Is there any good extension? Yes, it's in Control.Applicative. Belka wrote:
Hello, cafe visitors! :)
This is a double topic: 1. Can't find any good informative resource with descriptions of Haskell extensions. Could anybody please share good one if it exists? The only "good" one I found: http://hackage.haskell.org/trac/haskell-prime/wiki/HaskellExtensions But it's a bit too old and not that full... I undestand, that Haskell is kind of "boiling" language, in a sense of being neverending experiment. It develops all the time, extensions show up and drop out. So it's not that easy to support community with a fresh information about them. But on the other side, the property (of being "boiling" language) makes such information really important for community members... I think. :)
2. Consider situation: ----------------------------------- data SomeDataType = SomeDataType { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type} sdtField3 :: SomeDataType -> SDT_Field3Type sdtField3 sdt = f (sdtField1 sdt) (sdtField2 sdt) ----------------------------------- I induced recently, that it would be very comfortable if I could perform in a way like this: ----------------------------------- data SomeDataType = SomeDataType { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField3 :: SDT_Field2Type, sdtField3 = f sdtField1 sdtField2} ----------------------------------- The situation is not that rare, when dealing with nonprimitive data constructions. Moreover would be really comfortable to reduce ----------------------------------- data SomeDataType = SomeDataType_111 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type} | SomeDataType_222 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField5 :: SDT_Field5Type}
sdtField3 :: SomeDataType -> SDT_Field3Type sdtField3 sdt = case sdt of {SomeDataType_111 -> f (sdtField1 sdt) (sdtField2 sdt) ; SomeDataType_222 -> g (sdtField1 sdt) (sdtField2 sdt) (sdtField5 sdt)}
\/ \/ \/ \/ \/ \/ \/ \/ \/ \/
data SomeDataType = SomeDataType_111 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField3 :: SDT_Field3Type, sdtField3 = f sdtField1 sdtField2} | SomeDataType_222 { sdtField1 :: SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField5 :: SDT_Field5Type, sdtField3 :: SDT_Field3Type, sdtField3 = g sdtField1 sdtField2 sdtField5} -----------------------------------
Usable mechanics for realization would be: 1. Funtion similar to Data.Function.on (example: (*) `on` f = \x y -> f x * f y), but opposite - I called it under. t `under` f = \x y -> (x f) `t` (y f) 2. currying and uncurrying
Is there any such extension?
Belka