biohazard-1.0.3: bioinformatics support library

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LanguageHaskell2010

Bio.Iteratee.Exception

Contents

Description

Monadic and General Iteratees: Messaging and exception handling.

Iteratees use an internal exception handling mechanism that is parallel to that provided by Exception. This allows the iteratee framework to handle its own exceptions outside IO.

Iteratee exceptions are divided into two categories, IterException and EnumException. IterExceptions are exceptions within an iteratee, and EnumExceptions are exceptions within an enumerator.

Enumerators can be constructed to handle an IterException with Data.Iteratee.Iteratee.enumFromCallbackCatch. If the enumerator detects an iteratee exception, the enumerator calls the provided exception handler. The enumerator is then able to continue feeding data to the iteratee, provided the exception was successfully handled. If the handler could not handle the exception, the IterException is converted to an EnumException and processing aborts.

Exceptions can also be cleared by Data.Iteratee.Iteratee.checkErr, although in this case the iteratee continuation cannot be recovered.

When viewed as Resumable Exceptions, iteratee exceptions provide a means for iteratees to send control messages to enumerators. The seek implementation provides an example. Data.Iteratee.Iteratee.seek stores the current iteratee continuation and throws a SeekException, which inherits from IterException. Data.Iteratee.IO.enumHandleRandom is constructed with enumFromCallbackCatch and a handler that performs an hSeek. Upon receiving the SeekException, enumHandleRandom calls the handler, checks that it executed properly, and then continues with the stored continuation.

As the exception hierarchy is open, users can extend it with custom exceptions and exception handlers to implement sophisticated messaging systems based upon resumable exceptions.

Synopsis

Exception types

data IFException Source #

Root of the Iteratee exception hierarchy. IFException derives from Control.Exception.SomeException. EnumException, IterException, and all inheritants are descendents of IFException.

Constructors

Exception e => IFException e 

class (Typeable e, Show e) => Exception e where #

Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

data MyException = ThisException | ThatException
    deriving Show

instance Exception MyException

The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
Caught ThisException

In more complicated examples, you may wish to define a whole hierarchy of exceptions:

---------------------------------------------------------------------
-- Make the root exception type for all the exceptions in a compiler

data SomeCompilerException = forall e . Exception e => SomeCompilerException e

instance Show SomeCompilerException where
    show (SomeCompilerException e) = show e

instance Exception SomeCompilerException

compilerExceptionToException :: Exception e => e -> SomeException
compilerExceptionToException = toException . SomeCompilerException

compilerExceptionFromException :: Exception e => SomeException -> Maybe e
compilerExceptionFromException x = do
    SomeCompilerException a <- fromException x
    cast a

---------------------------------------------------------------------
-- Make a subhierarchy for exceptions in the frontend of the compiler

data SomeFrontendException = forall e . Exception e => SomeFrontendException e

instance Show SomeFrontendException where
    show (SomeFrontendException e) = show e

instance Exception SomeFrontendException where
    toException = compilerExceptionToException
    fromException = compilerExceptionFromException

frontendExceptionToException :: Exception e => e -> SomeException
frontendExceptionToException = toException . SomeFrontendException

frontendExceptionFromException :: Exception e => SomeException -> Maybe e
frontendExceptionFromException x = do
    SomeFrontendException a <- fromException x
    cast a

---------------------------------------------------------------------
-- Make an exception type for a particular frontend compiler exception

data MismatchedParentheses = MismatchedParentheses
    deriving Show

instance Exception MismatchedParentheses where
    toException   = frontendExceptionToException
    fromException = frontendExceptionFromException

We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
*** Exception: MismatchedParentheses

Methods

toException :: e -> SomeException #

fromException :: SomeException -> Maybe e #

displayException :: e -> String #

Render this exception value in a human-friendly manner.

Default implementation: show.

Since: 4.8.0.0

Instances
Exception Void

Since: 4.8.0.0

Instance details
Exception PatternMatchFail

Since: 4.0

Instance details
Exception RecSelError

Since: 4.0

Instance details
Exception RecConError

Since: 4.0

Instance details
Exception RecUpdError

Since: 4.0

Instance details
Exception NoMethodError

Since: 4.0

Instance details
Exception TypeError

Since: 4.9.0.0

Instance details
Exception NonTermination

Since: 4.0

Instance details
Exception NestedAtomically

Since: 4.0

Instance details
Exception Dynamic

Since: 4.0.0.0

Instance details
Exception BlockedIndefinitelyOnMVar

Since: 4.1.0.0

Instance details
Exception BlockedIndefinitelyOnSTM

Since: 4.1.0.0

Instance details
Exception Deadlock

Since: 4.1.0.0

Instance details
Exception AllocationLimitExceeded

Since: 4.8.0.0

Instance details
Exception CompactionFailed

Since: 4.10.0.0

Instance details
Exception AssertionFailed

Since: 4.1.0.0

Instance details
Exception SomeAsyncException

Since: 4.7.0.0

Instance details
Exception AsyncException

Since: 4.7.0.0

Instance details
Exception ArrayException

Since: 4.1.0.0

Instance details
Exception FixIOException

@since TODO

Instance details
Exception ExitCode

Since: 4.1.0.0

Instance details
Exception IOException

Since: 4.1.0.0

Instance details
Exception ErrorCall

Since: 4.0.0.0

Instance details
Exception ArithException

Since: 4.0.0.0

Instance details
Exception SomeException

Since: 3.0

Instance details
Exception UnicodeException 
Instance details
Exception IterStringException # 
Instance details
Exception EofException # 
Instance details
Exception SeekException # 
Instance details
Exception IterException # 
Instance details
Exception EnumUnhandledIterException # 
Instance details
Exception EnumStringException # 
Instance details
Exception DivergentException # 
Instance details
Exception EnumException # 
Instance details
Exception IFException # 
Instance details
Exception Timeout

Since: 4.7.0.0

Instance details

Methods

toException :: Timeout -> SomeException #

fromException :: SomeException -> Maybe Timeout #

displayException :: Timeout -> String #

Exception AsyncCancelled 
Instance details

Methods

toException :: AsyncCancelled -> SomeException #

fromException :: SomeException -> Maybe AsyncCancelled #

displayException :: AsyncCancelled -> String #

Exception ExceptionInLinkedThread 
Instance details

Methods

toException :: ExceptionInLinkedThread -> SomeException #

fromException :: SomeException -> Maybe ExceptionInLinkedThread #

displayException :: ExceptionInLinkedThread -> String #

Exception ParseError # 
Instance details
Exception ZLibException # 
Instance details
Exception ZLibParamsException # 
Instance details
Exception DecompressError 
Instance details

Methods

toException :: DecompressError -> SomeException #

fromException :: SomeException -> Maybe DecompressError #

displayException :: DecompressError -> String #

Enumerator exceptions

Iteratee exceptions

Functions

enStrExc :: String -> EnumException Source #

Create an EnumException from a string.

iterStrExc :: String -> SomeException Source #

Create an iteratee exception from a string. This convenience function wraps IterStringException and toException.

wrapIterExc :: IterException -> EnumException Source #

Convert an IterException to an EnumException. Meant to be used within an Enumerator to signify that it could not handle the IterException.