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

16 Apr 2015

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On 16 Apr 2015, at 09:22, Tom Ellis  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 \
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On Wed, Apr 15, 2015 at 8:57 PM, Jeff  wrote:
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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