RE: Determine instance method from class method callsite

[Simon Peyton Jones via ghc-devs]

|  lookupInstEnv from the InstEnv module seemed to do it, but it seems to
|  look up the matching key from a set of instEnv keys and not anything
|  that contains the instance bindr. Not sure.

I couldn't understand this.  lookupInstEnv is probably what you want.  It 
returns a ClsInstLookupResult

type InstMatch = (ClsInst, [DFunInstType])

type ClsInstLookupResult
 = ( [InstMatch] -- Successful matches
   , [ClsInst]   -- These don't match but do unify
   , [InstMatch] )   -- Unsafe overlapped instances under Safe Haskell
 -- (see Note [Safe Haskell Overlapping Instances] in
 -- TcSimplify).

Inside the ClsInst of the InstMatches you'll find a DFunId, which is (I think) 
what you are after.

Simon

|  -Original Message-
|  From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of
|  Tillmann Vogt via ghc-devs
|  Sent: 19 October 2017 18:13
|  To: ghc-devs@haskell.org
|  Subject: Re: Determine instance method from class method callsite
|  
|  I have the same problem  with a compiler plugin that I am writing.
|  
|  In GHC Core I need to get from a dict-fun identifier (e.g.
|  $fMyClassDouble to the type class instance bindr (starting with $c).
|  
|  lookupInstEnv from the InstEnv module seemed to do it, but it seems to
|  look up the matching key from a set of instEnv keys and not anything
|  that contains the instance bindr. Not sure.
|  
|  Where is the dictionary lookup that gives me the bindr?
|  
|  What I did so far:
|  
|  evalExpr :: DynFlags -> ModGuts -> CoreExpr -> Var ->  CoreM NodeType
|  evalExpr dflags guts (Var iD) v = do
|  
| hsc_env <- getHscEnv
| eps <- liftIO (hscEPS hsc_env)
| let instEnvs = InstEnvs (eps_inst_env eps)
| (mg_inst_env guts)
| (mkModuleSet (dep_orphs (mg_deps guts)))
| let ty = tyConAppTyCon_maybe (idType iD)
| let cl = fromJust (tyConClass_maybe (fromJust ty))
| let tys = snd (splitTyConApp (idType iD))
| let (matches,_,_) | isDictId iD = lookupInstEnv False instEnvs cl
|  tys
|   | otherwise = ([],[],[])
|  
| let inst = map (nameStableString . varName . is_dfun . fst) matches
|  
| liftIO $ B.appendFile ("debug.txt") (B.pack (show inst))
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Re: Determine instance method from class method callsite

[Tillmann Vogt via ghc-devs]

I have the same problem  with a compiler plugin that I am writing.

In GHC Core I need to get from a dict-fun identifier (e.g. 
$fMyClassDouble to the type class instance bindr (starting with $c).


lookupInstEnv from the InstEnv module seemed to do it, but it seems to 
look up the matching key from a set of instEnv keys and not anything 
that contains the instance bindr. Not sure.


Where is the dictionary lookup that gives me the bindr?

What I did so far:

evalExpr :: DynFlags -> ModGuts -> CoreExpr -> Var ->  CoreM NodeType
evalExpr dflags guts (Var iD) v = do

  hsc_env <- getHscEnv
  eps <- liftIO (hscEPS hsc_env)
  let instEnvs = InstEnvs (eps_inst_env eps)
  (mg_inst_env guts)
  (mkModuleSet (dep_orphs (mg_deps guts)))
  let ty = tyConAppTyCon_maybe (idType iD)
  let cl = fromJust (tyConClass_maybe (fromJust ty))
  let tys = snd (splitTyConApp (idType iD))
  let (matches,_,_) | isDictId iD = lookupInstEnv False instEnvs cl tys
| otherwise = ([],[],[])

  let inst = map (nameStableString . varName . is_dfun . fst) matches

  liftIO $ B.appendFile ("debug.txt") (B.pack (show inst))
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Re: Determine instance method from class method callsite

[Robin Palotai]

About "Var" - that is just a Name with additional info, but happens in the
typechecked tree (according to API docs).

2017-10-05 18:00 GMT+02:00 Simon Peyton Jones <simo...@microsoft.com>:

> well the HsWrapper might have something much more complicated than a
> DFunId.  It might need to construct the dictionary for Eq [a] from the DFun
> for Eq [a] and a dictionary for Eq a.
>
>
>
> it would be easy to resolve the Var of the instance method.
>
> I don’t know what “the var of the instance method” is.
>
>
>
> I feel I’m missing the point.  maybe others can help?
>
>
>
> Simon
>
>
>
> *From:* Robin Palotai [mailto:palotai.ro...@gmail.com]
> *Sent:* 05 October 2017 11:17
> *To:* Simon Peyton Jones <simo...@microsoft.com>
> *Cc:* GHC developers <ghc-devs@haskell.org>; haskell <
> haskell-c...@haskell.org>
> *Subject:* Re: Determine instance method from class method callsite
>
>
>
> Hello Simon - I outlined the approach in https://github.com/google/
> haskell-indexer/issues/73
> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fgoogle%2Fhaskell-indexer%2Fissues%2F73=02%7C01%7Csimonpj%40microsoft.com%7C6798607dd45a4865d5ef08d50bda3727%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636427954212256346=HkxeXUYlbyGJnHu2%2BM17Z5aE7XXAZCWCnWwGLMV1%2BEQ%3D=0>
> .
> TLDR is
> 1) at callsite, indeed the HsWrapper needs to be analysed to get the
> instance DFunId
>
> 2) at instance declaration site, we need to again take note of the DFunId.
>
> It is slightly more complicated than I expected the API. I would have
> expected that from having the Var of a class method, and the  of
> the instance (here DFunId), it would be easy to resolve the Var of the
> instance method.
>
> But it seems there's no direct way, one has to build a lookup table from
> the instance methods' (DFunId + plain stringy method name), and look that
> up from the callsite.
>
> Or I might have missed a way to deconstruct / query a DFunId for the
> method Vars.
>
> I'll put augmenting the commentary on my mental TODO list :)
>
>
>
> 2017-10-05 11:58 GMT+02:00 Simon Peyton Jones <simo...@microsoft.com>:
>
> Did you get a reply?
>
>
>
> I’m not 100% certain of your question, but consider the
>
>
>
> bar = show 
>
> for some expression e.   In the input to the type type checker the syntax
> tree for the RHS will be something like
>
> HsApp (HsVar “show”) 
>
>
>
> (The “show” isn’t really a string, it’s the Name for the class method.)
>
>
>
> After typechecking the syntax tree is augmented (or “elaborated”) with
> type and dictionary application.  So in concrete form it might look like
>
> bar = show @Foo dShowFoo 
>
>
>
> Because show :: forall a. Show a => a -> String, so show is apply to the
> type of its argument, and then to the dictionary.
>
>
>
> In HsSyn this part is done with a HsWrapper See TcEvidence.HsWrapper.  The
> elaborated syntax tree look like
>
>
>
> HsApp (HsWrap  (HsVar “show”))
>
>   
>
>
>
> The  part expresses the type and dictionary application. In this
> case it’ll look like
>
> WpEvApp dShowFoo (WpTyApp Foo WpHole)
>
>
>
> See the notes with `HsWrapper` in TcEvidence.
>
>
>
> Does that help?
>
>
>
> It would be great to augment the https://ghc.haskell.org/trac/
> ghc/wiki/Commentary with this sort of info (insofar as it doesn’t have it
> already).  If you augment I can review.  Email is quickly lost.
>
>
>
> Simon
>
> *From:* ghc-devs [mailto:ghc-devs-boun...@haskell.org] *On Behalf Of *Robin
> Palotai
> *Sent:* 19 September 2017 06:39
> *To:* GHC developers <ghc-devs@haskell.org>; haskell <
> haskell-c...@haskell.org>
> *Subject:* Determine instance method from class method callsite
>
>
>
> Sorry, I messed up subject and mailing list. Copying to both list now
> after the mistake (wanted only ghc-devs for specificity).
>
>
>
> Thanks!
>
>
>
> 2017-09-19 7:36 GMT+02:00 Robin Palotai <palotai.ro...@gmail.com>:
>
> Hello GHC devs,
>
>
>
> Before inventing the wheel, want to check if there is a GHC API way to
> look up the (fully) resolved instance method from a class method.
>
>
>
> For example, given a code
>
>
>
> data Foo Int deriving Show
>
>
>
> bar = show (Foo 3)
>
>
>
> when inspecting the Typechecked AST for bar's show call, I would like to
> get to the Name / Id of 'show' of the 'Show' typeclass.
>
>
>
> I believe I 

RE: Determine instance method from class method callsite

[Simon Peyton Jones via ghc-devs]

well the HsWrapper might have something much more complicated than a DFunId.  
It might need to construct the dictionary for Eq [a] from the DFun for Eq [a] 
and a dictionary for Eq a.

it would be easy to resolve the Var of the instance method.
I don't know what "the var of the instance method" is.

I feel I'm missing the point.  maybe others can help?

Simon

From: Robin Palotai [mailto:palotai.ro...@gmail.com]
Sent: 05 October 2017 11:17
To: Simon Peyton Jones <simo...@microsoft.com>
Cc: GHC developers <ghc-devs@haskell.org>; haskell <haskell-c...@haskell.org>
Subject: Re: Determine instance method from class method callsite

Hello Simon - I outlined the approach in 
https://github.com/google/haskell-indexer/issues/73<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fgoogle%2Fhaskell-indexer%2Fissues%2F73=02%7C01%7Csimonpj%40microsoft.com%7C6798607dd45a4865d5ef08d50bda3727%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636427954212256346=HkxeXUYlbyGJnHu2%2BM17Z5aE7XXAZCWCnWwGLMV1%2BEQ%3D=0>.
TLDR is
1) at callsite, indeed the HsWrapper needs to be analysed to get the instance 
DFunId
2) at instance declaration site, we need to again take note of the DFunId.
It is slightly more complicated than I expected the API. I would have expected 
that from having the Var of a class method, and the  of the instance 
(here DFunId), it would be easy to resolve the Var of the instance method.
But it seems there's no direct way, one has to build a lookup table from the 
instance methods' (DFunId + plain stringy method name), and look that up from 
the callsite.
Or I might have missed a way to deconstruct / query a DFunId for the method 
Vars.
I'll put augmenting the commentary on my mental TODO list :)

2017-10-05 11:58 GMT+02:00 Simon Peyton Jones 
<simo...@microsoft.com<mailto:simo...@microsoft.com>>:
Did you get a reply?

I'm not 100% certain of your question, but consider the

bar = show 
for some expression e.   In the input to the type type checker the syntax tree 
for the RHS will be something like
HsApp (HsVar "show") 

(The "show" isn't really a string, it's the Name for the class method.)

After typechecking the syntax tree is augmented (or "elaborated") with type and 
dictionary application.  So in concrete form it might look like
bar = show @Foo dShowFoo 

Because show :: forall a. Show a => a -> String, so show is apply to the type 
of its argument, and then to the dictionary.

In HsSyn this part is done with a HsWrapper See TcEvidence.HsWrapper.  The 
elaborated syntax tree look like

HsApp (HsWrap  (HsVar "show"))
  

The  part expresses the type and dictionary application. In this case 
it'll look like
WpEvApp dShowFoo (WpTyApp Foo WpHole)

See the notes with `HsWrapper` in TcEvidence.

Does that help?

It would be great to augment the 
https://ghc.haskell.org/trac/ghc/wiki/Commentary with this sort of info 
(insofar as it doesn't have it already).  If you augment I can review.  Email 
is quickly lost.

Simon
From: ghc-devs 
[mailto:ghc-devs-boun...@haskell.org<mailto:ghc-devs-boun...@haskell.org>] On 
Behalf Of Robin Palotai
Sent: 19 September 2017 06:39
To: GHC developers <ghc-devs@haskell.org<mailto:ghc-devs@haskell.org>>; haskell 
<haskell-c...@haskell.org<mailto:haskell-c...@haskell.org>>
Subject: Determine instance method from class method callsite

Sorry, I messed up subject and mailing list. Copying to both list now after the 
mistake (wanted only ghc-devs for specificity).

Thanks!

2017-09-19 7:36 GMT+02:00 Robin Palotai 
<palotai.ro...@gmail.com<mailto:palotai.ro...@gmail.com>>:
Hello GHC devs,

Before inventing the wheel, want to check if there is a GHC API way to look up 
the (fully) resolved instance method from a class method.

For example, given a code

data Foo Int deriving Show

bar = show (Foo 3)

when inspecting the Typechecked AST for bar's show call, I would like to get to 
the Name / Id of 'show' of the 'Show' typeclass.

I believe I could use splitHsSigmaTy on the HsType of the function call to get 
the context, and then evaluate the HsWrapper somehow to find out what instance 
dictionary is applied to the class restriction in the context, and then look up 
the instance method from the dictionary..

Two questions:

1) Is there maybe functionality for this?

2) If not, is there any guarantee about the constraint order in the context, at 
the method call? So I could more easily determine which constraint's 
application to look for..

Any hints welcome && Thank you!
Robin


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Re: Determine instance method from class method callsite

[Robin Palotai]

Hello Simon - I outlined the approach in
https://github.com/google/haskell-indexer/issues/73.
TLDR is
1) at callsite, indeed the HsWrapper needs to be analysed to get the
instance DFunId
2) at instance declaration site, we need to again take note of the DFunId.

It is slightly more complicated than I expected the API. I would have
expected that from having the Var of a class method, and the  of
the instance (here DFunId), it would be easy to resolve the Var of the
instance method.

But it seems there's no direct way, one has to build a lookup table from
the instance methods' (DFunId + plain stringy method name), and look that
up from the callsite.

Or I might have missed a way to deconstruct / query a DFunId for the method
Vars.

I'll put augmenting the commentary on my mental TODO list :)

2017-10-05 11:58 GMT+02:00 Simon Peyton Jones <simo...@microsoft.com>:

> Did you get a reply?
>
>
>
> I’m not 100% certain of your question, but consider the
>
>
>
> bar = show 
>
> for some expression e.   In the input to the type type checker the syntax
> tree for the RHS will be something like
>
> HsApp (HsVar “show”) 
>
>
>
> (The “show” isn’t really a string, it’s the Name for the class method.)
>
>
>
> After typechecking the syntax tree is augmented (or “elaborated”) with
> type and dictionary application.  So in concrete form it might look like
>
> bar = show @Foo dShowFoo 
>
>
>
> Because show :: forall a. Show a => a -> String, so show is apply to the
> type of its argument, and then to the dictionary.
>
>
>
> In HsSyn this part is done with a HsWrapper See TcEvidence.HsWrapper.  The
> elaborated syntax tree look like
>
>
>
> HsApp (HsWrap  (HsVar “show”))
>
>   
>
>
>
> The  part expresses the type and dictionary application. In this
> case it’ll look like
>
> WpEvApp dShowFoo (WpTyApp Foo WpHole)
>
>
>
> See the notes with `HsWrapper` in TcEvidence.
>
>
>
> Does that help?
>
>
>
> It would be great to augment the https://ghc.haskell.org/trac/
> ghc/wiki/Commentary with this sort of info (insofar as it doesn’t have it
> already).  If you augment I can review.  Email is quickly lost.
>
>
>
> Simon
>
> *From:* ghc-devs [mailto:ghc-devs-boun...@haskell.org] *On Behalf Of *Robin
> Palotai
> *Sent:* 19 September 2017 06:39
> *To:* GHC developers <ghc-devs@haskell.org>; haskell <
> haskell-c...@haskell.org>
> *Subject:* Determine instance method from class method callsite
>
>
>
> Sorry, I messed up subject and mailing list. Copying to both list now
> after the mistake (wanted only ghc-devs for specificity).
>
>
>
> Thanks!
>
>
>
> 2017-09-19 7:36 GMT+02:00 Robin Palotai <palotai.ro...@gmail.com>:
>
> Hello GHC devs,
>
>
>
> Before inventing the wheel, want to check if there is a GHC API way to
> look up the (fully) resolved instance method from a class method.
>
>
>
> For example, given a code
>
>
>
> data Foo Int deriving Show
>
>
>
> bar = show (Foo 3)
>
>
>
> when inspecting the Typechecked AST for bar's show call, I would like to
> get to the Name / Id of 'show' of the 'Show' typeclass.
>
>
>
> I believe I could use splitHsSigmaTy on the HsType of the function call to
> get the context, and then evaluate the HsWrapper somehow to find out what
> instance dictionary is applied to the class restriction in the context, and
> then look up the instance method from the dictionary..
>
>
>
> Two questions:
>
>
>
> 1) Is there maybe functionality for this?
>
>
>
> 2) If not, is there any guarantee about the constraint order in the
> context, at the method call? So I could more easily determine which
> constraint's application to look for..
>
>
>
> Any hints welcome && Thank you!
>
> Robin
>
>
>
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RE: Determine instance method from class method callsite

[Simon Peyton Jones via ghc-devs]

Did you get a reply?

I’m not 100% certain of your question, but consider the

bar = show 
for some expression e.   In the input to the type type checker the syntax tree 
for the RHS will be something like
HsApp (HsVar “show”) 

(The “show” isn’t really a string, it’s the Name for the class method.)

After typechecking the syntax tree is augmented (or “elaborated”) with type and 
dictionary application.  So in concrete form it might look like
bar = show @Foo dShowFoo 

Because show :: forall a. Show a => a -> String, so show is apply to the type 
of its argument, and then to the dictionary.

In HsSyn this part is done with a HsWrapper See TcEvidence.HsWrapper.  The 
elaborated syntax tree look like

HsApp (HsWrap  (HsVar “show”))
  

The  part expresses the type and dictionary application. In this case 
it’ll look like
WpEvApp dShowFoo (WpTyApp Foo WpHole)

See the notes with `HsWrapper` in TcEvidence.

Does that help?

It would be great to augment the 
https://ghc.haskell.org/trac/ghc/wiki/Commentary with this sort of info 
(insofar as it doesn’t have it already).  If you augment I can review.  Email 
is quickly lost.

Simon
From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of Robin Palotai
Sent: 19 September 2017 06:39
To: GHC developers <ghc-devs@haskell.org>; haskell <haskell-c...@haskell.org>
Subject: Determine instance method from class method callsite

Sorry, I messed up subject and mailing list. Copying to both list now after the 
mistake (wanted only ghc-devs for specificity).

Thanks!

2017-09-19 7:36 GMT+02:00 Robin Palotai 
<palotai.ro...@gmail.com<mailto:palotai.ro...@gmail.com>>:
Hello GHC devs,

Before inventing the wheel, want to check if there is a GHC API way to look up 
the (fully) resolved instance method from a class method.

For example, given a code

data Foo Int deriving Show

bar = show (Foo 3)

when inspecting the Typechecked AST for bar's show call, I would like to get to 
the Name / Id of 'show' of the 'Show' typeclass.

I believe I could use splitHsSigmaTy on the HsType of the function call to get 
the context, and then evaluate the HsWrapper somehow to find out what instance 
dictionary is applied to the class restriction in the context, and then look up 
the instance method from the dictionary..

Two questions:

1) Is there maybe functionality for this?

2) If not, is there any guarantee about the constraint order in the context, at 
the method call? So I could more easily determine which constraint's 
application to look for..

Any hints welcome && Thank you!
Robin

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Re: Determine instance method from class method callsite

[Robin Palotai]

My conclusion so far: there's no royal way. One can get the instance
dictionary DFunId pretty easy, but then access to the Typechecked AST of
the instance declaration is really needed to find all the method bindings
$c... (that get applied when constructing the dictionary $d...).

2017-09-19 7:38 GMT+02:00 Robin Palotai :

> Sorry, I messed up subject and mailing list. Copying to both list now
> after the mistake (wanted only ghc-devs for specificity).
>
> Thanks!
>
> 2017-09-19 7:36 GMT+02:00 Robin Palotai :
>
>> Hello GHC devs,
>>
>> Before inventing the wheel, want to check if there is a GHC API way to
>> look up the (fully) resolved instance method from a class method.
>>
>> For example, given a code
>>
>> data Foo Int deriving Show
>>
>> bar = show (Foo 3)
>>
>> when inspecting the Typechecked AST for bar's show call, I would like to
>> get to the Name / Id of 'show' of the 'Show' typeclass.
>>
>> I believe I could use splitHsSigmaTy on the HsType of the function call
>> to get the context, and then evaluate the HsWrapper somehow to find out
>> what instance dictionary is applied to the class restriction in the
>> context, and then look up the instance method from the dictionary..
>>
>> Two questions:
>>
>> 1) Is there maybe functionality for this?
>>
>> 2) If not, is there any guarantee about the constraint order in the
>> context, at the method call? So I could more easily determine which
>> constraint's application to look for..
>>
>> Any hints welcome && Thank you!
>> Robin
>>
>
>
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Determine instance method from class method callsite

[Robin Palotai]

Sorry, I messed up subject and mailing list. Copying to both list now after
the mistake (wanted only ghc-devs for specificity).

Thanks!

2017-09-19 7:36 GMT+02:00 Robin Palotai :

> Hello GHC devs,
>
> Before inventing the wheel, want to check if there is a GHC API way to
> look up the (fully) resolved instance method from a class method.
>
> For example, given a code
>
> data Foo Int deriving Show
>
> bar = show (Foo 3)
>
> when inspecting the Typechecked AST for bar's show call, I would like to
> get to the Name / Id of 'show' of the 'Show' typeclass.
>
> I believe I could use splitHsSigmaTy on the HsType of the function call to
> get the context, and then evaluate the HsWrapper somehow to find out what
> instance dictionary is applied to the class restriction in the context, and
> then look up the instance method from the dictionary..
>
> Two questions:
>
> 1) Is there maybe functionality for this?
>
> 2) If not, is there any guarantee about the constraint order in the
> context, at the method call? So I could more easily determine which
> constraint's application to look for..
>
> Any hints welcome && Thank you!
> Robin
>
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