How to turn LHExpr GhcPs into CoreExpr

Ben Gamari ben at
Thu Jan 23 12:53:48 UTC 2020

It is slightly disheartening that this relatively simple use-case requires reaching so deeply into the typechecker.

If there really exusts no easier interface then perhaps we should consider adopting your elaborateExpr as part of the GHC API.


- Ben 

On January 23, 2020 4:04:03 AM EST, Richard Eisenberg <rae at> wrote:
>I don't know the exact semantics of the interactive context, etc., but
>that looks plausible. It won't give the *wrong* answer. :)
>Thanks for sharing!
>> On Jan 23, 2020, at 4:52 AM, Yiyun Liu <liuyiyun at>
>> Thank you all for your help! It turns out that I was missing the
>constraint solving and zonking step by desugaring the result of
>tcInferSigma directly.
>> I have the implementation of the function here
>Not sure if it's 100% correct but at least it works for all the
>examples I can come up with so far.
>> - Yiyun
>> On 1/22/20 7:09 AM, Andreas Klebinger wrote:
>>> I tried this for fun a while ago and ran into the issue of needing
>to provide a type environment containing Prelude and so on.
>>> I gave up on that when some of the calls failed because I must have
>missed to set up some implicit state properly.
>>> I didn't have an actual use case (only curiosity) so I didn't look
>further into it. If you do find a way please let me know.
>>> I would also support adding any missing functions to GHC-the-library
>to make this possible if any turn out to be required.
>>> As an alternative you could also use the GHCi approach of using a
>fake Module. This would allow you to copy whatever GHCi is doing.
>>> But I expect that to be slower if you expect to process many such
>>> Richard Eisenberg schrieb am 22.01.2020 um 10:36:
>>>> You'll need to run the expression through the whole pipeline.
>>>> 1. Parsing
>>>> 2. Renaming
>>>> 3. Type-checking
>>>>   3a. Constraint generation
>>>>   3b. Constraint solving
>>>>   3c. Zonking
>>>> 4. Desugaring

Sent from my Android device with K-9 Mail. Please excuse my brevity.
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