[Template-haskell] Question about local bindings

[Simon Peyton-Jones]

Check out Section 9.2 in the original TH paper.  What you are trying to
do is akin to 'genSwap' in that section.

In general f depends on the arguments to test2, and so must be converted
to code. The paper says this at greater length.

Simon

| -----Original Message-----
| From: template-haskell-bounces at haskell.org
[mailto:template-haskell-bounces at haskell.org] On
| Behalf Of Andy Gill
| Sent: 17 April 2006 05:57
| To: template-haskell at haskell.org
| Subject: [Template-haskell] Question about local bindings
| 
| Fellow Templaters,
| 
| Why does
| 
| test2 () = runQ [| foldr f z xs |]
| (f,z,xs) = undefined
| 
| compile fine, but
| 
| test2 () = runQ [| foldr f z xs |]
|     where (f,z,xs) = undefined
| 
| fail with this message:
| 
| ./Language/Haskell/ER/Equation.hs:108:25:
|      Can't splice the polymorphic local variable `f'
|      In the first argument of `foldr', namely `f'
|      In the first argument of `runQ', namely `[| foldr f z xs |]'
|      In the definition of `test2':
|          test2 ()
|                  = runQ [| foldr f z xs |]
|                  where
|                      (f, z, xs) = undefined
| 
| Andy Gill
| 
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