Hi TP,
The reason that your initial example doesn't work is that Template Haskell
splices can be used in four places: expressions, types, patterns (I think), and
top-level declarations. The number in a fixity declaration is none of these.
It's not an expression because you must write a literal number. However, the
fixity declaration itself can be produced by a splice, and you've discovered
that way out.
About your first issue, I don't quite know what's going on there, either, I'm
afraid.
Richard
On Jun 29, 2013, at 9:03 PM, TP wrote:
> TP wrote:
>
>> 2/ If I define in a module:
>>
>> j = 3
>>
>> and then define in another module:
>>
>> -------------------
>> h x = $([|j|])
>> main = do
>> print $ h undefined
>> -------------------
>>
>> I obtain "3" as expected.
>>
>> However, I do not achieve to make this system work with an infix
>> declaration:
>>
>> infix $([| j |]) +
>>
>> I obtain:
>>
>> parse error on input `$('
>
> I don't know what happens exactly, but one way to get out of this problem is
> to write the complete top-level declaration with a splice, instead of only
> the fixity level:
>
> $(return $ [ InfixD (Fixity $([| j |]) InfixN) (mkName "+") ])
>
> Concerning my first question, I have not been able to understand what
> happens at this time. I continue to look at it.
>
> Thanks,
>
> TP
>
>
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