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{-# LANGUAGE OverloadedRecordDot #-}
{-# LANGUAGE NoRebindableSyntax #-}
module PprRecordDotSyntax2 where
data Foo = Foo { foo :: Bar } deriving (Show, Eq)
data Bar = Bar { bar :: Baz } deriving (Show, Eq)
data Baz = Baz { baz :: Quux } deriving (Show, Eq)
data Quux = Quux { quux :: Int } deriving (Show, Eq)
main = do
let a = Foo { foo = Bar{ bar = Baz { baz = Quux { quux = 42 } } } }
-- A "selector" is an expression like '(.a)' or '(.a.b)'.
putStrLn "-- selectors:"
print $ (.foo) a -- Bar { bar = Baz { baz = Quux { quux = 42 } } }
print $ (.foo.bar) a -- Baz { baz = Quux { quux = 42 } }
print $ (.foo.bar.baz) a -- Quux { quux = 42 }
print $ (.foo.bar.baz.quux) a -- 42
-- A "selection" is an expression like 'r.a' or '(f r).a.b'.
putStrLn "-- selections:"
print $ a.foo.bar.baz.quux -- 42
print $ a.foo.bar.baz -- Quux { quux = 42 }
print $ a.foo.bar -- Baz { baz = Quux { quux = 42 } }
print $ a.foo -- Bar { bar = Baz { baz = Quux { quux = 42 } } }
-- An "update" is an expression like 'r{ a.b = 12 }'.
--
-- We don't support these (in the case Rebindable Syntax is off) yet
-- (waiting on HasField support).
--
-- Regular updates are fine though!
print $ a{foo=(foo a){bar = (bar (foo a)){baz = (baz (bar (foo a))){quux = quux (baz (bar (foo a))) + 1}}}}
print $ a{foo=(a.foo){bar = (a.foo.bar){baz = (a.foo.bar.baz){quux = a.foo.bar.baz.quux + 1}}}}
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