[Haskell-cafe] Advice needed on how to improve some code

[Andrew Butterfield]

> On 16 Apr 2015, at 09:22, Tom Ellis <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:
> 
> I rather like the >>= invocations.  `do` notation would require naming
> intermediate variables.

But the >>= requires such intermediate variables anyway: all the pl' after the \  
> 
>> On Wed, Apr 15, 2015 at 8:57 PM, Jeff <jeff at datalinktech.com.au> wrote:
>> 
>>>            return pl ) >>=
>>>      ( \pl' -> let pld = P.payloadData pl' in
>>>                 if testBit mdm ( fromEnum D.GPS )
>>>                   then
>>>                     parseDeviceGPSData >>=
>>>                     ( \s -> return ( pl' { P.payloadData = pld {
>>> P.gpsData = Just s } } ) )
>>>                   else
>>>                     return pl' ) >>=
>>>      ( \pl' -> let pld = P.payloadData pl' in
>>>                 if testBit mdm ( fromEnum D.GSM )
>>>                   then
>>>                     parseDeviceGSMData >>=
>>>                     ( \s -> return ( pl' { P.payloadData = pld {
>>> P.gsmData = Just s } } ) )
>>>                   else
>>>                     return pl' ) >>=
>>>      ( \pl' -> let pld = P.payloadData pl' in
>>>                 if testBit mdm ( fromEnum D.COT )
>>>                   then
>>>                     parseDeviceCOTData >>=
>>>                     ( \s -> return ( pl' { P.payloadData = pld {
>>> P.cotData = Just s } } ) )
>>>                   else
>>>                     return pl' ) >>=

Do notation is just syntax sugar for the above

do
  pl' <- .....
  pl' <- ....
  pl' <- ...

No additional variable invention required !


Andrew Butterfield
School of Computer Science & Statistics
Trinity College
Dublin 2, Ireland