TH bug: Lift (a -> b) where

[Simon Peyton-Jones]

This isn't a bug, in fact.  TH certainly lets you write programs that,
when GHC runs them for you, will loop, and this is one of them.  

When you write

	instance Lift (a -> b) where
	  lift f = [| f |]

that is shorthand for

	instance Lift (a->b) where
	  lift f = lift f

and that gives the infinite loop. 

Simon

| -----Original Message-----
| From: glasgow-haskell-bugs-bounces at haskell.org
[mailto:glasgow-haskell-bugs-
| bounces at haskell.org] On Behalf Of Saswat Anand
| Sent: 19 May 2004 21:05
| To: glasgow-haskell-bugs at haskell.org
| Subject: TH bug: Lift (a -> b) where
| 
| Hello,
| 
| I dont know if it has been reported, this looks like a bug in TH. The
| program goes into infinite loop.
| 
| Saswat
| 
| -----------------------------
| instance Lift (a -> b) where
|  lift f = [| f |]
| 
| compile :: (a -> b) -> ExpQ
| compile p = lift p
| 
| printE :: ExpQ -> IO ()
| printE expQ = do exp <- unQ expQ
|                             putStrLn (show exp)
| 
| inc x = x + 1
| 
| main = printE (compile inc)
| -----------------------------
| 
| 
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