Inserting a copy of a tuple into a list - list

Question

I'm still new to Haskell, my problem is I have issues with adding a modified copy of data type instance into the list of those instances (don't know if it's not synonym).
Data type name is Task, short Tas.
If a task is fulfilled I need to mark it as fulfilled and if it's repeatable, I need to set next date for it (while keeping it in fulfilled tasks).
My approach is to create a copy of that task, basing on it, but with different ID and date and insert it into the list.
remakeDate serves for returning increased date of Task.
fulfilledTaskInList :: [Task] -> Int -> Int -> [Task]
fulfilledTaskInList [ ] check_ID pk_task = []
fulfilledTaskInList (x:xs) check_ID pk_task = if getId x == check_ID then
if getRepeatT x /= 0 then let help = remakeTask x pk_task in
(setFulfill x):help:xs
else (setFulfill x):xs
else x: fulfilledTaskInList xs check_ID pk_task
remakeTask x pk_task = do
(in_year, in_month, in_day) <- remakeDate (getYear x) (getMonth x) (getDay x) (getRepeatT x)
(Tas {id_Task = pk_task , name = showName x , descr = showDescr x, day = in_day, month = in_month, year = in_year, hour = getHour x, minute = getMinute x, fulfill = 0, repeatT = getRepeatT x})
Error thrown by ghci:
Task.hs:94:18:
Couldn't match expected type `IO b0' with actual type `Task'
In a stmt of a 'do' block:
(Tas
{id_Task = pk_task, name = showName x, descr = showDescr x,
day = in_day, month = in_month, year = in_year, hour = getHour x,
minute = getMinute x, fulfill = 0, repeatT = getRepeatT x})
In the expression:
do { (in_year, in_month, in_day) <- remakeDate
(getYear x) (getMonth x) (getDay x)
(getRepeatT x);
(Tas
{id_Task = pk_task, name = showName x, descr = showDescr x,
day = in_day, month = in_month, year = in_year, hour = getHour x,
minute = getMinute x, fulfill = 0, repeatT = getRepeatT x}) }
In an equation for `remakeTask':
remakeTask x pk_task
= do { (in_year, in_month, in_day) <- remakeDate
(getYear x)
(getMonth x)
(getDay x)
(getRepeatT x);
(Tas
{id_Task = pk_task, name = showName x, descr = showDescr x,
day = in_day, month = in_month, year = in_year, hour = getH
our x,
minute = getMinute x, fulfill = 0, repeatT = getRepeatT x})
}
Failed, modules loaded: Functions.

Answer 1

The error is saying that the do block in remakeTask is producing a Task as its last statement, but because it's a do block, it should produce a monadic value, in this case IO something.
You can add a return similar to the one in plusYear to fix this specific problem. However in general you seem to be using IO when you don't really need to, so you might instead investigate removing the do blocks along with the use of return and IO.