[Haskell-cafe] Generic functional references for free, now!

[Sterling Clover]

Recent discussions inspired me to cook up the attached, which through controlled abuse of various extensions gives functional references for all records deriving Data and Typeable for free, with no template haskell necessary. Composition is fully supported, as is "overloading" of standard record accessors. For the sake of preserving at least mild sanity, the (.) operator is not overloaded, and composition is instead provided via an overloaded `o`.

Cheers, and happy hacking,
Sterl.

Example usage:







*GenericFRef> set t1 23 testData


*GenericFRef> set (t'1 `o` t4) 23 testData


*GenericFRef> update (t2) (\x->x*x) testData


*GenericFRef> update (t'2 `o` t4) (\x->x*x) testData

For anyone that doesn't mind the absurdity of how this is implemented, it should be suitable for "drop in" use. For those that do mind the absurdity, it nonetheless serves as a proof-of-concept for how far Haskell's reflective capacities can be pushed. data Test = Test {t1 :: Int, t2 :: Int, t3 :: String, t4 :: InnerTest} deriving (Data, Typeable, Show) data InnerTest = InnerTest {t'1 :: Int, t'2 :: Int, t'3 :: String} deriving (Data, Typeable, Show) testData = Test {t1 = 1, t2 = 2, t3 = "foo", t4 = InnerTest {t'1 = 2, t'2 = 3, t'3 = "bar"}} Test {t1 = 23, t2 = 2, t3 = "foo", t4 = InnerTest {t'1 = 2, t'2 = 3, t'3 = "bar"}} Test {t1 = 1, t2 = 2, t3 = "foo", t4 = InnerTest {t'1 = 23, t'2 = 3, t'3 = "bar"}} Test {t1 = 1, t2 = 4, t3 = "foo", t4 = InnerTest {t'1 = 2, t'2 = 3, t'3 = "bar"}} Test {t1 = 1, t2 = 2, t3 = "foo", t4 = InnerTest {t'1 = 2, t'2 = 9, t'3 = "bar"}} p.s. I have a nagging sensation that somebody may have done this before, although I can't trace the source.

GenericFRef.hs
Description: Binary data

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