The Nineteenth Byte

TuxCopter

11:07 AM

From my understanding it nests the old number in another level of f(x)

Qwerp-Derp

So I want to put in a church numeral, say 1 (which is λf.λx.f x)

Where do I put it in

@TuxCopter Halp if you know the answer?

Laikoni

11:26 AM

@Qwerp-Derp You just apply the successor function to the numeral: (λn.λf.λx.f (n f x)) ( λf.λx.f x) so you "put it in" n: λf.λx.f (( λf.λx.f x) f x) which reduces to λf.λx.f (f x) which is 2.

Qwerp-Derp

Oh cool

Wait where does the beginning λn go

New Sandboxed Posts

0

A: Sandbox for Proposed Challenges

Create an interpolation helper This is similar to this other proposal of mine. I won't delete that one since it has gotten good feedback, and I might come back to it. I think maybe this one is better. If this one is posted then I'll delete the other one (they will almost be duplicates. A polyno...

Qwerp-Derp

Looking at the SO dev survey

Coffeescript is dying, it's slowly getting replaced by ECMAScript6 probably

Zgarb

@Qwerp-Derp I see you got your question answered!

Qwerp-Derp

Kinda, I'm wondering how Laikoni's thing works

Cause I understand you replace n with your Church numeral

But how does the beginning λn get removed

Zgarb

11:40 AM

That's how you apply a lambda term.

Qwerp-Derp

Oh

So is this how it works?

  λnfx.f(nfx)
= λfx.f((λfx.fx)fx)
= λfx.f(fx)

Zgarb

No. Laikoni applied the successor term to 1. Your first line is missing that.

Qwerp-Derp

??

Oh

  (λnfx.f(nfx))(λfx.fx)
= λfx.f((λfx.fx)fx)
= λfx.f(fx)

So like that right?

Ah I understand now, cause the two things in Laikoni's post looked like two separate things and I got confuse

Zgarb

Yeah.

LegionMammal978

You'd have to write it (λnfx.f(nfx))(λfx.fx)

Qwerp-Derp

11:52 AM

Oh so like a function call right

Zgarb

That's true, the scope of a lambda reaches as far right as possible, so you need parens around the successor function.

Qwerp-Derp

  ((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= (λnfx.((λfx.f(fx))f(nfx))(λfx.f(fx))

What's the next stage?

LegionMammal978

@Qwerp-Derp You might need some α-conversion for that

(i.e., change your variable names to avoid conflicts)

Qwerp-Derp

Which variable names do I change

LegionMammal978

The ones in the second function (the number)

Qwerp-Derp

11:57 AM

Oh

LegionMammal978

But yeah, that's why I use de Bruijn indices whenever I lambda calculus :P

Qwerp-Derp

So something like this?

  ((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= (λnfx.((λfx.f(fx))(f(nfx)))(λfx.f(fx))
= (λnfx.((λgy.g(gy))(f(nfx)))(λfx.f(fx))

I changed it to g and y

LegionMammal978

idk, just change all the variable names to something different

Qwerp-Derp

But I want to solve the inner thing first

Do I just sub in g for the f outside it?

LegionMammal978

Lemme figure it out

Zgarb

11:59 AM

Chance all the names right at the start. Makes things easier.

LegionMammal978

^

Laikoni

@Qwerp-Derp The parents around (f(nfx)) are wrong as far as I can tell

Qwerp-Derp

Is this valid alpha-conversion?

  ((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= ((λmnfx.mf(nfx))(λab.a(ab)))(λcd.c(cd))

I think I haven't changed anything vital

@LegionMammal978 De Bruijn indices?

Show me

LegionMammal978

((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= (λλλλ42(321))(λλ1(12))(λλ2(21))
= (λλλ(λλ1(12))2(321))(λλ2(21))
= (λλλ(λ1(13))(321))(λλ2(21))
= (λλλ321(3212))(λλ2(21))
= (λabc.abc(abcb))(λde.d(de))

Pretty much, you replace each variable by its index on the stack

Qwerp-Derp

Ah

So is this not solved yet?

Laikoni

12:03 PM

@Qwerp-Derp seems right to me

LegionMammal978

> = (λabc.abc(abcb))(λde.d(de))

Qwerp-Derp

And then I sub in the final function?

LegionMammal978

yup

> = λfx.f(fx)(f(fx)f)

Qwerp-Derp

@LegionMammal978 I think this is right:

  (λλλ321(3212))(λλ2(21))
= λλ(λλ2(21))21((λλ2(21))212)

Zgarb

@LegionMammal978 Why are the indices of the last two terms on the second line different?

LegionMammal978

12:07 PM

@Zgarb ???

Oh noes, I messed up

Qwerp-Derp

Is this right?

  ((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= (λλλλ42(321))(λλ2(21))(λλ2(21))
= (λλλ(λλ2(21))2(321))(λλ2(21))
= (λλλ2(2(321)))(λλ2(21))

LegionMammal978

@Qwerp-Derp Yes.

Qwerp-Derp

Orrite I think I got it

  ((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= (λλλλ42(321))(λλ2(21))(λλ2(21))
= (λλλ(λλ2(21))2(321))(λλ2(21))
= (λλλ2(2(321)))(λλ2(21))
= (λλ2(2((λλ2(21))21)))
= (λλ2(2(2(21))))

LegionMammal978

  ((λmnfx.mf(nfx))(λfx.f(fx)))(λfx.f(fx))
= (λλλλ42(321))(λλ2(21))(λλ2(21))
= (λλλ(λλ2(21))2(321))(λλ2(21))
= (λλλ(λ3(31))(321))(λλ2(21))
= (λλλ2(2(321)))(λλ2(21))
= λλ2(2((λλ2(21))21))
= λλ2(2((λ3(31))1))
= λλ2(2(2(21)))
= λfx.f(f(f(fx)))

Yup

Qwerp-Derp

gtg

LegionMammal978

12:11 PM

Wait, you have an extra λ at the start

You didn't β-reduce correctly, shame on you

What is this function supposed to do, again?

Oh, it's addition

So λλλλ42(321) is add, and λλλ2(2(321)) is add2?

Ima try and figure out an infinite Church stream of λ1s now

3

Hmm, it comes down to finding a function f that obeys the following:

f(λλ2)      = λλ1
f(λλ1)(λλ2) = λ1
f(λλ1)(λλ1) = f

LegionMammal978

12:40 PM

There, figured it out

f = (λλ1(λλ1)(λ1(λ1)(33)))(λλ1(λλ1)(λ1(λ1)(33)))

Really, you can make an infinite stream of anything by replacing (λ1) with the appropriate value

Martin Ender

Friendly reminder that voting for the Best Of will end in a bit over 11 hours.

aditsu

hmm, I should add Church numerals to my SKI thing

anyway, 0 = KI and increment = S(S(KS)K)

aka successor

mınxomaτ

1:10 PM

@MartinEnder That took me a while to read. My brain ignores every single-line bold message in chat, because they are usually just timestamps.

New Main Posts

1:29 PM

1

Q: Find a Glider Synthesis (Game of Life)

Challenge Summary In summary, the challenge is to provide the glider synthesis for a Game of Life configuration, which is your input. What does this mean? Well, firstly, let me explain a few terms. By Game of Life, I mean Conway's Game of Life. If you don't know what this is, you can read t...

Gabriel Benamy

2:31 PM

alright guys we have 9 hours to upvote my entry to the kansas city shuffle another 12 times

Gabriel Benamy

2:47 PM

codegolf.stackexchange.com/a/4491/60884 As someone who doesn't do C, would main(){puts("2012"=="2012"?"2012":"2012");} also be valid?

New Sandboxed Posts

0

A: Sandbox for Proposed Challenges

Avoiding Averages Given a non-empty list of positive integers, reorder the list such that for every pair of indices, the average of the values at those indices is not contained in any index between them. Rules This is code-golf so the shortest code wins.

Business Cat

Couldn't you change that to main(){puts("2012"=="2012"?"20512":"2012");}and have it print 20512?

Gabriel Benamy

oh right

I feel dumb now

Anonymous

Did the MathJax bug with code blocks and search results ever get fixed?

Downgoat

3:04 PM

@Mego i bellieve so

Can't find link however

Aha:

@200_success Delimiters changed. Enjoy! — Pops ♦ Apr 7 '14 at 19:47

orlp

3:27 PM

I think it's pretty funny that my RSA cop posts were super controversial, but people liked the robber's posts @Sp3000

@GabrielBenamy you can't compare strings with ==

Nathan Merrill

I'm pretty sure liking is equivalent to starring things here.

orlp

that is, not generally

it compares the address of the string

but nothing prevents the compiler from putting one string in a different location than the other

mınxomaτ

3:39 PM

I wondered why my browser ran out of memory when I tried to change my twitter avatar, until I noticed that I rendered my avatar as a 15,000 px² image.

orlp

3:59 PM

@mınxomaτ even then that's still only ~650 mb uncompressed, assuming 24bpp

mınxomaτ

My laptop has 2GB of RAM.

Matthew Roh

4:20 PM

Damn

Does it work properly

wat

@mınxomaτ My sister's laptop is ALMOST the same as mine

except it has 2gb RAM instead of 4GB

and a slightly slower CPU

quartata

@NewMainPosts are we for real right now

Matthew Roh

Should I make a question about twitter snowflakes

Anonymous

@quartata I know that's a dupe of something

quartata

Yeah, it's called "Hello, World!".

Anonymous

4:31 PM

I don't know if I'd close it as a dupe of HW

Anonymous

A challenge that was also "print this thing N times" would be better

wat

WHy do things get closed as duplicates of:

a. Hello world

b. Never gonna give you up

quartata

Because they were the first constant output challenges

wat

Even though some of the outputs are completely different and can be optimized in different ways...

Anonymous

I can't find a "repeat this N times separated by newlines" challenge to use as a dupe target, though I'm sure we've had one

quartata

4:42 PM

@wat There's no real structure to this one that can be exploited

mınxomaτ

Huh, the TDM-GCC branch of DevCpp surpassed 10 million (took them 6 years) downloads this year.

quartata

aside from regular deflate compression

and having a goat printing built-in for some inane reason

wat

@quartata That's true I guess

Anonymous

Because goats are funny!!!!11!1

Anonymous

Seriously, the people who run jokes into the ground ruin things for everyone. It really needs to stop. The goat stuff was funny at one point, but it's not even beating a dead horse anymore - they're punching a bottle of glue.

Gabriel Benamy

4:45 PM

you could say they're

beating a dead [gets punched in the face before he can finish his sentence]

2

TIL macs do not have hard drives

DJMcMayhem

That's not even close to true

wat

...

the challenge text is more correct than the comment

TuxCopter

@wat codegolf.stackexchange.com/revisions/107721/8 Why did you add ## after each title? It's useless

wat

Looks better in the source

also I fixed a few formatting at the same time

DJMcMayhem

5:33 PM

Am I the only one who thinks this conversation doesn't make any sense?

Anonymous

@DJMcMayhem Most conversations with that user don't make sense.

wat

@DJMcMayhem makes a lot of sense to me

Kritixi Lithos

If there are only 4 candidates, does that mean all of them are going to be ROs?

mınxomaτ

@noɥʇʎԀʎzɐɹƆ The mods will be taking care of the actual election phase, so you should direct any questions regarding it towards them. — Mego yesterday

Gabriel Benamy

I wish there were a place where people could post their golfing process. When I answer questions in Perl, I usually have a text document open with the history of all of my golf attempts as they got shorter and shorter. I think it would be interesting for people to post things like that so other golfers can get a better idea of what tricks they can use.

And I don't mean like, in the edit history; I usually try things out for about half an hour after I get a working solution to see if I can get it shorter.

While PPCG is quite clearly a competition of sorts, especially between users of the same language, I also like to think that it's a learning experience for everyone involved. Just seeing the end product doesn't necessarily give us usable insights of our own.

Anonymous

5:52 PM

@GabrielBenamy Include it in the answer body. Lots of people (myself included) are interested in reading others' processes for golfing.

Mistah Figgins

I have large graph paper for 2d languages

And I got hexagonal paper recently for hexagony :)

Gabriel Benamy

@MistahFiggins One day I'm gonna learn to use HBCIHT

Mistah Figgins

What's that?

Gabriel Benamy

Are there any TC languages in which quines are not possible?

esolangs.org/wiki/Half-Broken_Car_in_Heavy_Traffic

Mistah Figgins

impossible is not the same as completely improbable

@GabrielBenamy What's HBCIHT? Acronym, i assume

Gabriel Benamy

5:58 PM

the link I posted

TuxCopter

Half-Broken Car In Heavy Traffic

Anonymous

@GabrielBenamy I'm fairly sure the answer is no. A TC language can do anything a TM can by definition, and since a TM can do a quine, any TC language can also do a quine. It's considerably harder in some languages (especially the ones that fight you), but it should still be theoretically possible.

Mistah Figgins

Ah, got it, thanks

@Mego HBCIHT doesn't fight you so much as throw you into a fiery hellscape

Gabriel Benamy

@Mego But "print a quine" doesn't fundamentally do the same thing in every language. If I wrote a language that can only output numbers and has no concept of letters / non-numerics, would that language be considered TC? Would a quine in that language be possible if its instructions were all non-numeric?

Anonymous

It would be complicated.

Anonymous

6:02 PM

I don't really have the time or inclination to ponder such puzzles right now.

Business Cat

I imagine in that case it would print the byte values for the source code, rather than print the characters directly

Or something like that

TrojanByAccident

Can someone explain to me HBCIHT? Where does the pointer start? Which direction does it go in?

Business Cat

o is the car's (the pointer's) initial position. It starts moving in a random direction (up, down, left, or right)

DJMcMayhem

@Mego the original version of brain flak could only output numbers, so a quine was definitely not possible, even though it was TC

Of course, you could output the quine in ASCII values, but I don't know if that counts

Gabriel Benamy

Should we get a Meta ruling?

Mistah Figgins

6:07 PM

What's the consensus on editing others' answers to shave a byte off?

Anonymous

Encoding shenanigans are a possibility with quines

Business Cat

I'd be surprised if hasn't been asked already, let me search

Anonymous

@MistahFiggins Don't

Mistah Figgins

B/c there's an edit waiting to be reviewed that does exactly that

TrojanByAccident

@BusinessCat Then how can you code like that?

Anonymous

6:09 PM

Reject as conflicting with author's intent

TuxCopter

@TrojanByAccident You don't.

Gabriel Benamy

@TrojanByAccident with great difficulty

TrojanByAccident

@MistahFiggins Yeah, don't. Suggest it to them in a comment

Mistah Figgins

@TrojanByAccident Done

TrojanByAccident

@TuxCopter Helpfulness of the year 10/10

Anonymous

6:11 PM

@TrojanByAccident You have to prepare for each possibility

Mistah Figgins

@Mego Like I said, fiery hellscape

TrojanByAccident

I'm officially going to learn no comment

New Main Posts

2

Q: The Tax Historian

Introduction There is a tax collector that has some trouble managing the taxes of his kingdom: the historical records have burnt down in a great fire. He wants to find out how many possible pasts there could be in terms of where the current money was inherited from. Luckily, his kingdom is very...

fastest-code cellular-automata

Poke

@MistahFiggins speaking of fiery hellscape

we won that game

Kritixi Lithos

6:40 PM

@Poke Woah, there are elephants in AOE2

Poke

yeah man. aoe2 is still getting updates

a+ game

Kritixi Lithos

There's an online edition?

Poke

@KritixiLithos store.steampowered.com/app/221380

Kritixi Lithos

Is there an aoe3? (that's the only game in the aoe series I've played)

Poke

yeah there is

wizzwizz4

6:48 PM

What characters are allowed in a domain?

Is it printable ASCII sans ., /, ?, % and ``?

TrojanByAccident

@wizzwizz4 I think it's only alpha-numerics and -

wizzwizz4

@TrojanByAccident Ok. Thanks.

Do you know of a random string generator that only contains alpha-numerics and -?

TrojanByAccident

@wizzwizz4 I shall provide, give me a minute

wizzwizz4

@TrojanByAccident Never mind; I've found random.org.

Gabriel Benamy

@wizzwizz4 @TrojanByAccident it also can't start or end with a hyphen

TrojanByAccident

6:52 PM

@wizzwizz4 Alright

@wizzwizz4 I don't see an option on there?

wizzwizz4

@TrojanByAccident It doesn't have hyphens, but it's close enough.

TrojanByAccident

I guess

wizzwizz4

You could write a JavaScript site if you like; linking here might boost your SEO (especially with lots of users who might link further).

I would, but I'm too busy even to golf right now! :-/

TrojanByAccident

lol

I might add a page to my github

not right now though

I'll write up a generator though, just 'cuz

Poke

7:08 PM

[RFC 1738](https://www.ietf.org/rfc/rfc1738.txt)
The fully qualified domain name of a network host, or its IP
address as a set of four decimal digit groups separated by
".". Fully qualified domain names take the form as described
in Section 3.5 of RFC 1034 [13] and Section 2.1 of RFC 1123
[5]: a sequence of domain labels separated by ".", each domain
label starting and ending with an alphanumerical character and
possibly also containing "-" characters. The rightmost domain
label will never start with a digit, though, which

New Main Posts

0

Q: Total Derangement

The problem: Write a function which, given a cycle length n and a number of cycles m, where 'm' is between 1 and n-1, generate m random cycles, each of length n, and all of which are derangements of each other. What is a cycle? Imagine you're hopping around a list. Each element in the list is a...

combinatorics permutations fastest-algorithm

Poke

i did the hyperlink thing correctly... why is it weird

wizzwizz4

@Poke So, if SE create the subdomain 123.stackexchange.com, they'll only be able to have a meta site?

TrojanByAccident

@Poke markdown breaks when you make it multi-line

mbomb007

I just found out that I'm the top reviewer of all time for the meta site.

fist pump

wizzwizz4

7:12 PM

@mbomb007 I just found out that I'm not the top reviewer of all time for Retrocomputing.

antifist pump

TrojanByAccident

@wizzwizz4 it should be fine, 123.com

Poke

@wizzwizz4 The rightmost domain label can't start with a digit so I think that would still be ok because "com" is the rightmost label

wizzwizz4

@Poke ... Rightmost... :-/

Poke

@TrojanByAccident til, thanks

wizzwizz4

I was just testing.

TrojanByAccident

7:13 PM

@Poke np

mbomb007

@wizzwizz4 I did > 10% of all reviews on the meta site. :O

I'm surprised. I guess other people don't check that queue as often.

wizzwizz4

@mbomb007 Oh. Now I feel better about the quantity that I've done.

@mbomb007 For some reason people don't check Meta.

I don't know why.

I also don't check Meta though... :-/

Business Cat

Because I hardly even see things on the main site's review queue.

mbomb007

@BusinessCat More review queues are made available at 2000 rep (though you can possibly still see them?)

But yeah, people handle them much faster

Business Cat

I can't see them, just the basic 6

wizzwizz4

7:20 PM

@BusinessCat I think those are the only ones.

Apart from the mod queue, which isn't technically a review queue at all and (iirc) is only shown to ♦s.

Business Cat

Well, I have access to the 6 that I can see

Kritixi Lithos

I also have access to 6

wizzwizz4

I have access to 6, plus the Meta Reviews button, plus the mod queue.

So, six.

mbomb007

Ah, I misread the permissions descriptions. All queues are available at 1K rep on PPCG.

126

A: What are the review queues, and how do they work?

What is a "review queue"? Review queues (also known as review tasks) contain posts that possibly need community attention, as determined by the system or other community users. You are shown these posts, one at a time, and you "review" them. Like flagging, there are badges for this. So, what co...

Riker

@wizzwizz4 SO also has like 4 more of its own

no other sites have them

wizzwizz4

7:29 PM

@Riker That's how I knew that any review queues would be the same on Programming Puzzles & Code Golf as on Retrocomputing.

Riker

ah yeah I thought you were just talking about them in general

not just PPCG/RC

wizzwizz4

@Riker We were actually just talking about PPCG, but I checked RC to make sure there weren't any hidden ones.

Riker

ah okay

wizzwizz4

Though, you never know...

Dennis is mysterious.

New Sandboxed Posts

0

A: Sandbox for Proposed Challenges

Guide the Alphabet Given an array of directions, where the directions are defined as follows: NW N NE W . E SW S SE As indexes (you may use these indices for directions instead of the strings above): 0 1 2 3 . 4 5 6 7 Generate the corresponding alphabet String that represents the d...

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