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{-# LANGUAGE ScopedTypeVariables, ExistentialQuantification, ApplicativeDo #-}
module Main where
import Control.Applicative
import Text.PrettyPrint
(a:b:c:d:e:f:g:h:_) = map (\c -> doc [c]) ['a'..]
-- a | b
test1 :: M ()
test1 = do
x1 <- a
x2 <- b
const (return ()) (x1,x2)
-- no parallelism
test2 :: M ()
test2 = do
x1 <- a
x2 <- const g x1
const (return ()) (x1,x2)
-- a | (b;g) | e
test3 :: M ()
test3 = do
x1 <- a
x2 <- b
x3 <- const g x2
x4 <- e
return () `const` (x1,x2,x3,x4)
-- (a ; (b | g)) | c
-- or
-- ((a | b); g) | c
test4 :: M ()
test4 = do
x1 <- a
x2 <- b
x3 <- const g x1
x4 <- c
return () `const` (x2,x3,x4)
-- (a | b | c); (g | h)
test5 :: M ()
test5 = do
x1 <- a
x2 <- b
x3 <- c
x4 <- const g x1
x5 <- const h x3
return () `const` (x3,x4,x5)
-- b/c in parallel, e/f in parallel
-- a; (b | (c; (d; (e | (f; g)))))
test6 :: M ()
test6 = do
x1 <- a
x2 <- const b x1
x3 <- const c x1
x4 <- const d x3
x5 <- const e x4
x6 <- const f x4
x7 <- const g x6
return () `const` (x1,x2,x3,x4,x5,x6,x7)
-- (a | b); (c | d)
test7 :: M ()
test7 = do
x1 <- a
x2 <- b
x3 <- const c x1
x4 <- const d x2
return () `const` (x3,x4)
-- a; (b | c | d)
--
-- alternative (but less good):
-- ((a;b) | c); d
test8 :: M ()
test8 = do
x1 <- a
x2 <- const b x1
x3 <- c
x4 <- const d x1
return () `const` (x2,x3,x4)
-- test that Lets don't get in the way
-- ((a | (b; c)) | d) | e
test9 :: M ()
test9 = do
x1 <- a
let x = doc "x" -- this shouldn't get in the way of grouping a/b
x2 <- b
x3 <- const c x2
x4 <- d
x5 <- e
let y = doc "y"
return ()
-- ((a | b) ; (c | d)) | e
test10 :: M ()
test10 = do
x1 <- a
x2 <- b
let z1 = (x1,x2)
x3 <- const c x1
let z2 = (x1,x2)
x4 <- const d z1
x5 <- e
return (const () (x3,x4,x5))
-- (a | b)
-- This demonstrated a bug in RnExpr.segments (#11612)
test11 :: M ()
test11 = do
x1 <- a
let x2 = x1
x3 <- b
let x4 = c
x5 = x4
return (const () (x1,x2,x3,x4))
main = mapM_ run
[ test1
, test2
, test3
, test4
, test5
, test6
, test7
, test8
, test9
, test10
, test11
]
-- Testing code, prints out the structure of a monad/applicative expression
newtype M a = M (Bool -> (Maybe Doc, a))
maybeParen True d = parens d
maybeParen _ d = d
run :: M a -> IO ()
run (M m) = print d where (Just d,_) = m False
instance Functor M where
fmap f m = m >>= return . f
instance Applicative M where
pure a = M $ \_ -> (Nothing, a)
M f <*> M a = M $ \p ->
let (Just d1, f') = f True
(Just d2, a') = a True
in
(Just (maybeParen p (d1 <+> char '|' <+> d2)), f' a')
instance Monad M where
return = pure
M m >>= k = M $ \p ->
let (d1, a) = m True
(d2, b) = case k a of M f -> f True
in
case (d1,d2) of
(Nothing,Nothing) -> (Nothing, b)
(Just d, Nothing) -> (Just d, b)
(Nothing, Just d) -> (Just d, b)
(Just d1, Just d2) -> (Just (maybeParen p (d1 <> semi <+> d2)), b)
doc :: String -> M ()
doc d = M $ \_ -> (Just (text d), ())
|
