Language level heads-up warnings

Simon Peyton-Jones simonpj at
Wed May 22 15:59:03 CEST 2013

I'm just saying that GHC has to be able to check while compiling one module, ie as now.  (It can see details of the things it imports, obviously, since it needs to know that to compile the module)

| -----Original Message-----
| From: David Luposchainsky [mailto:dluposchainsky at]
| Sent: 22 May 2013 14:54
| To: ghc-devs at
| Cc: Simon Peyton-Jones
| Subject: Re: Language level heads-up warnings
| On 2013-05-22 15:42, Simon Peyton-Jones wrote:
| > Yes, I think that if the libraries community thought it was
| > important, I (or indeed someone else) could add a couple of ad-hoc
| > warnings to GHC without much work. But you'd all need to be clear and
| > specific about what warnings were wanted, and they'd need to be easy
| > to check (ie no global program analysis).
| Simon,
| good to hear that it's worth thinking about.
| I'm not sure what exactly "no global program analysis" means here. Where
| would the boundaries of such warnings be? I could imagine problems if
| Applicative/Monad are defined in separate packages/modules (although
| that may be rare in practice).
| Greetings,
| David

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