Annotations

[Simon Peyton-Jones]

| My only worry is around the just implemented TH additions regarding
| annotations.  I don't clearly see what would happen if:
|   - a TH library exports a function that generates annotations when
| spliced.	
|   - and the user uses this function in a .hs file,
|   - without specifying the language extension.

But this is true for ANY language extension. If a TH library exports a function that generates (say) a type family declaration, and you splice that into a file, do you need -XTypeFamilies in the client file?   I think currently you do.  

So your point is a good one but it's orthogonal.

Simon

| -----Original Message-----
| From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of
| Gergely Risko
| Sent: 06 November 2013 11:57
| To: ghc-devs at haskell.org
| Cc: glasgow-haskell-users at haskell.org
| Subject: Re: Annotations
| 
| On Wed, 6 Nov 2013 10:55:09 +0000, Simon Peyton-Jones
| <simonpj at microsoft.com> writes:
| 
| > I’m inclined to add a language extension “Annotations”.
| >
| > · Without it {-# ANN … #-} pragmas are ignored as comments
| >
| > · With it, they are treated as annotations
| >
| > Do you agree?
| 
| I generally agree that this should be a language extension.
| 
| My only worry is around the just implemented TH additions regarding
| annotations.  I don't clearly see what would happen if:
|   - a TH library exports a function that generates annotations when
| spliced.	
|   - and the user uses this function in a .hs file,
|   - without specifying the language extension.
| 
| I'd it to work even in that case.
| 
| I guess the behavior in this corner case depends heavily on how this is
| actually implemented.  If e.g. the reader is the only component that
| checks if the language extension is turned on, then I imagine that the
| TH way of putting in the annotation into the AST would just work.
| 
| On the other hand if the reader recognizes the annotations either way
| and some component after TH splicing is checking for the language
| extension, then my use-case would blow up.
| 
| TH currently is lenient in cases like this.  E.g. if you know that a
| Name is exported from a module and you reference it directly, without
| importing it everything will just work.  I'd like to have the same
| behavior for annotations.
| 
| Thanks,
| Gergely
| 
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