Extremely slow compilation of a program with multiply implicit parameters
Adding yet another ?tstX variable in this snippet slows down compilation by a factor of ten or so. Giving an explicit type annotation to tst1 makes compilation instant.
{-# LANGUAGE ImplicitParams #-}
data D = D Int deriving Show
slow_to_compile :: IO ()
slow_to_compile = do
tst1 <- return 1
let ?tst1 = tst1
let ?tst2 = tst1
let ?tst3 = tst1
let ?tst4 = tst1
let ?tst5 = tst1
let ?tst6 = tst1
let ?tst7 = tst1
print $ D ?tst1