- February 8th, 2018: We have maybe :: b -> (a -> b) -> Maybe a -> b. But we don't have list? Or do we? Define list:

list :: b -> ([a] -> b) -> [a] -> b

list nullanswer flist lst = undefined - BONUS: Both Maybe a and [a] are binary types, ... so is MonadPlus:

Maybe a = Nothing | Just a

List a = Cons a (List a) | Nil

MonadPlus m => mzero | m a `mplus` m a

Is there some generalization that maybe and list are functions of? What is that generalization? - February 6th, 2018:

You have f :: a -> [b] -> [c]

But instead of just one a you have [a]

Define g :: [a] -> [b] -> [c]

in terms of f - Daniel @leptonyu g as bs = foldl (\xs a -> f a bs ++ xs) [] as
- ptdr_bot @m0rth0n g as bs = flip f bs =<< as
- Victoria C @ToriconPrime g as bs = concat $ fmap ($ bs) (fmap f as)
- matt @themattchan g = flip $ concatMap . flip f
- Nicoλas @BeRewt g = flip (flip (>>=) . flip f) Or: g as bs = as >>= flip f bs
- Sangeet Kar @sangeet_kar g = foldMap f

# Typed Logic

Incorporates strong typing over predicate logic programming, and, conversely, incorporates predicate logic programming into strongly typed functional languages. The style of predicate logic is from Prolog; the strongly typed functional language is Haskell.

## Friday, April 13, 2018

### February 2018 1 Liner 1HaskellADay Problems and Solutions

## Monday, April 2, 2018

### March 2018 1HaskellADay problems and solutions

- March 14th, 2018: Wednesday #haskell problem I am thinking about sumaSumasCuadradosDivisores from the Haskell community via @Jose_A_Alonso
- March 12th, 2018: Monday's #haskell problem is Improving Tarski's logic language with curried functions.
- March 8th, 2018: For Thursday's #haskell problem, thanks to @wtfunctional, we'll play with Other People's Code! ... and Mandelbrot sets.
- March 6th, 2018: Tuesday's #haskell exercise asks the eternal question: "Are you my mom?"... and also looks at curried functions in a logic framework... which is nice. Last Tuesday's #haskell solution ended in pathos: I know 'momOf', but I cannot answer, 'are you my mom?' Can you not feel the sads?
- March 5th, 2018: Monday's #haskell problem is a little "Introduction to Logic" by Tarski to start our week of right. I went a little 'forall' in the #haskell solution today. Sorry. #notsorry

## Thursday, March 1, 2018

### February 2018 1HaskellADay problems and solutions

- February 28th, 2018: Wednesday's #haskell problem: (sung:) Ya know that I love Casey's Mom! (guitar wails) Wednesday's #haskell solution we solve with LOGIC PROGRAMMING! ... IN HASKELL! YES!
- February 27th, 2018: Tuesday's #haskell problem: A job scheduling problem, posed by Mensa, answered by Haskell. Tuesday's #haskell solution is this lcm/scan-like function, because "... the work is never done."
- February 22nd, 2018: Thursday's #haskell problem is counting in Haskell IN YOUR NATIVE LANGUAGE!
- February 21st, 2018: Wednesday's #haskell problem is sorting lists and making list-o-lists from lists, via P99 and random.org because my love-affair with #Prolog. *ahem* (pure) Prolog. Wednesday's #haskell solution: lsort and lfsort, provided to you by sortOn and by @bazzargh and @xgrommx
- February 20th, 2018: Tuesday's #haskell problem: More fun with elements in a list! Whee! Tuesday's #haskell solution: the monad-y approach, with alternatives by @xgrommx @bazzargh @johannesweiss
- February 19th, 2018: Monday's #haskell exercise is from @fermatslibrary: permutable primes. Monday's #haskell solution: Primes. Permutable. ... #PWND!
- February 16th, 2018: For Friday's #haskell problem P99 Prolog problem 33, coprime numbers with an assist by random.org. Friday's #haskell solution is coprimes: as easy as you please!
- February 15th, 2018: Thursday's #haskell problem is the greatest common denominator via P99 Prolog problem set. For today's #haskell solution I'VE JUST (re)INVENTED GCD! KNEEL BEFORE ZOD!
- February 14th, 2018: For Wednesday's #haskell problem: "I'm thinking of a word that has the letter 'V' ..." Happy Valentine's Day ... as an anagram! Today's #haskell solution was defined with ALACRITY! YUS!
- February 13th, 2018: Tuesday's #haskell problem: we have unicode, and we could parse that as Text, but why do that when they want plain, old ASCII? ... why, indeed! Removing non-ASCII characters from documents is one approach to parsing them...
- February 12th, 2018: A little CSV to JSON work via #haskell today. Monday's #haskell solution: 🎵 You say CSV, I say JSON. Let's call the whole thing off! 🎵
- February 9th, 2018: Logs get stale, quickly! Let's archive old log entries for Friday's #haskell problem... so quickly, in fact, that the Friday's #haskell solution archived 270k+ rows of log entries!
- February 7th, 2018: So, we will update articles in our PostgreSQL data store, but what happens when your codec is LATIN1 and you need to store the article as UTF8? Wednesday's #haskell problem. Wednesday's #haskell solution: TFW the exercise is an update function, but the solution goes whole-hog! smh 🙄
- February 6th, 2018: Tuesday's #haskell problem is timestamping packets and associating articles with the packets that downloaded them. Tuesday's #haskell solution: associating the articles we uploaded TODAY with the packet we uploaded TODAY!
- February 5th, 2018: On #SuperBowlSunday I release Monday's #haskell problem which is to timestamp log entries, because that's what we live for. Today's #haskell solution was a stunning victory by the Philadelphia Eagles ... no, ... wait: it was log entries, timestamped. There. #nailedit

- February 2nd, 2018: We've downloaded a the most recent set of articles from a REST endpoint; now we have to exclude Associated Press articles from our local paper's set. Friday's #haskell problem. Today's #haskell solution filters out Associated Press articles from out downloaded article-set.
- February 1st, 2018: Thursday's #haskell problem is from a picture posted from @fermatslibrary: anagrams as prime-multiples. Teacher: Class the following words are all English words: "Elaps lapse Lepas Pales salep saple sepal slape spale speal" Class: ... <<- a="" haskell="" href="https://3.bp.blogspot.com/-XHCUGvp7QhE/WnM0upUr8xI/AAAAAAAACCU/wUk6_uprpi4kqC2VZbHzlgs7XJHC3mP1gCLcBGAs/s1600/anagram-by-primes.jpg" imageanchor="1" no="" s="" solution.="" style="color: #7d181e; margin-left: 1em; margin-right: 1em; text-decoration: none;" words.="" yesterday="">

## Tuesday, February 6, 2018

### January 2018 1Liner 1HaskellADay problems and solutions

- January 8th, 2018: from Nicoλas @BeRewt

A small @1HaskellADay, old-school. Define foo:

> foo 3 [1..5]

[([1,2,3], 4), ([2,3,4], 5)]

> foo 2 [1..4]

[([1,2], 3), ([2,3], 4)]

> foo 2 [1..20]

[([1,2],3), ([2,3],4), ..., ([18,19],20)]

> foo 20 [1..2]

[] - Demiurge With a Teletype @mrkgrnao

foo n

= tails

# filter (length # (> n))

# map (splitAt n # second head)

(#) = flip (.) - Andreas Källberg @Anka213

I haven't tested it, but this should work:

foo n xs = [ (hd,x) | (hd , x:_) <- n="" splitat=""> tails xs ] - <- n="" splitat="">Nicoλas @BeRewt foo n = zip <$> fmap (take n) . tails <*> drop n
- January 5th, 2018: You have the following DAG-paths:

a -> b -> c -> e

a -> b -> d -> e

q -> r -> s

w -> x

y -> z

and many more.

From a path, provide a bi-directional encoding* given maximum graph depth is, say, 7, max number of roots is, say, 10, and max number of nodes is, say, 1000. - *bi-directional encoding of a graph path:

DAG path -> enc is unique for an unique DAG path

enc -> DAG path yields the same DAG path that created the unique enc.

*DAG: "Directed, acyclic graph." - January 5th, 2018: given s :: Ord k => a -> (k,[v])

define f using s

f :: Ord k => [a] -> Map k [v]

with no duplicate k in [a] - Christian Bay @the_greenbourne f = foldr (\e acc -> uncurry M.insert (s e) acc) M.empty
- me: you can curry away the acc variable easily
- Christian Bay @the_greenbourne You're right :)

f = foldr (uncurry M.insert . s) M.empty - Bazzargh @bazzargh fromList.(map s) ?
- me: Yuppers

## Wednesday, January 31, 2018

### January 2018 1HaskellADay Problems and Solutions

- January 30th, 2018: For Tuesday's #haskell problem we look at triaging articles downloaded from a REST endpoint against our PostgreSQL database. Who knew putting things into three bins could be so much fun? Today's #haskell solution triages work for us.
- January 29th, 2018: Monday's #haskell problem is to fetch when the last set of articles were stored; two approaches. Monday's #haskell solution: two approaches to extract 'last entry' from the database, wanted; two approaches to extract 'last entry' from the database, GOT!
- January 26th, 2018: Friday's #haskell problem is to pull a week's worth of data from a REST endpoint when we don't know
*a priori*how many calls we have to make. Friday's #haskell solution fetches then reads/parses blocks of articles from a REST endpoint. - January 24th, 2018: Wednesday's #haskell problem is solving three more #Prolog-y list problems from P99: pack / encode / decode. It's great when #haskell has grouping / 'un'grouping functions in the library already.
- January 23rd, 2018: Tuesday's #haskell problem: groups and grouper ... I like grouper blackened, please! Solving today's #haskell problem with Qubits?!? Nah, not really, but that would be cool if we did!
- January 22nd, 2018: Monday's #haskell problem is a problem from P99: problem P21, list insertion. Monday's #haskell solution is inserting an element into a list, PROLOG-STYLE!
- January 18th, 2018: The whole enchilada! Today's #haskell problem ties it all together to make an ETL. Today's #haskell solution defines etl: Looping over calls to the REST endpoint then database insertions.
- January 17th, 2018: For today's #haskell problem we use PostgreSQL data store and Haskell to pick up where we left off on an application run. Today's #haskell solution: the audit log has what our program last did, so now we know what we'll work on next!
- January 16th, 2018: Where did yesterday's Haskell problem go? Here it is! Today's #haskell problem: read a packet from a REST endpoint. Today's #haskell solution accesses a REST endpoint with a set timeout and with the default timeout.
- January 15th, 2018: "Logging? Why do we have to log stuff?" Enterprise applications require audit trails. Today's #haskell problem provides one. What did your Haskell app do and when? Today's #haskell solution: an audit log.
- January 11th, 2018: Thursday's #haskell problem: pulling SQL lookup tables into Haskell. Thursday's #haskell solution: with the help of IxValues we extract lookup table values from SQL into Haskell Maps.
- January 10th, 2018: Wednesday's #haskell exercise is to store the packet information into the PostgreSQL database as a part of auditing the ETL process. Wednesday's #haskell solution stores the packets that wrap article sets then logs our results.
- January 9th, 2018: Tuesday's #haskell problem we are logging log messages to the log data table. YES! Tuesday's #haskell solution: logging in the style of log4j.
- January 8th, 2018: Monday's #haskell problem: once more into the breach, and thoughts on generalization – storing unique newspaper article sections in PostgreSQL. We store article section information, then we build a function that stores ANYTHING! ... and washes windows, TOO! *

*YMMV additionaltermsandconditionsmayapplydependingonyourregion - January 5th, 2018: Friday's #haskell problem takes a break from SQL Databases and Haskell and does something completely different: data schemes and Haskell. AHA! Friday's #haskell solution is a graph-view of the sections for a sample of 100 articles.
- January 4th, 2018: Thursday's #haskell problem looks at storing in PostgreSQL authors of periodic articles uniquely identified by uuid. Thursday #haskell solution uses etl function with generators to store parsed authors in PostgreSQL database.

- January 3rd, 2018: Wednesday's #haskell problem is in honor of Baron Munchausen and his fantastic adventures!
- January 2nd, 2018: WELCOME TO THE NEW YEAR, HASKELLERS!

Tuesday's #haskell problem leverages keywords-as-subjects and makes storing article keywords into PostgreSQL easier... we hope. Tuesday's #haskell solution Incorporates prior work with memoizing tables and subjects with results.

## Friday, January 5, 2018

### December 2017 1HaskellADay 1Liners problems and solutions

- December 29th, 2017:

given f :: Monad m => n -> a -> m (Maybe b)

define g :: Monad m => n -> a -> m (a, Maybe b)

using f and ... arrows? Kleisli category? - Bazzargh @bazzargh (\n a->liftM ((,) a) (f n a)) ... according to pointfree.io, that's `liftM2 fmap (,) . f` but I can't pretend to get the transformation
- December 29th, 2017:

given f :: a -> b

define g :: [a] -> [Maybe c] -> [(b, c)]

>>> g [1,2,3] [Just 7, Nothing, Just 10]

[("1",7),("3",10)]

when f = show - matt @themattchan

g = catMaybes ... zipWith (fmap . (,) . f)

where (...) = (.).(.) - garrison @GarrisonLJ g a b = map (f.id***fromJust) . filter (isJust . snd) $ zip a b
- TJ Takei @karoyakani g = (catMaybes .) . zipWith ((<$>) . (,) . f)
- December 29th, 2017: define f :: [(a,b)] -> ([a], [b])
- Андреев Кирилл @nonaem00 and matt @themattchan unzip
- Victoria C @ToriconPrime f = fmap fst &&& fmap snd
- (in a vacuum, a more general type signature would be inferred, but the compiler limits itself as instruct)

## Tuesday, January 2, 2018

### December 2017 1HaskellADay problems and solutions

- December 29th, 2017: In Friday's #haskell problem we leave 2017 with a filter and a BANG! ... BANG! Today's #haskell solution we weave logging into the ETL article upload process.
- December 28th, 2017: Thursday's #haskell problem is late AND a quicky: fetch a row of JSON from the database and pretty-print it. Thursday's #haskell solution had me leap from the bath tub and shout EUREKA! as I saw the issue in the JSON.
- December 27th, 2017: In Wednesday's #haskell problem we learn that when you parse dates for your articles, you don't need to carbon-date it anymore. In the solution to yesterday's #haskell problem, we encounter and report some parsing issues around optionality.
- December 26th, 2017: Tuesday's #haskell problem: scan an article archive, store an article archive; databases are neat that way. Today's #haskell solution: storing articles-as-JSON into a PostgreSQL database? No problem!
- December 22nd, 2017: Friday's #haskell exercise we do our first bit of parsing with the help of tagsoup. Okay, this #haskell Aeson / TagSoup stuff is awesome for parsing JSON / HTML stuff.
- December 20th, 2017: Wednesday's #haskell exercise. We take a large-ish JSON article archive, scan it, and spit out* a smaller-...ish JSON article archive. *'spit out' is a technical term. Today's #haskell solution provides a subset of the JSON article archive printed prettily.
- December 18th, 2017: Monday's #haskell problem: Friday you submitted an oembed request for goats, today you create a JSON oembed response service. Today's #haskell solution brings you a goat oembed service, serve with PHP.
- December 15th, 2017: Today we build a goat oembed request. I kid you not! geddit? GEDDIT? Today's #haskell solution: OEmbed Goats requests, want? OEmbed Goats requests, GOT!
- December 14th, 2017: Thursday's #haskell problem we sing 🎵 ... EVERYBODY'S WORKIN' FOR THE WEEKEND! 🎶 So, 18 composeable dates on the weekends. I'm freeing up my calendar, then!
- December 13th, 2017: Wednesday's #haskell problem is a hot date! WOOT! Today's #haskell solution has 66 composable dates in 2017. Cool!
- December 12th, 2017: Tuesday's #haskell problem is batching a SQL queryinstead of making multiple queries. It is so much faster! Today's #haskell solution has another LEFT JOIN in the SQL query to consolidate data gathering.
- December 11th, 2017: Monday's #haskell problem is computing and storing exponential distribution values. The exponential distribution: today's #haskell solution shows it's really simple.
- December 8th, 2017: For Friday's #haskell problem we parse NYT article summaries and upload them to a PostgreSQL database. Today's #haskell solution shows that our simple parsing exercise wasn't so simple. Isn't dirty data delightful?
- December 7th, 2017: Throwing the switch with Thursday's #haskell with a hard reset of the database. For today's #haskell solution we do a hard reset: we wipe the recommendation and publish tables and repopulate.
- December 6th, 2017: It's 'kinda' bad to return articles from a search that are already recommended. Wednesday's #haskell problem fixes this. Today's #haskell solution shows what a simple filter notMember can do.
- December 5th, 2017: Tuesday's #haskell problem we narrow our focus and structure our keyword search-space only on keys requested in the NYT archive on PostgreSQL. With a little bit of monadic/applicative magic, we have narrowed keyword searches.
- December 4th, 2017: For Monday's #haskell problem: "But can Haskell do anything useful?" Two words: ... yes.
- December 1st, 2017: For Friday's #haskell problem, what happens when the boss says: "That's good, but ..."? REWORK! THAT's what happens! Today's #haskell solution renders the source article in full and the recommended articles in brief. Got it!

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