# Exceptions handling - InMo Docs
Single documentation place for all Insanus Mokrassar libraries
Author: Ovsiannikov Aleksei

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# Exceptions handling

Unfortunatelly, exceptions handling in this library is a bit difficult in some places, but that have at least two reasons: flexibility and usability.

## “In place” handling

In case you know, where exceptions are happening, you may use several tools for exceptions catching:

- Catching with result
- Catching with callback

### Catching with result

If you prefer to receive `Result` objects instead of some weird callbacks, you may use the next syntax:

    safelyWithResult {
        // do something
    }.onSuccess { // will be called if everything is right
        // handle success
    }.onFailure { // will be called if something went wrong
        // handle error
        it.printStackTrace()
    }.getOrThrow() // will return value or throw exception

### Catching with callback

Also there is more simple (in some cases) way to handle exceptions with callbacks:

    safely(
      {
          // handle error
          it.printStackTrace()
          null // return value
      }
    ) {
        // do something
    }

### Bonus: different types of handling

There are two types of handling:

- Just safely - when you are using something to obviously retrieve value or throw exception. When handling callback has been skipped, it will throw exception by default. For example:

      safely(
          {
              it.printStackTrace()
              "error"
          }
      ) {
          error("Hi :)") // emulate exception throwing
          "ok"
      } // result will be with type String

- Safely without exceptions - almost the same as `safely`, but this type by default allow to return nullable value (when exception was thrown) instead of just throwing (as with `safely`):

      safelyWithouExceptions {
          // do something
      } // will returns nullable result type

## Global exceptions handling

The most simple way to configure exceptions handling is to change `CoroutineContext` when you are creating your `CoroutineScope` for bot processing:

    val bot = telegramBot("TOKEN")

    bot.buildBehaviour (
        scope = scope,
        defaultExceptionsHandler = {
            it.printStackTrace()
        }
    ) {
        // ...
    }

OR

    val bot = telegramBotWithBehaviour (
        "TOKEN",
        scope = scope,
        defaultExceptionsHandler = {
            it.printStackTrace()
        }
    ) {
        // ...
    }

Here we have used `ContextSafelyExceptionHandler` class. It will pass default handling of exceptions and will call the block in most cases when something inside of your bot logic has thrown exception.