In your code (elabRnExpr) you have
_ <- perhaps_disable_default_warnings $ simplifyInteractive residual You’ll notice that simplifyInteractive :: WantedConstraints -> TcM (Bag EvBind) So you are discarding the “evidence bindings” returned by simplifyInteractive. Those are precisely the bindings of the dictionaries (dictionaries are a form of “evidence”) that you need. Don’t discard them. Untested: ev_binds <- perhaps_disable_default_warnings $ simplifyInteractive residual let full_expr = mkHsDictLet (EvBinds ev_binds) tc_expr zonkTopLExpr full_expr Simon From: ghc-devs <[email protected]> On Behalf Of Yiyun Liu Sent: 03 February 2020 02:03 To: [email protected] Cc: James Parker <[email protected]> Subject: Free dictionary variables in elaborated core expressions Hi ghc-devs, About 10 days ago, I made a thread about defining a function called elaborateExpr which turns a string into a core expression<https://github.com/yiyunliu/ghc-elaboration-test/blob/8f362ad92dc6601b4cb7e4c76f0a42bc6b64480f/src/Main.hs#L55> within an interactive context. Now here's an unexpected behavior which I'm not sure how to deal with. Given the expression: (\x -> x + 1) :: Int -> Int I expect to get something that looks like: \ (x :: Int) -> + @ Int GHC.Num.$fNumInt x (GHC.Types.I# 1#) where GHC.Num.$fNumInt is the exported dictionary. What I actually get is something like this: \ (x :: Int) -> + @ Int $dNum_someuniqueid x (GHC.Types.I# 1#) where $dNum_someuniqueid is a free dictionary variable within the expression. I was confused by the occurrence of the free variable $dNum at first, but after running the command: "ghc -ddump-ds-preopt somefile.hs" to dump the core bindings, I found that the dictionary variables like $dNum_ are actually local variables defined at the top-level. My objective is to inline those top-level dictionary definitions into the core expression using let bindings, but it seems tricky since I'm doing everything within an interactive context. Calling getBindings<https://hackage.haskell.org/package/ghc-8.6.5/docs/GHC.html#v:getBindings> only gives me the expression I elaborated, but the dictionary is no where to be found. Interestingly, when I turn on flags such as "DeferTypedHoles" or "DeferOutOfScopeVariables", all the dictionaries are defined locally in let bindings. However, I can't replicate that behavior even with the flags on in the interactive context. How do I find the dictionaries? Thanks, - Yiyun
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