List of partial functions

Partial functions in Prelude

Functions that aren't even partial

Function	Witness
error	error "x"
undefined	undefined

List functions

Function	Only partial for infinite lists	Witness
maximum	No	maximum []
minimum	No	minimum []
head	No	head []
tail	No	tail []
init	No	init []
last	No	last []
foldl	Yes	foldl (const (const ())) () [0..]
foldl'	Yes	foldl' (const (const ())) () [0..]
foldl1	No	foldl1 (const (const ())) []
foldl1'	No	foldl1' (const (const ())) []
foldr1	No	foldr1 (const (const ())) []
cycle	No	cycle []
!!	No	[] !! 0
filter	Yes	filter (const False) [0..]
dropWhile	Yes	dropWhile (const True) [0..]
length	Yes	length [0..]
sum	Yes	sum [0..]
product	Yes	product [0..]
reverse	Yes	reverse [0..]

Other

Function	Witness
read	read "x" :: Int
quot	1 `quot` 0
rem	1 `rem` 0
quotRem	1 `quotRem` 0
div	1 `div` 0
mod	1 `mod` 0
divMod	1 `divMod` 0
succ	succ ()
pred	pred ()
toEnum	toEnum 1 :: ()
(^)	1 ^ (-1)
fail	fail "x" :: Either () ()
... (todo)

Partial functions in other base libraries

Data.List

Function	Only partial for infinite lists	Witness
genericIndex	No	genericIndex [] 0
genericLength	Yes	genericLength [0..] :: Integer

Data.Map

Function	Witness
(!)	Map.empty ! ()

Data.Maybe

Function	Witness
fromJust	fromJust Nothing

Partial functions in other Haskell Platform packages

Function	Witness
... (todo)