vvv

Commit Message Guidelines

Short (72 chars or less) summary

More detailed explanatory text. Wrap it to 72 characters. The blank
line separating the summary from the body is critical (unless you omit
the body entirely).

Write your commit message in the imperative: "Fix bug" and not "Fixed
bug" or "Fixes bug." This convention matches up with commit messages

vvv

import Data.Foldable (foldl')
import Debug.Trace (trace)

prnEqual :: (Eq a) => a -> a -> IO ()
prnEqual a b = if a == b then print "True" else print "False"

-- Note the absence of parentheses around `Eq a` and having exactly one `print`.
prnEqual' :: Eq a => a -> a -> IO ()
prnEqual' a b = print $ if a == b then "True" else "False"

vvv

{-- XXX Your definition of `checkChar` is okay, but the abstraction itself
 -- is very odd.  It is fine as an exercise of using "do" notation and
 -- `return`. In real code though explicit statements are both short and
 -- expressive (see lines 21-22).
checkChar :: IO Bool
checkChar = do
    c <- getChar
    return (c == 'y')
--}

vvv

listsum :: Num a => [a] -> a
listsum [] = 0
listsum (x:xs) = x + listsum xs

main :: IO ()
main = print $ listsum [1..5]