Syntactic sugar for comonads

It could be useful to have this as extension.

More details: http://www.haskellforall.com/2013/02/you-could-have-invented-comonads.html chapter "Syntactic sugar for comonads"

method
    wa> expr1
    wb> expr2
    wc> expr3

= -- this desugars to:

   \wa ->
let wb =      extend (\this -> expr1) wa
    wc =      extend (\this -> expr2) wb
 in extract $ extend (\this -> expr3) wc

and

method
    expr1
    expr2
    expr3
=
   \_wa ->
let _wb =      extend (\this -> expr1) _wa
    _wc =      extend (\this -> expr2) _wb
in  extract  $ extend (\this -> expr3) _wc

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Trac field	Value
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Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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