens when certain types of errors occur.

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Exports

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raise_undef_exception(Module, Function, Args) -> no_return()
OTP R16B

### Types

Module = Function = atom()
Args = list()
A (possibly empty) list of arguments Arg1,..,ArgN

Raises an undef exception with a stacktrace, indicating that Module:Function/N is undefined.

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undefined_function(Module, Function, Args) -> any()

### Types

Module = Function = atom()
Args = list()
A (possibly empty) list of arguments Arg1,..,ArgN

This function is called by the runtime system if a call is made to Module:Function(Arg1,.., ArgN) and Module:Function/N is undefined. Notice that this function is evaluated inside the process making the original call.

This function first attempts to autoload Module. If that is not possible, an undef exception is raised.

If it is possible to load Module and function Function/N is exported, it is called.

Otherwise, if function '$handle_undefined_function'/2 is exported, it is called as '$handle_undefined_function'(Function, Args).

Warning

Defining '$handle_undefined_function'/2 in ordinary application code is highly discouraged. It is very easy to make subtle errors that can take a long time to debug. Furthermore, none of the tools for static code analysis (such as Dialyzer and Xref) supports the use of '$handle_undefined_function'/2 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.

Otherwise an undef exception is raised.

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undefined_lambda(Module, Fun, Args) -> term()

### Types

Module = atom()
Fun = function()
Args = list()
A (possibly empty) list of arguments Arg1,..,ArgN

This function is evaluated if a call is made to Fun(Arg1,.., ArgN) when the module defining the fun is not loaded. The function is evaluated inside the process making the original call.

If Module is interpreted, the interpreter is invoked and the return value of the interpreted Fun(Arg1,.., ArgN) call is returned.

Otherwise, it returns, if possible, the value of apply(Fun, Args) after an attempt is made to autoload Module. If this is not possible, the call fails with exit reason undef.

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Notes

The code in error_handler is complex. Do not change it without fully understanding the interaction between the error handler, the init process of the code server, and the I/O mechanism of the code.

Code changes that seem small can cause a deadlock, as unforeseen consequences can occur. The use of input is dangerous in this type of code.