Don’t know if asking for advice on the below code is too big an ask or not but thought I would ask. Even a tip from a quick glance or comment on one function would be appreciated.

This is a modified challenge from a book. The book uses semigroup and monoid and I would guess that is the best way but as a challenge to myself I wrote it without. The book also tended to pull values out of their types and put them back in. I read it is best to not do that so I tried to avoid.

```
{-
Find matching dates in 2 timeseries and show difference in values
Uses `Int` as proxy for date.
Usage:
Load into GHCi and then
> printIt (findDiffs file2 file3)
(11,201.6), (11,201.6) | 0.0
(12,201.5), (12,199.5) | 2.0
(13,201.5), (13,197.5) | 4.0
(14,203.5), (14,197.5) | 6.0
-}
{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
{-# HLINT ignore "Use newtype instead of data" #-}
import Data.List (intersectBy)
file1 :: [(Int,Double)]
file1 = [ (1,200.1), (2,199.5), (3,199.4)
, (4,198.9), (5,199.0), (6,200.2)
, (9,200.3),(10,201.2), (12, 202.9)]
file2 :: [(Int,Double)]
file2 = [(11,201.6), (12,201.5), (13, 201.5)
,(14, 203.5), (15, 204.9), (16, 207.1)
,(18, 210.5), (20, 208.8)]
file3 :: [(Int,Double)]
file3 = [(10, 201.2),(11, 201.6),(12, 199.5)
,(13, 197.5),(14, 197.5),(17, 210.5)
,(24, 215.1),(25, 218.7)]
file4 :: [(Int,Double)]
file4 = [(26, 219.8), (27,220.5),(28,223.8)
,(29, 222.8), (30, 223.8),(31, 221.7)
,(32, 222.3), (33, 220.8),(34, 219.4)
,(35, 220.1),(36, 220.6)]
data Time a = Time (Int,Double)
data Times a = Times [Time a]
fileToTimes :: [(Int,Double)] -> Times a
fileToTimes file = Times (map Time file)
instance Show (Time a) where
show (Time (t,v)) = "(" ++ show t ++ ", " ++ show v ++ ")"
instance Show (Times a) where
show (Times time) = concatMap (\(Time t) -> show t) time
compareDates :: Time a1 -> Time a2 -> Ordering
compareDates (Time t1) (Time t2)
| date1 > date2 = GT
| date1 < date2 = LT
| otherwise = EQ
where date1 = fst t1
date2 = fst t2
areDatesEqual :: Time a1 -> Time a2 -> Bool
areDatesEqual time1 time2 = compareDates time1 time2 == EQ
makeDiffs :: Times a -> Times a -> [(Time a, Time a)]
makeDiffs (Times time1) (Times time2) = zippedSets
where matchedDates = intersectBy areDatesEqual time1 time2
dates = map (\(Time t) -> fst t) matchedDates
set1 = filter (\(Time t) -> fst t `elem` dates) time1
set2 = filter (\(Time t) -> fst t `elem` dates) time2
zippedSets = zip set1 set2
-- Creates one row such as: "(1,2.5), (2,3.5) | -1.0"
makeLine :: Time a -> Time a -> String
makeLine (Time time1) (Time time2) = strFinal
where strTime1 = show time1
strTime2 = show time2
diff = snd time1 - snd time2
strFinal = concat [strTime1, ", ", strTime2, " | ", show diff, "\n"]
printIt :: [String] -> IO ()
printIt x = putStrLn (concat x)
findDiffs :: [(Int, Double)] -> [(Int, Double)] -> [String]
findDiffs f1 f2 = lines
where series1 = fileToTimes f1
series2 = fileToTimes f2
diffs = makeDiffs series1 series2
lines = map (\diff -> makeLine (fst diff) (snd diff)) diffs
```