Thanks Ross. I think I still don't understand the stk thing. What are

#7828: RebindableSyntax and Arrow ----------------------------------------------+---------------------------- 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: ----------------------------------------------+---------------------------- Comment (by ross): Replying to [comment:15 jstolarek]: the "anonymous inputs to the arrow"? Is that described in any of the arrow papers? They are command arguments, the arrow analogue of function arguments. But with arrows they have to be tupled up with the local environment as the input to the arrow. In the notation paper (section 3.2) these arguments are attached to the environment with a series of pairings, but before 7.8 I had to change the representation to fit with GHC's constraint-based typechecker. Now the environment and stack are separate tuples, combined in a pair.

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The simplifier reduces that to an identity using rules in Control.Arrow

How can I observe that? Using `-ddump-simpl` only shows that this huge expression is split into many smaller functions but it doesn't look like anything gets simplified. Using `-ddump-rules` and `-ddump-rule-rewrites` I see that some rules fire but none of them seems to optimize the above expression.

I used -O as well (this is with GHC 7.8.2). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7828#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler