[GHC] #7828: RebindableSyntax and Arrow

[GHC]

#7828: RebindableSyntax and Arrow
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        Reporter:  AlessandroVermeulen        |            Owner:
            Type:  bug                        |  jstolarek
        Priority:  normal                     |           Status:  new
       Component:  Compiler (Type checker)    |        Milestone:  7.10.1
      Resolution:                             |          Version:  7.6.2
Operating System:  Unknown/Multiple           |         Keywords:
 Type of failure:  GHC rejects valid program  |     Architecture:
       Test Case:                             |  Unknown/Multiple
        Blocking:                             |       Difficulty:  Unknown
                                              |       Blocked By:
                                              |  Related Tickets:
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Comment (by jstolarek):

 > They are subsets of xs: xs1 is the variables used by c, while xs2 is the
 > variables used by ss but not bound in p. So the command 'c' gets local
 > environment xs1 and stack (). The translations of statements are arrows
 that
 > take an environment (here xs2) as input.

 That starts to make sense :-) As I understand `x1` and `x2` need not be
 disjoint - is that correct?

 I am yet to understand the rules for encoding the input parameters to the
 arrows.
 Is there a general rule that says when and in what order things are put on
 the stack?
 Is it the case that elements on the stack are never accessed and need to
 be popped
 if they are to be used?

 I know all of this could be deduced from the source code, but sadly this
 is not
 straightforward (at least for me).


 > I don't understand that question - I don't see a bind expression in the
 generated code.

 What I meant is that desugaring of arrow bind is completely different from
 monadic bind (which is desugared to `>>=`+lambda) so perhaps it deserves
 its own internal representation. But in fact this is what my prototype
 implements ie. it distingushes arrow and monadic bind.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7828#comment:22>
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