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|
{-# LANGUAGE MultiWayIf #-}
module Main where
-- This is how we had to use multi-way if previously. Not indenting lines after
-- `|` was causing a parse error.
f1 x = if | even x
, x /= 0
-> True
| otherwise
-> False
-- This was previously causing a parse error, but actually it should work.
f2 x = if | even x
, x /= 0
-> True
| otherwise
-> False
-- If we don't generate {} in MultiWayIf we get a shift/reduce conflict here:
-- It's not clear which guards belong to `case` and which ones belong to `if`.
--
-- This test is to make sure we parse it correctly.
--
-- - If we shift, we get a non-exhaustive pattern error when argument is odd.
-- - If we reduce, we run the unreachable code when argument is odd.
f3 x = case x of
x' | even x' -> if | even x' -> 1 | otherwise -> error "should be unreachable"
| otherwise -> 3
-- Testing line breaks
f4 x = case x of
x' | even x' -> if
| even x' -> 1
| otherwise -> error "should be unreachable"
| otherwise -> 3
main :: IO ()
main = do
print (f3 1)
print (f3 2)
print (f4 1)
print (f4 2)
|
