[Haskell-cafe] TH not compiling when writing the code directly does

Michael Jones mike at proclivis.com
Thu Mar 12 13:15:09 UTC 2015


Oh I see. The items passed to the devName’ constructor must be constructors too.

I guess I did not think of that way. I thought of them as filling holes in constructor, thus values.

Too much OO in my past :-(

I’m slowly rebuilding those old neurons into something better.


On Mar 12, 2015, at 5:05 AM, Bertram Felgenhauer <bertram.felgenhauer at googlemail.com> wrote:

> Dear Michael,
> Michael Jones wrote:
>> I’m stuck getting a TH expansion to compile. When I take the generated
>> code and compile it directly, it is fine. But when expanding and
>> compiling, it fails.
>> The problem seems related to instanceD, where I provide the type as:
>> (appT (appT (conT devName') (varT $ mkName "Word8")) (varT $ mkName "BV”))
> [...]
>>    Illegal type variable name: ‘BV’
> Indeed BV is the name of a type *constructor*, not a type *variable*,
> so you need to use `conT` instead of `varT`:
> (appT (appT (conT devName') (conT $ mkName "Word8")) (conT $ mkName "BV”))
> HTH,
> Bertram
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