Haskell - Overwriting parameters causes unexpected behaviours -

i wrote simple function

somefunc list elem =     list <- elem:elem:elem:list     return elem

now, when i'm using it, i'm getting output this

*main> somefunc [] 'a' "aaa"

despite fact, function has no practical use, why happen? why editing list have effect in elem? , how assign new value list avoiding situation?

note function de-sugared this:

somefunc :: [b] -> b -> [b] somefunc list elem = (elem:elem:elem:list) >>= \list -> return elem

now note list in \list -> return elem different input list pass function.

now see how monad instance list defined:

instance monad []       return x = [x]       xs >>= f = concat (map f xs)       fail _ = []

so, code translated form finally:

somefunc list elem = concat $ map (\list -> return elem) (elem:elem:elem:list)

now can understand why getting output ?

somefunc [] 'a' applied this:

concat $ map (\list -> return 'a') ('a':'a':'a':[]) concat $ [['a'],['a'],['a']] 'a':'a':'a':[] "aaa"

Remember