[Hat] Program Compiles With GHC 6.6 but not Hat

[Thomas Davie]

Olaf,
   This brings up something that's been niggling me for a while.  Why  
can Hat not deal with defaulting?  Surely it could be handled by the  
first stage of hat-trans being inserting explicit type signatures  
based on the standard defaulting rules?

Bob

On 17 Nov 2006, at 20:43, Olaf Chitil wrote:

>
> This is caused by a limitation of Hat: Hat cannot handle defaulting  
> of numeric classes.
>
> Your Haskell program makes use of defaulting: The main function  
> could work with numbers of either type Int or Integer. The Haskell  
> defaulting rule says that in such a case it should choose Integer.
>
> To help Hat add a type annotation, e.g.
>
> main = do { print (takeodds [(1::Integer) ..7]); }
>
> To get a better error message, you could compile your original  
> program without -hat but with the additonal line
>
> default()
>
> which turns defaulting off and thus will yield an error message  
> about an ambiguous type variable referring to your original program.
>
> In real programs we have hardly ever come across uses of defaulting.
>
> Ciao,
> Olaf
>
>
> Aditya Siram wrote:
>
>> The following program compiles and runs on GHC 6.6 but fails to  
>> compile with the '-hat' option to hmake. The error message is:
>> **Begin Output**
>> hat-trans   HatTest.hs
>> Wrote Hat/HatTest.hs
>> ghc-6.6      -c -package hat -o Hat/HatTest.o Hat/HatTest.hs
>>
>> Hat/HatTest.hs:40:50:
>>    Ambiguous type variable `a' in the constraint:
>>      `Integral a'
>>        arising from use of `htakeodds' at Hat/HatTest.hs:40:50-58
>>    Probable fix: add a type signature that fixes these type  
>> variable(s)
>> **End Output**
>>
>> The program source is:
>>
>> import Prelude
>>
>> takeodds xs = [ x | x <- xs, (mod x 2) ==0]
>>
>> main = do { print (takeodds [1 ..7]); }
>>
>>
>> Thanks...
>> Deech
>>
>> _________________________________________________________________
>> Talk now to your Hotmail contacts with Windows Live Messenger.  
>> http://clk.atdmt.com/MSN/go/msnnkwme0020000001msn/direct/01/? 
>> href=http://get.live.com/messenger/overview
>>
>> _______________________________________________
>> Hat mailing list
>> Hat at haskell.org
>> http://www.haskell.org/mailman/listinfo/hat
>
>
> _______________________________________________
> Hat mailing list
> Hat at haskell.org
> http://www.haskell.org/mailman/listinfo/hat