Sandbox::https://github.com/dhall-lang/dhall-haskell/pull/1119

ocharles · 2019-07-16T12:24:23Z

This allows Exprs to be lifted in template-haskell. This is useful to build a [dhall| ... |] quasiquoter

This allows Exprs to be lifted in template-haskell. This is useful to build a [dhall||] quasiquoter

Gabriella439 · 2019-07-16T16:18:41Z

 {-# LANGUAGE DeriveGeneric      #-}
+{-# LANGUAGE DeriveLift         #-}
 {-# LANGUAGE OverloadedStrings  #-}
+{-# LANGUAGE TemplateHaskell    #-}


Note that @vmchale at one point requested that Dhall not use TemplateHaskell or QuasiQuotes due to issues with cross-compilation. See: #89

@vmchale: Is this still a concern for you?

Actually, even if it were, we could guard this behind a cabal configure flag so that users can compile out Template Haskell support if necessary. But let's still confirm whether or not we even need to do so

It wouldn't be hard to remove it from this file.

Oh, if it's easy to do, then go ahead. The real issue here is that I just don't really understand what are the exact requirements for Dhall to be easy-to-cross-compile. For example, it's not clear to me if depending on th-lift-instances matters or not for the original use case @vmchale had in mind.

This can actually get away with just TemplateHaskellQuotes, which is cross-compilation friendly.

I've changed this to TemplateHaskellQuotes, I hadn't even heard of that extension!

sjakobi · 2019-07-17T22:22:25Z

Sorry for the merge conflicts, @ocharles! :/

ocharles · 2019-07-17T22:30:04Z

No problem! I have a little more work to do anyway, should be easy to fix up.

ocharles · 2019-07-18T16:51:01Z

Anyone got any ideas on the build failure? Is this Cabal messing up? It seems to be in the "Preprocessing" stage.

AndrasKovacs · 2019-07-18T16:54:10Z

FWIW, when I built your branch with stack just now, I got the same error, and added th-lift-instances-0.1.13@sha256:2852e468511805cb25d9e3923c9e91647d008ab4a764ec0921e5e40ff8a8e874 to stack.yaml. Then I got one more similar error about some th package, and added that to stack.yaml as well, and then it worked.

ocharles · 2019-07-18T16:55:35Z

Oh, that's a slightly different error but I do probably need to fix the stack.yml to use the newer versions of th-lift-instances and th-lift.

ocharles · 2019-07-19T21:04:37Z

I have a feeling that even though DeriveLift is supported on 7.10, this doesn't build on 7.10 because Cabal wasn't updated in time. haskell/cabal#2831 is the PR that teaches Cabal about the extension. @Gabriel439 what do you want to do about this?

Gabriella439 · 2019-07-19T22:59:32Z

@ocharles: I think the only option is to guard all of the Lift-related changes behind a Cabal macro. We currently have to support GHC 7.10 for Eta

quasicomputational · 2019-07-20T07:17:14Z

Cabal actually doesn't care - that list is only relevant for other-extensions / default-extensions, and even then it does the sensible thing of passing unknown values through to GHC, which is what really counts.

ocharles · 2019-07-20T11:52:17Z

@quasicomputational are you sure? Because this extension has existed since 7.4, yet the build is failing on 7.10

quasicomputational · 2019-07-21T08:12:03Z

GHC's manual says new in 8.0, so actually, yeah, this won't work without either conditionally exposing the Lift instance (which IMO is a bad idea) or defining it manually.

ocharles · 2019-07-21T11:47:55Z

Huh. This says since 7.2.1

ocharles · 2019-07-21T11:52:43Z

I guess this was a bug and the documentation has been fixed in HEAD?

sjakobi · 2019-07-21T11:55:19Z

I guess this was a bug and the documentation has been fixed in HEAD?

Right: https://gitlab.haskell.org/ghc/ghc/commit/1ad3c8245cc114c3f862633d027361700fba3e50

ocharles · 2019-07-21T12:36:22Z

Ok, I've taken a different approach using the default instance for Lift for any types that have a Data instance. All our types do, so this should work just as well.

Gabriella439 · 2019-07-21T14:45:59Z

@ocharles: It looks like we might need to replace TemplateHaskellQuotes with another extension for older GHC versions

ocharles · 2019-07-21T15:43:27Z

Yea I saw. Sorry, I'm traveling a lot this weekend so I'm just pushing commits out when I get a few minutes spare.

…

On Sun, 21 Jul 2019, 3:46 pm Gabriel Gonzalez, ***@***.***> wrote: @ocharles <https://github.com/ocharles>: It looks like we might need to replace TemplateHaskellQuotes with another extension for older GHC versions — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1119?email_source=notifications&email_token=AAAFDDTJGTKMPXVZVJIPHPDQARZCRA5CNFSM4IEALTVKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD2OFAAY#issuecomment-513560579>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAFDDU32OOZEMFWQLAJNHLQARZCRANCNFSM4IEALTVA> .

Gabriella439 · 2019-07-21T19:11:03Z

Thank you! 🙂

ocharles · 2019-07-21T19:44:05Z

Oh good, I finally got all CI systems happy!

Add instance Lift (Expr s a)

c2fd87a

This allows Exprs to be lifted in template-haskell. This is useful to build a [dhall||] quasiquoter

ocharles requested a review from Gabriella439 July 16, 2019 12:24

ocharles commented Jul 16, 2019

View reviewed changes

Comment thread dhall/dhall.cabal Resolved

Add instance Lift Src

30a6f3c

Gabriella439 reviewed Jul 16, 2019

View reviewed changes

ocharles added 7 commits July 18, 2019 11:50

Improve Lift X instance

1c8734b

Remove an unnecessary newline

69441ea

Replace -XTemplateHaskell with -XTemplateHaskellQuotes

0bfbc11

Drop -XDeriveLift

2c41500

Merge branch 'master' of https://github.com/dhall-lang/dhall-haskell

8ea7955

Override th-lift

fbd87aa

Override th-lift-instances

07094b3

Gabriella439 approved these changes Jul 19, 2019

View reviewed changes

Merge branch 'master' into master

957bf97

ocharles added 3 commits July 21, 2019 13:30

Don't use DeriveLift

8992e97

Merge branch 'master' of github.com:circuithub/dhall-haskell into lift

50cb809

Merge branch 'master' into master

cf6e9eb

Merge branch 'master' into master

77b8027

ocharles added 8 commits July 21, 2019 17:31

Use TemplateHaskell instead of TemplateHaskellQuotes

fce4dc7

Merge branch 'master' of github.com:circuithub/dhall-haskell into lift

9d7c770

Merge branch 'master' into master

ed9d5ed

Lift X

a6ae6ab

Update stack.yaml

8963f1b

Update stack.yaml

2f4f057

Fix stack-lts-12.yaml

ca9e749

Fix warnings

be53394

Gabriella439 merged commit d55bf8f into dhall-lang:master Jul 21, 2019

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ocharles commented Jul 16, 2019 •

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