TH has supported multi-parameter classes for a while... new in 6.4 is
support for fundeps.
Keean.
Benjamin Franksen wrote:
Two clarifications:
On Saturday 19 February 2005 22:33, Benjamin Franksen wrote:
instance RecordField R Label_field1 T1 where
getField (Rec x _) _ = x
putField (Rec _ y) _ v = Rec v x
s/Rec/R/
I wonder if something similar could be done with TH. The labels would need
to have a different name (e.g. l_field1, l_field2), so they don't collide
with their Haskell98 definitions, but otherwise everything should be as
above.
What I mean is: keep the record syntax and everything as it is now, but
additionally use TH in order derive the corresponding first class labels as
indicated above. The question is if a function 'generateLabels' can be
defined with TH. I remember darkly that TH is (or once was) restricted to
Haskell98, and so cannot be used to generate multi parameter class instances.
Ben
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