bluefin-0.6.0.0: The Bluefin effect system
Safe HaskellNone
LanguageHaskell2010

Bluefin.Capability.Throw

Synopsis

Capability

type Throw = Exception #

Capability to throw an exception of type exn

Handlers

try #

Arguments

:: forall exn (es :: Effects) a. (forall (e :: Effects). Exception exn e -> Eff (e :& es) a) 
-> Eff es (Either exn a)

Left if the exception was thrown, Right otherwise

>>> runPureEff $ try $ \e -> do
      throw e 42
      pure "No exception thrown"
Left 42

handle #

Arguments

:: forall exn (es :: Effects) a. (exn -> Eff es a)

If the exception is thrown, apply this handler

-> (forall (e :: Effects). Exception exn e -> Eff (e :& es) a) 
-> Eff es a 
>>> runPureEff $ handle (pure . show) $ \e -> do
      throw e 42
      pure "No exception thrown"
"42"

catch #

Arguments

:: forall exn (es :: Effects) a. (forall (e :: Effects). Exception exn e -> Eff (e :& es) a) 
-> (exn -> Eff es a)

If the exception is thrown, apply this handler

-> Eff es a 

handle, but with the argument order swapped

Effectful operations

throw #

Arguments

:: forall (e :: Effects) (es :: Effects) ex a. e <: es 
=> Exception ex e 
-> ex

Value to throw

-> Eff es a 
>>> runPureEff $ try $ \e -> do
      throw e 42
      pure "No exception thrown"
Left 42

>>> runPureEff $ try $ \e -> do
      pure "No exception thrown"
Right "No exception thrown"

rethrowIO #

Arguments

:: forall ex (es :: Effects) (e1 :: Effects) (e2 :: Effects) r. (e1 <: es, e2 <: es, Exception ex) 
=> IOE e1 
-> Exception ex e2 
-> Eff es r 
-> Eff es r

͘

Rethrow an exception raised by an IO action as a Bluefin exception.

runEff $ \io -> do
  r <- try $ \ex -> do
    rethrowIO @IOException io ex $ do
      effIO io (readFile "/tmp/doesnt-exist")

  effIO io $ putStrLn $ case r of
    Left e -> "Caught IOException:\n" ++ show e
    Right contents -> contents

Caught IOException:
/tmp/doesnt-exist: openFile: does not exist (No such file or directory)