[Template-haskell] types.

[Keean Schupke]

Last mail seemed to get lost (think I forgot to CC it to the list):

would this work with:

    $(something [d| f a = a + 1 |])

Such that I can reference the reified type of 'f' from inside 'something'.
'something' would be imported from another file. I am using ghc-6.4

    Keean.

Sean Seefried wrote:

>
> On 18/02/2005, at 8:11 PM, Keean Schupke wrote:
>
>> Is it possible to get at type information from TH? I am thinking of 
>> something
>> like the following:
>>
>> f a = a + 1
>>
>> {- ghc derives the type: f :: Integral a => a -> a -}
>>
>> Can I get at this derives type information? It would be very useful 
>> for the project I am working on... can I just reify the type of the 
>> function?
>>
>
> The answer to this question is a little tricky - it's yes with a few 
> caveats.  Firstly, the Q monad can be "run" in two contexts - within 
> the IO monad and with in the TcM monad of the GHC compiler.  You can't 
> you `reify' to get type information in the former context.
> Secondly, you can only reify the type of something that has been 
> imported from another module.  No go on the reifying something 
> declared within the module you're reifying in.
>
> I have two pieces of sample code that demonstrate the Q monad being 
> run within the TcM monad and within the IO monad.  The first one 
> works, the second doesn't. They are attached.
>
> These built in an old version of GHC 6.3. They should compile and run 
> in GHC 6.5 without *too* much difficulty although I haven't tested it.
>
> Cheers,
>
> Sean
>