explain xkcd - User contributions [en]

2453: Excel Lambda

2022-02-02T20:11:51Z

108.162.219.169: replaced an "he" with a "they" and a "his" with a "their"

{{comic
| number = 2453
| date = April 21, 2021
| title = Excel Lambda
| image = excel_lambda_new.png
| titletext = Extremely rude how Turing's later formulations of the halting problem called me out by name specifically.
}}

==Explanation==
[[Cueball]] is computing and [[Ponytail]] criticizes him in a way that is reminiscent of the [[:Category:Code Quality|Code Quality series]], although not as harsh. Cueball has lots of strange [[:Category:Cueball Computer Problems|computer problems]], and this will most likely result in another one.

The comic begins with Ponytail finding out that {{w|Microsoft Excel}} is adding a {{w|Anonymous_function|lambda function}} to their function library. This was [https://techcommunity.microsoft.com/t5/excel-blog/announcing-lambda-turn-excel-formulas-into-custom-functions/ba-p/1925546 announced by Microsoft] for Beta users in December of 2020, but perhaps Ponytail has only discovered this recently. A lambda function is a fundamental mathematical structure that can (alternatively) be used to completely define all possible computations from the ground up, in what is known as {{w|lambda calculus}}, other than using for-loops, pointers and effect-ful functions that bear little resemblance to mathematical functions. They are commonly found in programming languages such as {{w|Lisp}}, {{w|Python}}, and many others. A lambda function is also called an {{w|anonymous function}} because in most languages it can be passed to other functions (including another lambda function) without needing to be given any formal name during coding, or given {{w|Closure_(computer_programming)|'closure'}} under whatever name(s) its calling procedures desire.

Finding that Excel is adding a lambda function pleases Ponytail. Cueball claims that the lambda function is unnecessary, as when he needs arbitrary computation he just adds a block of columns to the side of his sheet and has a {{w|Turing machine}} process it. This would technically work as lambda calculus is formally equivalent to Turing machines. People have created [https://www.felienne.com/archives/2974 Turing machines in Excel], although not for practical purposes.

Ponytail finds his solution absurd and is convinced Cueball is "doing computing wrong". But he claims that all computing is equally wrong, citing the {{w|Church-Turing thesis}}, a hypothesis which says that a function can be computed by executing a series of instructions if and only if that function is computable by a Turing machine. A classical Turing machine uses an infinitely long strip of tape as its memory; for Cueball, the large Excel column acts as the "tape". All ways of computing are "equally wrong" since, according to this thesis, they can all be translated to or from a Turing machine.

Ponytail and Cueball appear to have different ideas of 'computing'. Ponytail, like most programmers, probably includes efficiency and readability as important characteristics of 'doing computing right'. Cueball appears interested only in {{w|computability}}, a more theoretical point of view than Ponytail's.

Ponytail then says that Turing would change his mind if he saw Cueball's spreadsheet, presumably because of the extreme complexity of Cueball's code in the spreadsheet. Cueball's final statement is that Turing could ask him to stop, but would not be able to prove if he actually will stop.

Cueball's final statement is a reference to the {{w|halting problem}} mentioned in the title text. It is the problem of determining whether a given Turing machine will halt. The problem has been shown to be undecidable, i.e., it is impossible to build an algorithm that computes whether any arbitrary Turing machine will halt or not. Because of the way Cueball has behaved, he has been specifically mentioned in Turing's later formulations of the halting problem. Cueball finds this very rude. This is of course a joke, since Turing has been dead since 1954,{{citation needed}} presumably long before Cueball was born. But it would be crazy indeed if a scientist became so mad at a person that they would mention this person by name in their formulation of a serious problem.

Over-complicated spreadsheets were also mentioned in [[2180: Spreadsheets]].

While conditional loops with the ability to interact with the loop variable, and functions reading and altering parameters ''not'' passed to it, can be (ab)used creatively to great effect, the fact a same structure may have been vastly different control schemes puts burden on anyone reading preexisting code. Functional programming abstracts computation differently, and uses distinct constructs for plain iterating over a list ('''map''' and co., the inner function is forbidden to interact with the accumulator by semantics) and recursion and iteration with side-effects or implicit input (modeled as various flavors of monads). Constructs like '''map''' take functions as parameter, but giving every tidbit of code a name and hiding it 100+ lines away nullifies the readability. Lambda function is thus a much needed piece for a functional style of expression.

In the Excel example though, the point is you can finally create custom functions in the original '''formula''' language, not some too-powerful-not-to-be-abused-by-hackers macro language that any security-aware person would strip out before opening an Excel spreadsheet. Excel formulas take only explicit input (cells) and have explicit and controlled output (cells or function return value), fitting the Lambda notion nicely. Combine this with proper recursion support and you have a language that becomes Turing-complete without relying on evaluator abuse ([https://chandoo.org/wp/timestamps-excel-formula-help/ circular reference and F7 for next iteration]) or a [https://www.felienne.com/archives/2974 ''wall'' of Turing machine states]. Now one can '''express''' (pseudo-code follows) CellValue=iterate(recursive-function, num-of-steps) properly, with num-of-steps as an input not *number of F7 presses* or *starting value of a cell which get decremented to zero as recursion proceeds* or *row number from wall of states*. Excel probably still tracks the iteration with a variable in calculating the final value, but that implementation detail is decoupled from the language itself.

An example of a lambda function in Python that takes a parameter named '''a''' and computes the value '''a'''-squared minus 1:

lambda a: (a ** 2) - 1

Lambda values are often used as parameters to other functions, such as '''map''' which applies a function to each item of an "iterable" such as this list of the numbers 1, 2, and 3:

map(lambda a: (a ** 2) - 1, [1, 2, 3]) ''# will generate the values 0, 3, and 8''
You can copy/paste this statement into a Python interpreter (such as [https://www.tutorialspoint.com/execute_python_online.php TutorialsPoint]) to see it work (do not copy the leading spaces; that's a wiki thing):
print(list(map(lambda a: (a ** 2) - 1, [1, 2, 3])))

In the above example, '''map''' takes each element of the list containing the values 1, 2, and 3 in turn, sending each value to the lambda function (as the parameter "a") and so generating the sequence of values: 0, 3, and 8. These are then reconstructed into a '''list''' to '''print''' the complete result: '''[0, 3, 8]'''.

A recursive lambda might be:

def pointless_recursion(v):
# If current value (x) is evenly divisible by 4, return the source (v) * current (x)
# Otherwise, print current, and then try the process again with the current value of x + 3
r = lambda x: x * v if x % 4 == 0 else print(x) or r(x + 3)
return r(v)

pointless_recursion(12) # returns 144 (i.e., 12*12)
pointless_recursion(11) # prints 11, 14, 17 then returns 220 (i.e., 20*11)

In this instance, the function is given the name 'r', and features a (conditional) call back to this self-same 'r' within it. The 'x' is whatever value is the latest passed to 'r', while 'v' is that which was first passed to the container function.

Ideally, such techniques should be used to ''reduce'' {{w|Spaghetti code}}, not increase it. But this isn't a foregone conclusion, especially in Cueball's hands.

==Transcript==
:[In a narrow panel, Ponytail is walking in from the left, looking down at her phone]
:Ponytail: Oh cool, Excel is adding a lambda function, so you can recursively define functions.

:[Ponytail, holding her phone to her side stands behind Cueball, who is sitting in an office chair with a hand on a laptop standing on his desk. He has turned around to face her, leaning with the other arm on the back of the chair.]
:Cueball: Seems unnecessary.
:Cueball: When I need to do arbitrary computation, I just add a giant block of columns to the side of my sheet and have a Turing machine traverse down it.

:[In a frame-less panel Ponytail is standing in he same position behind Cueball, who has resumed working on his laptop with both hands on the keyboard.]
:Ponytail: I think you're doing computing wrong.
:Cueball: The Church-Turing thesis says that all ways of computing are '''''equally''''' wrong.

:[Ponytail is still behind Cueball, who has a finger raised in the air, and the other hand is on the desk. Cueball's head has a visible sketch layer which has not been erased.]
:Ponytail: I think if Turing saw '''''your''''' spreadsheets, he'd change his mind.
:Cueball: He can ask me to stop making them, but not prove whether I will!

==Trivia==
*In the [https://www.explainxkcd.com/wiki/images/3/3b/excel_lambda.png original version] of the comic, in the final panel, there was a gray pencil outline, slightly different to Cueball's head that had not been removed.
**This was later fixed in a re-upload.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring real people]]
[[Category:Computers]]
[[Category:Spreadsheets]]
[[Category:Programming]]

1578: Squirrelphone

2015-09-16T16:08:33Z

108.162.219.169: Not a portmanteau: portmanteaux share letters.

{{comic
| number = 1578
| date = September 16, 2015
| title = Squirrelphone
| image = squirrelphone.png
| titletext = After a while, the squirrel starts making that beeping noise and doesn't stop until it hops back up onto the stump.
}}

==Explanation==
A "squirrelphone" is a compound word combining "{{w|squirrel}}" and "{{w|phone}}".

In this comic, we see a squirrel pretend to be a telephone, only to bite [[Cueball]] who tries to pick it up and use it as one. This is humorous because a living squirrel is not an appropriate creature to maintain a phone call{{Citation needed}}. This could be seen as an example of mimicry in Nature, or parasitism where one creature gains a benefit from another.

It is an allusion to the vampire squirrel documented over the weekend that allegedly 'attacked and killed' a deer. The comic follows the absurd conclusion that the squirrel uses mimicry to 'attack and kill' humans. [[Cueball]] is lucky to still be alive{{Citation needed}}.

The sounds the squirrel makes correspond to the tones that the terminals made when you used the POTS (Plain Old Telephone Service) in the US:
* When someone else called you and the receiver of your phone was on the hook, the phone made loud and long "riiing riiiing" tones. --- This is the case in the first frame of the comic.
* When you picked the receiver up, the phone call was established and no extra noises were made.
* When no phone call was established and you picked up, a continuous humming tone was heard, meaning the service was up and you could dial someone else's number. (A {{w|dial tone}})
* When no phone call was established but dialling was not possible, short "bip bip bip bip" tones (known as "fast busy") were heard. This happened either when an existing call ended or was interrupted or you had had the receiver off hook for too long (about half a minute) without dialing --- This is the case in the title text of the comic ---. In this case, you should hang up so that you can receive calls or pick the receiver up again and dial.

==Transcript==
:[Cueball is approaching a stump with a squirrel perched on it. A ringing noise is coming from the squirrel's back.]
:Squirrel: Riiiiing
:Squirrel: Riiiiiing

:[Cueball has picked up the squirrel and is holding it to his left ear]
:Cueball: Hello?

:[The squirrel bites Cueball's head]
:Squirrel: Chomp!
:Cueball: Ow!

:[Cueball holds his hand to his cheek while the squirrel leaps away, fleeing]
:Cueball: ???

{{comic discussion}}

[[Category:Squirrels]]
[[Category:Comics featuring Cueball]]
[[Category:Portmanteau]]

654: Nachos

2014-11-24T02:22:38Z

108.162.219.169: /* Explanation */

{{comic
| number = 654
| date = October 26, 2009
| title = Nachos
| image = nachos.png
| titletext = Hey, gaming on wifi? You have only yourself to blame.
}}

==Explanation==
{{incomplete|Maybe mention that the whole microwave-wifi interference thing is a myth?}}
[[Megan]] and [[Ponytail]] are playing an online shooter game. Ponytail calls [[Cueball]], who is living with Megan, and "subtly" persuades him to make {{w|nachos}}. {{w|Wi-Fi}} and {{w|microwave oven}}s both use {{w|ISM band|radio frequencies around 2.4 GHz}}, so Cueball's cooking disrupts her connection and allows Ponytail to kill Megan's online character.

The title text points out that Megan has only herself to blame, as gaming on wifi is more susceptible to such issues than gaming with a wired connection (e.g. {{w|Ethernet}}).

==Transcript==
:[Cueball is on the phone with Ponytail, who's on her computer in the other half of a split panel.]
:Cueball: Hello? ... Oh, hey. Looking for Megan? She's gaming.
:Ponytail: I know. You know what's delicious? Nachos.

:[Ponytail clicks on her computer while talking.]
:Ponytail: When you layer the cheese so it gets on every chip... then smother them in sour cream and salsa...

:Cueball: Mm, that IS delicious. And I've got the ingredients, too!
:Ponytail, on phone: You should make some!
:Cueball: I will!
:Ponytail, on phone: Hurry.

:[Cueball is making nachos in the microwave.]
:Microwave: ''beep beep whirrrr''

:Megan, at her computer: My wifi signal!

:[Ponytail who called is at her computer.]
:Computer: Boom! Headshot.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]

Talk:1438: Houston

2014-10-24T17:22:32Z

108.162.219.169: throwing in an alternative interpretation: cueball as a basement dweller script kiddie

A commentary on the nature of outsourced helpdesks, perhaps? Although, IME, the problems are more due to 'sticking to a script' (which would have given an entirely different exchange) rather than an unknowledgable and casually uninterested 'service'-person. [[Special:Contributions/141.101.98.247|141.101.98.247]] 05:15, 24 October 2014 (UTC)
:I think this is the idea behind the comic too. Kind of like a "What if it had happened today?" It sure sounds like the kind of hotline support we get today. [[User:Deantwo|Deantwo]] ([[User talk:Deantwo|talk]]) 10:29, 24 October 2014 (UTC)

::I agree. This is definitely comparison between the original mission control center and current outsourced helpdesk centers. Although it would be interesting to know what specific incident caused Randal to comment on it. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 12:28, 24 October 2014 (UTC)

What is going on is this strip? Usually it's a reference to something or a commentary, but I don't get it at all. [[User:Cheeselover724|Cheeselover724]] ([[User talk:Cheeselover724|talk]]) 05:32, 24 October 2014 (UTC)

I think I figured out enough of it to remove the "incomplete" tag. This is definitely one of the weird ones. [[User:Shachar|Shachar]] ([[User talk:Shachar|talk]]) 06:02, 24 October 2014 (UTC)

Reference to Continuum? (Canadian sci-fi show)
[[Special:Contributions/199.27.133.106|199.27.133.106]] 06:41, 24 October 2014 (UTC)

Ebola? Really? Where is that..what? [[Special:Contributions/173.245.49.79|173.245.49.79]] 09:34, 24 October 2014 (UTC)

I agree, there is no evidence to back up the ebola reference. [[User:Djbrasier|Djbrasier]] ([[User talk:Djbrasier|talk]]) 09:36, 24 October 2014 (UTC)

Also, I took it to refer to people being distracted on the phone in general (hence the title text) or generally not taking their jobs serious. Maybe the idea that for NASA, space travel has become so routine that mission control is no longer as engaged in the missions. [[User:Djbrasier|Djbrasier]] ([[User talk:Djbrasier|talk]]) 09:38, 24 October 2014 (UTC)

Perhaps the guy answering the phone is called "Houston"? A misplaced Skype call from a rather shell shocked astronaut? {{unsigned ip|141.101.99.111}}
:But then it wouldn't make sense, that he says he's at work.--[[Special:Contributions/173.245.49.29|173.245.49.29]] 13:36, 24 October 2014 (UTC)

There are a LOT of anachronisms, or things that don't match the way things were back in the 1960's, not just the flat screens. (And I do still remember the sixties, despite "if you can remember the sixties, you wern't really there" - a reference to the drug scene.) We didn't say "cool" or "you suck at doing that" back then, and it's very unlikely that communications with the mission and a simple telephone call would be selectable from the same headset, and the michrophones on headsets were larger and probably had dangling wires back then. --[[User:RenniePet|RenniePet]] ([[User talk:RenniePet|talk]]) 13:22, 24 October 2014 (UTC)

It could be a commentary on privatizing space travel by NASA (among others to Boeing). Would explain, why Cueball knows it's a "airplane or whatever".--[[Special:Contributions/173.245.49.29|173.245.49.29]] 13:36, 24 October 2014 (UTC)

I understand it's a reference, but is this supposed to actually be the Apollo 13? I understood it was just another mission happening today. I find the anachronism explanation nonsensical. [[Special:Contributions/108.162.212.211|108.162.212.211]] 13:57, 24 October 2014 (UTC)

"At first glance, this comic appears to be an "alternate reality" view at what could happen today, given that most people in the XXI century seem to suffer ADD." I don't think that we can assume this at all. Also, that's not what ADD is. [[User:Lomky|Lomky]] ([[User talk:Lomky|talk]]) 14:16, 24 October 2014 (UTC)
:Yeah. I think it's far more clear that Randall's commenting on unhelpful tech support than anyon'es short attention span. I've edited the explanation above. [[Special:Contributions/199.27.128.146|199.27.128.146]] 15:34, 24 October 2014 (UTC)

Did Randall have a bad experience with a call center operator? [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]]) 14:38, 24 October 2014 (UTC)

Can someone explain why this is supposed to be funny? The explanation page doesn't quite get there.

Am i the only one interpreting Cueball as a script kiddie with too much spare time who somehow managed to hijack the communication line between Apollo 13 and Houston? The alt text is consistent with the basement dweller stereotype. Wouldn't explain the other call though.[[Special:Contributions/108.162.219.169|108.162.219.169]] 17:22, 24 October 2014 (UTC)