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A demonstration about how an improper call to an untraceable partial function cut off the call stack
import GHC.Stack
-- | a wrapper function to make "last" from base traceable
last' :: HasCallStack => [a] -> a
last' xs = case xs of [] -> error "abuse last"; _ -> last xs
-- | a untraceable partial function
foo :: [Int] -> Int
foo xs = last' xs + 1
-- | a untraceable partial function
-- , which looks like traceable, but it's call stack is cut off by "foo"
bar :: HasCallStack => [Int] -> Int
bar xs = foo xs
-- | an empty list
-- , which is also an improper input of "last'"
xs :: [Int]
xs = []
-- | the program is expected to print a call stack telling how "bar" is called
-- , but we can only know that "foo" called "last'" improperly from the printed call stack
main :: IO ()
main = print $ bar xs
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