[Template-haskell] Reification of local names
lists at stefanheimann.net
Thu Jun 17 10:45:55 EDT 2004
I need to extract some type information from the syntax
tree. Therefore I need to reify non-global names. Take the following
module A where
logQ = runIO . putStrLn
stringOfInfo (ClassI _) = "ClassI"
stringOfInfo (ClassOpI name t _ _) = "ClassOpI " ++ show name ++ " :: " ++ show t
stringOfInfo (TyConI _) = "TyConI"
stringOfInfo (DataConI name t _ _) = "DataConI " ++ show name ++ " :: " ++ show t
stringOfInfo (VarI name t _ _) = "VarI " ++ show name ++ " :: " ++ show t
stringOfInfo (TyVarI name t) = "TyVarI " ++ show name ++ " = " ++ show t
foo :: Q Exp -> Q [Dec]
foo e' = do e <- e'
case e of
LetE _ (VarE name) -> do info <- reify name
logQ (stringOfInfo info)
module Main where
$(foo [| let f = \x -> x + 2
in f |])
main = return ()
What the example does is trying to reify 'f' in the expression
let f = \x -> x + 2
When I now compile the example, I get the following output:
$ ghc-cvs --make -fth B.hs
Chasing modules from: B.hs
Compiling A ( ./A.hs, ./A.o )
Compiling Main ( B.hs, B.o )
Loading package base ... linking ... done.
Loading package haskell98 ... linking ... done.
Loading package template-haskell ... linking ... done.
B.hs:1:0: tcLookupGlobal: `f' is not in scope
Exception when trying to run compile-time code:
Code: foo ([| let f = \ x -> ... in f |]
Exn: user error (IOEnv failure)
I am using the development snapshot ghc-6.3.20040612.
So my question is: Is it simply not possible to reify local
definitions, is it a bug or is it not yet implemented? If it is
possible in general to reify local definitions but just not
implemented at the moment, do you have any schedule on when an
implementation will be available?
Thanks for helping!
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