 | Gtk2Hs | Contents | Index |
| System.Glib.GError |
|
| Contents |
Error Reporting, glib's system for reporting errors.
GErrors are used by glib to report recoverable runtime errors.
This module provides functions for checking glib/gtk functions that report GErrors. It also provides functions for throwing and catching GErrors as Haskell exceptions.
| data GError = GError !GErrorDomain !GErrorCode !GErrorMessage | |
| type GErrorDomain = GQuark | |
| type GErrorCode = Int | |
| type GErrorMessage = String | |
| catchGError :: IO a -> (GError -> IO a) -> IO a | |
| catchGErrorJust :: GErrorClass err => err -> IO a -> (GErrorMessage -> IO a) -> IO a | |
| catchGErrorJustDomain :: GErrorClass err => IO a -> (err -> GErrorMessage -> IO a) -> IO a | |
| handleGError :: (GError -> IO a) -> IO a -> IO a | |
| handleGErrorJust :: GErrorClass err => err -> (GErrorMessage -> IO a) -> IO a -> IO a | |
| handleGErrorJustDomain :: GErrorClass err => (err -> GErrorMessage -> IO a) -> IO a -> IO a | |
| failOnGError :: IO a -> IO a | |
| throwGError :: GError -> IO a | |
| class Enum err => GErrorClass err where | |
| |
| propagateGError :: (Ptr (Ptr ()) -> IO a) -> IO a | |
| checkGError :: (Ptr (Ptr ()) -> IO a) -> (GError -> IO a) -> IO a |
| A GError consists of a domain, code and a human readable message. | ||
| Constructors | ||
| ||
 Instances | ||
To catch GError exceptions thrown by Gtk2Hs functions use the catchGError* or handleGError* functions. They work in a similar way to the standard catch and handle functions.
catchGError / handleGError catches all GError exceptions, you provide a handler function that gets given the GError if an exception was thrown. This is the most general but is probably not what you want most of the time. It just gives you the raw error code rather than a Haskell enumeration of the error codes. Most of the time you will only want to catch a specific error or any error from a specific error domain. To catch just a single specific error use catchGErrorJust / handleGErrorJust. To catch any error in a particular error domain use catchGErrorJustDomain / handleGErrorJustDomain
| :: IO a | The computation to run |
| -> (GError -> IO a) | Handler to invoke if an exception is raised |
| -> IO a | |
This will catch any GError exception. The handler function will receive the raw GError. This is probably only useful when you want to take some action that does not depend on which GError exception has occured, otherwise it would be better to use either catchGErrorJust or catchGErrorJustDomain. For example: catchGError
(do ...
...)
(\(GError dom code msg) -> fail msg)
| |
| :: GErrorClass err | |
| => err | The error to catch |
| -> IO a | The computation to run |
| -> (GErrorMessage -> IO a) | Handler to invoke if an exception is raised |
| -> IO a | |
This will catch just a specific GError exception. If you need to catch a range of related errors, catchGErrorJustDomain is probably more appropriate. Example: do image <- catchGErrorJust PixbufErrorCorruptImage
loadImage
(\errorMessage -> do log errorMessage
return mssingImagePlaceholder)
| |
| :: GErrorClass err | |
| => IO a | The computation to run |
| -> (err -> GErrorMessage -> IO a) | Handler to invoke if an exception is raised |
| -> IO a | |
Catch all GErrors from a particular error domain. The handler function should just deal with one error enumeration type. If you need to catch errors from more than one error domain, use this function twice with an appropriate handler functions for each. catchGErrorJustDomain
loadImage
(\err message -> case err of
PixbufErrorCorruptImage -> ...
PixbufErrorInsufficientMemory -> ...
PixbufErrorUnknownType -> ...
_ -> ...)
| |
A verson of catchGError with the arguments swapped around.
handleGError (\(GError dom code msg) -> ...) $ ...
- Note, these functions are only useful to implementors
If you are wrapping a new API that reports GErrors you should probably use propagateGError to convert the GError into an exception. You should also note in the documentation for the function that it throws GError exceptions and the Haskell enumeration for the expected glib GError domain(s), so that users know what exceptions they might want to catch.
If you think it is more appropriate to use an alternate return value (eg Either/Maybe) then you should use checkGError.
Each error domain's error enumeration type should be an instance of this class. This class helps to hide the raw error and domain codes from the user. This interface should be implemented by calling the approrpiate {error_domain}_error_quark. It is safe to use a pure FFI call for this. Example for PixbufError: instance GErrorClass PixbufError where
gerrorDomain _ = {#call pure unsafe pixbuf_error_quark#}
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| Methods | ||||||
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| Instances | ||||||
Glib functions which report GErrors take as a parameter a GError **error. Use this function to supply such a parameter. It checks if an error was reported and if so throws it as a Haskell exception.
Example of use:
propagateGError $ \gerrorPtr ->
{# call g_some_function_that_might_return_an_error #} a b gerrorPtr
Like propagateGError but instead of throwing the GError as an exception handles the error immediately using the supplied error handler.
Example of use:
checkGError
(\gerrorPtr -> {# call g_some_function_that_might_return_an_error #} a b gerrorPtr)
(\(GError domain code msg) -> ...)