[Haskell-cafe] layout problem
simonmar at microsoft.com
Thu Nov 17 05:24:36 EST 2005
On 16 November 2005 17:15, Christian Maeder wrote:
> Simon Peyton-Jones wrote:
>> Indeed! I always use braces and semicolons with do-notation. You
>> are free to do so too! Nothing requires you to use layout. Indeed,
>> you can freely mix the two.
> I would not recommend braces and semicolons, because these allow a bad
> layout (easy to parse for a compiler, but hard to read for a human),
> unless you invest the time to make a tidy layout despite the braces
> and semicolons. (So why not only make a tidy layout?)
> Surely, a different layout may change your semantics (in rare cases).
> A missplaced "_ -> error ..." case usually causes a pattern warning.
>>>>> liftIOTrap io =
>>>>> do mx <- liftIO (do x <- io
>>>>> return (return x)
>>>>> (\e -> return (throwError
> I'ld rather avoid the infix `catchError' and write:
> liftIO $ catchError
> (do ...
> ) $ \e ->
I generally prefer to use the "handle" variants rather than "catch":
handle my_handler $ do
x <- io
return (return x)
my_handler e = return (throwError (fromIOError e))
Don't be afraid to name things if it makes your code easier to read.
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