explain xkcd - User contributions [en]

Talk:1312: Haskell

2014-01-03T17:03:30Z

108.162.231.13: reorder comments by timestamp, reply

"Thus, it is possible to have a variable representing the entire infinite list of Fibonacci numbers."
Except that Haskell has no variables- nothing is mutable, as they say. You could certainly write a function that generates an infinite list of Fibonacci numbers when called (and lazily evaluated later), but it won't be bound to a variable. If it was, then the list would take up an infinite amount of memory, and lazy evaluation would be pointless.

I will, however, leave the above word "variable" in the explanation, because I can't come up with a concise way of explaining the above.
--[[User:Someone Else 37|Someone Else 37]] ([[User talk:Someone Else 37|talk]]) 09:07, 3 January 2014 (UTC)

:"Expression?" I don't know Haskel, but that's what I would call it in another functional language. --[[User:Rael|Rael]] ([[User talk:Rael|talk]]) 16:31, 3 January 2014 (UTC)
::That's a little imprecise, as it doesn't capture the idea of binding a value to a single symbol. [[Special:Contributions/108.162.231.13|108.162.231.13]] 17:03, 3 January 2014 (UTC)

:The sentence you quote is entirely correct... but might itself require further explanation!
:*Haskell variables aren't mutable, but they are nonetheless referred to as "variables". It's an appeal to the (earlier, after all) use of the word in maths, rather than in imperative programming languages. (No shortage of variables in algebra, geometry, calculus, topology... And no mutation involved.) One might equally say "symbol", "constant", or indeed "symbolic constant".
:*One can bind the fibonaccis to a variable (... constant, 0-place definition, etc) quite happily. In fact, that's the idiomatic way to do it, as it avoids the degenerate complexity of a naive recursive function. It's still evaluated lazily, all the same. (Meaning that it will take an infinite amount of memory... if you run it for an infinite amount of time, and never "consume" the result in any way.)
:*Equally, one can regard such top-level symbol definitions as functions with no arguments, if that's more helpful. [[Special:Contributions/108.162.231.13|108.162.231.13]] 16:42, 3 January 2014 (UTC)

Does anyone have a clue what the Incomplete flag refers to? This seems like a pretty good explanation to me. --[[User:Mynotoar|Mynotoar]] ([[User talk:Mynotoar|talk]]) 11:22, 3 January 2014 (UTC)

Example programs written in Haskell are: pandoc, universal markup converter; git-annex, tool to manage large files in git DVCS. --[[User:JakubNarebski|JakubNarebski]] ([[User talk:JakubNarebski|talk]]) 11:37, 3 January 2014 (UTC)

Talk:1312: Haskell

2014-01-03T16:42:06Z

108.162.231.13:

"Thus, it is possible to have a variable representing the entire infinite list of Fibonacci numbers."
Except that Haskell has no variables- nothing is mutable, as they say. You could certainly write a function that generates an infinite list of Fibonacci numbers when called (and lazily evaluated later), but it won't be bound to a variable. If it was, then the list would take up an infinite amount of memory, and lazy evaluation would be pointless.

I will, however, leave the above word "variable" in the explanation, because I can't come up with a concise way of explaining the above.
--[[User:Someone Else 37|Someone Else 37]] ([[User talk:Someone Else 37|talk]]) 09:07, 3 January 2014 (UTC)
:The sentence you quote is entirely correct... but might itself require further explanation!
:*Haskell variables aren't mutable, but they are nonetheless referred to as "variables". It's an appeal to the (earlier, after all) use of the word in maths, rather than in imperative programming languages. (No shortage of variables in algebra, geometry, calculus, topology... And no mutation involved.) One might equally say "symbol", "constant", or indeed "symbolic constant".
:*One can bind the fibonaccis to a variable (... constant, 0-place definition, etc) quite happily. In fact, that's the idiomatic way to do it, as it avoids the degenerate complexity of a naive recursive function. It's still evaluated lazily, all the same. (Meaning that it will take an infinite amount of memory... if you run it for an infinite amount of time, and never "consume" the result in any way.)
:*Equally, one can regard such top-level symbol definitions as functions with no arguments, if that's more helpful. [[Special:Contributions/108.162.231.13|108.162.231.13]] 16:42, 3 January 2014 (UTC)

:"Expression?" I don't know Haskel, but that's what I would call it in another functional language. --[[User:Rael|Rael]] ([[User talk:Rael|talk]]) 16:31, 3 January 2014 (UTC)

Does anyone have a clue what the Incomplete flag refers to? This seems like a pretty good explanation to me. --[[User:Mynotoar|Mynotoar]] ([[User talk:Mynotoar|talk]]) 11:22, 3 January 2014 (UTC)

Example programs written in Haskell are: pandoc, universal markup converter; git-annex, tool to manage large files in git DVCS. --[[User:JakubNarebski|JakubNarebski]] ([[User talk:JakubNarebski|talk]]) 11:37, 3 January 2014 (UTC)

1308: Christmas Lights

2013-12-25T11:38:13Z

108.162.231.13: Removed some errors and changed the bit about the star in the tree because it's not a global tradition to put a star on top

{{comic
| number = 1308
| date = December 25, 2013
| title = Christmas Lights
| image = christmas_lights.png
| titletext = Merry Christmas from xkcd!
}}

==Explanation==
{{incomplete|Check grammar and add details about the star spectrum}}
Understanding this comic requires knowing about electromagnetic spectra.
In a nutshell, an electromagnetic spectrum is the scientific way of representing the amounts and type of radiation than a specific source emits. In this comic appears a subtype of these, a light spectrum, that shows the visible radiation, some infrared and some ultraviolet. More detailed info on wikipedia({{w|Electromagnetic spectrum}}).

There are 4 graphs in this comic:

In the center of the image, between the couple Cueball and Megan and Beret Guy appears a light spectrum of a fire, notably because it emits a lot of energy in the infrared band (The left zone of the spectrum), and in the red and orange zone (typical colors of a fire)

In the right of the comic appear some spectra shaped in the form of a Christmas tree. There are 3 different spectra in this "Christmas tree":

In the top appears a complex spectrum, probably that of a white LED (see [http://led-brdf.wikispaces.com/Introduction+to+LEDs here]), representing the tradition in some countries of putting a star in the top of the Christmas tree, which represents the star that guided the Three Wise Men in Christianity.

In the branches there are two simpler spectra, one with a peak in the green zone, representing a green LED, and other with a peak in the red zone, representing a red LED.

==Transcript==
{{incomplete transcript}}

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Beret Guy]]
[[Category:Comics with color]]