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How do I enforce run-time conditions on data in Haskell?

By : Michael Rivera
Date : October 18 2020, 08:10 PM
I wish did fix the issue. If you want to be formal about it it might be a good opportunity to use a smart constructor.
code :
module PSqList
    ( PSqList   -- constructor *not* exported
    , fromList

newtype PSqList a = PSqList [a]
    deriving (Functor, Foldable)

fromList :: [a] -> Maybe (PSqList a)
fromList xs
    | isPerfectSquare (length xs) = Just (PSqList xs)
    | otherwise = Nothing

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How to model entities to enforce a data models constraints at compile time?

By : Joe Rango
Date : March 29 2020, 07:55 AM
To fix the issue you can do I think that Code Contracts may be the only way to enforce something like this at compile time. Outside of compile time checks, writing unit tests to ensure the correct functionality is the next best thing!

Constant time Haskell List (Time Complexity? Haskell data types?) - Homework related

By : XenTeGio XenTeGio
Date : March 29 2020, 07:55 AM

MySQL: How to select max/min time data between specific time range with some conditions?

By : Chandra Mouli
Date : March 29 2020, 07:55 AM
With these it helps I have a set of data like this table: , This assumes sTime is a character string in the format you showed.
code :
SELECT name, date, IFNULL(intime, '') `In Time`, IFNULL(outtime, '') `Out Time`
    SELECT name, sdate AS date, 
        MIN(IF(SUBSTRING_INDEX(sTime, ' ', -2) BETWEEN '7:00:00 AM' AND '8:30:00 AM', 
                SUBSTRING_INDEX(SUBSTRING_INDEX(sTime, ' ', 2), ' ', -1), 
                NULL)) AS intime,
        MAX(IF(SUBSTRING_INDEX(sTime, ' ', -2) BETWEEN '4:00:00 PM' AND '5:15:00 PM', 
                SUBSTRING_INDEX(SUBSTRING_INDEX(sTime, ' ', 2), ' ', -1), 

                NULL)) AS outtime
    FROM YourTable
    GROUP BY name, sdate
    HAVING intime IS NOT NULL OR outtime IS NOT NULL
    ) AS x
ORDER BY intime IS NULL, intime, outtime

R - applying if conditions on time data to derive values before and after certain time point

By : George
Date : March 29 2020, 07:55 AM
I wish this helpful for you Maybe this could help, using lubridate library that is imho very intuitive. I've used EntryTime but you can apply it to any date column:
code :
# it's arleady as date, so you can do this
dats$time_if <- ifelse(hour(dats$EntryTime)<= 6,'a',
                       ifelse(hour(dats$EntryTime) >= 8,'b','c' ))

C++ enforce conditions on inherited classes

By : user3864932
Date : March 29 2020, 07:55 AM
seems to work fine You can force construction by making the no argument constructor private and having a public single int argument constructor in your base class. As long as the base class has some pure virtual methods, then your subclasses must call that constructor.
As for the operator==, try defining
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