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Document GHC-12219: static forms cannot be used in splices #494

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Document GHC-12219: static forms cannot be used in splices #494

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15 changes: 15 additions & 0 deletions message-index/messages/GHC-12219/index.md
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---
title: static forms cannot be used in splices
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Even while GHC itself starts the error message from lower case, I'd prefer to keep titles in title case.

Suggested change
title: static forms cannot be used in splices
title: Static forms cannot be used in splices

summary: Static forms are disallowed in splices
severity: error
introduced: 9.6.1
---

```
static.hs:7:45: error: [GHC-12219]
• static forms cannot be used in splices: static 'a'
• In the untyped splice: $(lift (show $ staticKey $ static 'a'))
```

GHC does not support using a static form in a splice, i.e. obtaining a reference
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I appreciate that it's tedious, but IMHO it's worth to provide readers with more context, especially when it comes to rare features of the language. Those who are already in the know what is a static form and what is a splice are not our target audience. For someone who encountered the error just by making a typo it would help to know which language extensions are involved and have a link to the GHC manual at ready.

I'd suggest to spell out "TemplateHaskell splices" in full, to make it unambiguous.

to a `StaticPtr` at compile time
10 changes: 10 additions & 0 deletions message-index/messages/GHC-12219/staticsplice/after/StaticSplice.hs
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{-# LANGUAGE StaticPointers #-}
{-# LANGUAGE TemplateHaskell #-}
module StaticSplice where

import GHC.StaticPtr
import Language.Haskell.TH.Syntax

main = print $([| show $ staticKey $ static 'a' |])


9 changes: 9 additions & 0 deletions message-index/messages/GHC-12219/staticsplice/before/StaticSplice.hs
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{-# LANGUAGE StaticPointers #-}
{-# LANGUAGE TemplateHaskell #-}

module StaticSplice where

import GHC.StaticPtr
import Language.Haskell.TH.Syntax

main = print =<< $(lift (show $ staticKey $ static 'a') )
9 changes: 9 additions & 0 deletions message-index/messages/GHC-12219/staticsplice/index.md
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---
title: GHC does not support defining static pointers in splices
---

You can't use a static forms in a splice - i.e. you can't obtain a `StaticPtr`
in code that runs at compile time.

Evaluating a quote that has a static form is not a problem, since this is code
that will be evaluated at run time.
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