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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US">Conal<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US">Email is not good for this. I think it’d be more productive to have a Skype call, with both of use looking at GHC’s source code.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US">If you’d like to do that, do suggest a time.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D;mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif""> conal.elliott@gmail.com [mailto:conal.elliott@gmail.com]
<b>On Behalf Of </b>Conal Elliott<br>
<b>Sent:</b> 07 November 2013 18:15<br>
<b>To:</b> Simon Peyton-Jones<br>
<b>Cc:</b> Nicolas Frisby; ghc-devs@haskell.org<br>
<b>Subject:</b> Re: Finding & assembling class dictionaries from GHC plugins?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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On Wed, Nov 6, 2013 at 11:44 PM, Simon Peyton-Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Well, you are writing a function</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> reify :: CoreExpr -> HsExpr RdrName</span><o:p></o:p></p>
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Not exactly. I'm reifying CoreExpr directly to another CoreExpr. (The target CoreExpr calls into
<a href="https://github.com/conal/lambda-ccc/blob/master/src/LambdaCCC/Lambda.hs">
an API for GADT-typed lambda terms</a>. All works swimmingly as long as I'm able to avoid dictionary construction, but I'm no longer able to do so.) I haven't explored your suggestion of translating to HsExpr instead. Do you know of any plugins that work this
way? Do you really believe it would work out? For instance, I wouldn't know where to insert type annotations, and I'd have to back-translate names. I imagine there are other challenges I don't foresee.<br>
<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">It takes as its input a CoreExpr and produces as its output a reification of the input. I don’t
see why you need start by converting Core to HsExpr. Just write reify directly!</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">I wasn't suggesting converting a CoreExpr to an HsExpr. Rather, I was wondering out loud how I might get the type-checker's help to generate Core to find/assemble a Typeable dictionary for a given Core type
(since I'm starting with Core). One idea is translate the core type cty to an HsType hty, use hty in a very simple HsExpr like "Dict :: Dict hty" (where Dict is from Ed K's constraints package), use the typechecker to convert that simple HsExpr to a CoreExpr,
and then extract the dictionary-forming sub-CoreExpr. Or something simpler along the same lines.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Thanks for the help,<o:p></o:p></p>
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<p class="MsoNormal">-- Conal<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Simon</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">
<a href="mailto:conal.elliott@gmail.com" target="_blank">conal.elliott@gmail.com</a> [mailto:<a href="mailto:conal.elliott@gmail.com" target="_blank">conal.elliott@gmail.com</a>]
<b>On Behalf Of </b>Conal Elliott<br>
<b>Sent:</b> 07 November 2013 01:08</span><o:p></o:p></p>
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<b>To:</b> Simon Peyton-Jones<br>
<b>Cc:</b> Nicolas Frisby; <a href="mailto:ghc-devs@haskell.org" target="_blank">
ghc-devs@haskell.org</a><br>
<b>Subject:</b> Re: Finding & assembling class dictionaries from GHC plugins?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">Thanks for the suggestion. I hadn't considered backing up to an HsExpr. I guess we'd have to start by converting the Core Type to an HsType to form a type-annotated HsExpr. Am I on the
right track here?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">-- Conal<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">On Wed, Nov 6, 2013 at 5:59 AM, Simon Peyton-Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hmm. One route would be to build a HsExpr (rather than a CoreExpr) for the reification of your CoreExpr,
and stick that into the maw of the type checker. That would hand off all this dictionary construction to the type checker, which is designed for the purpose.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Simon</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">
<a href="mailto:conal.elliott@gmail.com" target="_blank">conal.elliott@gmail.com</a> [mailto:<a href="mailto:conal.elliott@gmail.com" target="_blank">conal.elliott@gmail.com</a>]
<b>On Behalf Of </b>Conal Elliott<br>
<b>Sent:</b> 05 November 2013 23:41<br>
<b>To:</b> Simon Peyton-Jones<br>
<b>Cc:</b> Nicolas Frisby; <a href="mailto:ghc-devs@haskell.org" target="_blank">
ghc-devs@haskell.org</a><br>
<b>Subject:</b> Re: Finding & assembling class dictionaries from GHC plugins?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">Hi Simon,<br>
<br>
Here's some context on what I'm after. I'll try to include enough to clarify what I'm after, without dragging you into unnecessary detail.<br>
<br>
I have a Core expression, which I'm systematically translating to a related Core expression. The second one reifies the first one, so that the generated code *evaluates* to a run-time (not compile/Core-time) representation akin to the original Core expression.
In this second (reified) representation, I need some run-time representation of types. I use Typeable constraints in my representation, and these constraints don't appear in the original Core representation. For instance, I have the following constructor for
function application in a GADT of lambda expressions:<br>
<br>
> (:^) :: (Typeable a, Typeable b) => E (a -> b) -> E a -> E b<br>
<br>
My reification plugin takes a Core application expression, recursively reifies the function and argument expressions, and makes an expression that applies (:^) to the two recursive results. However--and the point of this thread--I also need to come up with
Core expressions for the two Typeable dictionaries.<br>
<br>
So, to clarify my request, given a Core type representation t, I want to construct a Core expression that evaluates to the dictionary for Typeable t if one exists, or fail if there isn't one. Note that t is not necessarily an atomic type; it could instead be
something like [(Bool,Int -> String)].<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">I'm happy to Skype-chat if it'd help.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">Thanks, - Conal<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">On Tue, Nov 5, 2013 at 2:37 PM, Simon Peyton-Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
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<p style="margin-left:36.0pt">We just don't know how to start — ie how call the right functions from the type checker. Are there any resources explaining the relevant subset of the TcRnIf API?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">And I for my part don’t know where to start helping you! Conal wrote</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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I don't think I need to construct dictionaries for new Typeable instances. I only need to find and assemble *existing* Typeable instances into combinations like Typeable [(Bool,Int -> String)], and I don't know how to do so in a GHC plug-in<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">That’s exactly what the constraint solver does. (TcSimplify and friends.) But again I need more
context. </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">I gather you are talking to Pedro too? He knows a lot about this stuff.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Also there are a bunch of folk (Luite, Edsko) worked on the new front-end plugin stuff, and are much
more expert in it than me.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">We could have a skype call if that would help</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">S</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">
Nicolas Frisby [mailto:<a href="mailto:nicolas.frisby@gmail.com" target="_blank">nicolas.frisby@gmail.com</a>]
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<b>Sent:</b> 05 November 2013 14:36<br>
<b>To:</b> Simon Peyton-Jones<br>
<b>Cc:</b> <a href="mailto:ghc-devs@haskell.org" target="_blank">ghc-devs@haskell.org</a>; Conal Elliott<br>
<b>Subject:</b> RE: Finding & assembling class dictionaries from GHC plugins?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p>On Nov 5, 2013 3:14 AM, "Simon Peyton-Jones" <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> wrote:<o:p></o:p></p>
<p>><br>
> A core-level plug-in can’t generate fresh instances. There are some new plug-in hooks that fit earlier in the pipeline, which can. Maybe you can use that, and generate a data type decl with “deriving Typeable”?<o:p></o:p></p>
<p>We're willing to do some awkward shoehorning in HERMIT to make this work in limited circumstances. (Hopefully including Conal's.)<o:p></o:p></p>
<p>We just don't know how to start — ie how call the right functions from the type checker. Are there any resources explaining the relevant subset of the TcRnIf API?<o:p></o:p></p>
<p>Thanks.<o:p></o:p></p>
<p>> <br>
><br>
> From: ghc-devs [mailto:<a href="mailto:ghc-devs-bounces@haskell.org" target="_blank">ghc-devs-bounces@haskell.org</a>] On Behalf Of Conal Elliott<br>
> Sent: 04 November 2013 20:08<br>
> To: <a href="mailto:ghc-devs@haskell.org" target="_blank">ghc-devs@haskell.org</a><br>
> Subject: Finding & assembling class dictionaries from GHC plugins?<br>
><br>
> <br>
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> I'm working on a GHC plugin (for compiling Haskell to hardware), and I need to synthesize Typeable (and maybe other) class dictionaries for a wide range of types, including composite types (functions, pairs, lists, etc). Can it be done, and how? I think I'm
mainly looking for mechanics of finding existing class instances (however they're defined) and assembling them (for parametrized/composite dictionaries), rather than mechanisms specific to Typeable.<br>
><br>
> Thanks, -- Conal<br>
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><br>
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