Basically I want to be able to make a few small changes to an already type checked AST and then query the type system, similar to what is possible with typed holes. So in my example I would like to move baz to the top level, and then invoke the type checker to get the required signature, without having to convert the partial result back to source and re-run the entire compilation. Alan On Sun, Jul 13, 2014 at 10:21 PM, Richard Eisenberg wrote:

Hello Alan,

It's not clear what you're asking for here. What's keeping you from "accessing the full power of the GHC type system"?

Richard

On Jul 9, 2014, at 4:35 PM, AlanKim Zimmerman wrote:

...

I have hit a problem in HaRe when lifting a declaration from e.g. a where clause of a function to the top level, where there is a type signature of any complexity.

e.g lifting 'baz' from function 'foo' below

-------------------------- foo a = baz where baz :: Int baz = xx 1 a

xx :: (Num t) => t -> t -> t xx p1 p2 = p1 + p2 --------------------------------------

becomes

--------------------------------------------- foo a = (baz xx a) where xx :: (Num t) => t -> t -> t xx p1 p2 = p1 + p2

-- baz:: (forall t. Num t => t -> t -> t) -> Int ->Int baz :: Num a => (a -> t1 -> t) -> t1 -> t baz xx a= xx 1 a -----------------------------------------------

For a very small subset this can be calculated easily, but for full generality it would be great to access the full power of the GHC type system.

So before diving in too deeply, I thought I would test the waters as to the feasibility of doing something like this. I was hoping that perhaps the effort at an external constraint solver might be making the interfacing slightly simpler.

Regards Alan

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I am working with HsSyn Name, resulting from calling.typecheckModule from the GHC API. This seems to give a workable balance between the ParsedSource which is lexically close to the original source but lacks grouping of related elements, and the TypecheckedSource which has had the type information reduced to the type checker output. I am not sure which of the two type signatures is the "right" one for a refactorer. The commented out one preserves that the original baz returns an Int, and splices in the xx signature, the uncommented one is as generated by GHC 7.6.3 when using the :i command in ghci. The API calls I would like to make would be something like reTypecheckModule :: GhcMonad http://www.haskell.org/ghc/docs/7.6.3/html/libraries/ghc-7.6.3/GHC.html#t:Gh... m => ParsedModule http://www.haskell.org/ghc/docs/7.6.3/html/libraries/ghc-7.6.3/GHC.html#t:Pa... -> m TypecheckedModule http://www.haskell.org/ghc/docs/7.6.3/html/libraries/ghc-7.6.3/GHC.html#t:Ty... which would take a modified ParsedModule (or RenamedSource, or whatever context is required), restore the original type checking environment, and redo the type checking phase. This would then allow a query something like the existing getInfo call to retrieve the inferred type. Alternatively, explicitly putting a typed hole in for the required signature as part of the changes going in to the call to reTypecheckModule and then processing the returned warnings would work just as well. But I suspect I should poke around in the internals a bit more to clarify my question by trying to actually do it. Alan On Sun, Jul 13, 2014 at 10:41 PM, Richard Eisenberg wrote:

Sorry -- I'm still not sure what you mean.

What AST are you working with? HsSyn RdrName? HsSyn Name? HsSyn Id? Core? And, in your original example, there is a commented-out type signature and then an uncommented-out one. Which are you trying to generate? Would the recent partial type signature work help you? (I don't think it's in HEAD yet.)

Perhaps give the type of a function in the GHC API that you would like to have...

Richard

On Jul 13, 2014, at 4:31 PM, AlanKim Zimmerman wrote:

Basically I want to be able to make a few small changes to an already type checked AST and then query the type system, similar to what is possible with typed holes.

So in my example I would like to move baz to the top level, and then invoke the type checker to get the required signature, without having to convert the partial result back to source and re-run the entire compilation.

Alan

On Sun, Jul 13, 2014 at 10:21 PM, Richard Eisenberg wrote:

...

Hello Alan,

It's not clear what you're asking for here. What's keeping you from "accessing the full power of the GHC type system"?

Richard

On Jul 9, 2014, at 4:35 PM, AlanKim Zimmerman wrote:

...

I have hit a problem in HaRe when lifting a declaration from e.g. a where clause of a function to the top level, where there is a type signature of any complexity.

e.g lifting 'baz' from function 'foo' below

-------------------------- foo a = baz where baz :: Int baz = xx 1 a

xx :: (Num t) => t -> t -> t xx p1 p2 = p1 + p2 --------------------------------------

becomes

--------------------------------------------- foo a = (baz xx a) where xx :: (Num t) => t -> t -> t xx p1 p2 = p1 + p2

-- baz:: (forall t. Num t => t -> t -> t) -> Int ->Int baz :: Num a => (a -> t1 -> t) -> t1 -> t baz xx a= xx 1 a -----------------------------------------------

For a very small subset this can be calculated easily, but for full generality it would be great to access the full power of the GHC type system.

So before diving in too deeply, I thought I would test the waters as to the feasibility of doing something like this. I was hoping that perhaps the effort at an external constraint solver might be making the interfacing slightly simpler.

Regards Alan

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