Hacker News Reader

fexlon There's something off about LED bulbs

I've noticed that LED bulb packages say they'll last several years, but so many of them die after just a year or so. I should start tracking this precisely, but I've just gotten the sense that they often die prematurely.

fexlon A man who invented lithium-ion battery at 57 has an idea for a new one at 92 (2015)

I got that impression too, but it does say "But the path he has chosen involves one of the toughest problems in battery science, which is how to make an anode out of pure lithium or sodium metal."

I suppose that implies he's trying to make an anode out of pure lithium or sodium, but you never know with science journalism.

fexlon A man who invented lithium-ion battery at 57 has an idea for a new one at 92 (2015)

"When the battery is discharging ... positively charged ions shuttle from the anode to the cathode"

I thought that electrons shuttle from the anode to the cathode.

fexlon A Victoria man has gone two decades without money

I never understood the animus against saving. Saving just means you have produced more than you consumed, and I admire that.

fexlon What's Really Warming the World?

I opened the "Summary for Policymakers" listed right on their home page, and it popped up a PDF titled "AR5_SYR_FINAL_SPM-1.pdf". That's where I searched on the word "vapor" and found only one occurrence -- inside the word "evaporation".

I guess the "for the Physical Science Basis" report is something different that I haven't found yet.

fexlon What's Really Warming the World?

Yes I understand that effect, and it makes sense that higher temperatures might cause more CO2 to come out of solution, as in a bottle of soda going flat more quickly at room temperature than in the refrigerator.

That said, I am not certain that the recent dramatic spike to 400 ppm of CO2 (from what I've read) could be entirely caused by the fairly moderate temperature rises measured in recent years.

fexlon What's Really Warming the World?

I searched on the words "vapor" and "vapour" and found nothing. I also search on the word "water" and found nothing relevant to my question.

fexlon What's Really Warming the World?

Sorry, I can't click through to that article -- when I dismiss the pop-up, the tantalizing "Climate Shock" headline disappears.

I do say that all humans require energy to survive, and more efficient forms of energy require capital in the hands of innovators.

I'll be happy to read the article if you can give me a link that functions better for me.

fexlon What's Really Warming the World?

Are there any data on water vapor concentrations? I ask that because I have read that the contribution of water vapor to the greenhouse effect is perhaps two to four times greater than CO2.

fexlon What's Really Warming the World?

Likely yes, but please be careful that the remedies do not cause more severe difficulties than the problem itself.

fexlon What's Really Warming the World?

Sorry I deleted my comment out from under your feet. He was responding to my exclamation about the large spike upward in CO2 levels on that first graph on the EPA site. After posting it, I deleted it because I answered my own question.

fexlon What's Really Warming the World?

http://www.ncdc.noaa.gov/paleo/globalwarming/temperature-cha...

There you can see a strong correlation between CO2 levels and temperature going back nearly half a million years. Teasing out cause and effect is the interesting task.

fexlon Why do buses bunch?

It's bizarre that it would be illegal. For all I know, it might be illegal in Peru too, but it happens, and it works pretty well.

In Lima, the spotters are known as "dateros" (loosely, "data wrangler"). The bus drivers pay them roughly 20 centavos, I think per stop but I'm not certain.

One case where it doesn't work is when certain bus drivers ignore the system and aggressively jump ahead of other buses. Nevertheless, it's pretty smooth.

fexlon Why do buses bunch?

In Lima Peru the bus drivers pay spotters on the street who report flow conditions by cell phone.

fexlon Negative Interest Rates May Spark Existential Crisis for Cash

Yes, you're talking about 4.7 cubic feet of gold there. Buy the island and then you'll have a place to store 1 cubic foot of gold, to pay your routine expenses.

fexlon Negative Interest Rates May Spark Existential Crisis for Cash

Some have already closed that exit, banning the storage of cash in their boxes. They want to keep your funds available for negative interest rates and possible bail-ins.

fexlon Hungary plans new tax on Internet traffic

Not only that, they took a lot of money in exchange for that "free" eduction -- often from people who didn't even use the service. So no, they don't have a "stake" in the products of anyone's mind. That's repugnant.

fexlon Unsung Geniuses

I sing the praise of the rarely mentioned genius Moses Schönfinkel, who invented combinatorial logic.

fexlon Peru: The Future of Gastronomy

We traveled to Lima a few years ago, and the variety and quality of the food in the grocery stores and restaurants was astounding. For the equivalent of 2 to 5 bucks, you could get a lunch that would cost easily six times that in the U.S. -- if you could find anything equivalent.

fexlon The Y Combinator (no, not that one) – A Crash Course on Lambda Calculus

OK, I went ahead and revived the "==" syntax for recursive definitions, so you don't have to use '@' (fixpoint) explicitly.

https://github.com/chkoreff/Fexl/commit/57b841cb6c2347cad147...

fexlon The Y Combinator (no, not that one) – A Crash Course on Lambda Calculus

Postscript: You might well ask why not just use "=" only, and assume that all definitions are potentially self-referencing?

That's a non-starter because I find that redefinition is the more common intent:

    \x=4
    \x=(* x 5)
    \x=(+ y x)

In those cases I don't want x defined in terms of itself, but rather in terms of the previous definition of x.

That is why I would insist on a special token such as "==" to express the intention of self-reference.

fexlon The Y Combinator (no, not that one) – A Crash Course on Lambda Calculus

True, I could implement it in terms of direct self-reference. At one point I used the "==" syntax for just that purpose:

    \append==(\x\y x y \h\t [h; append t y])

Maybe I should resurrect that syntax option. :)

It was trivial to implement. When the parser sees the "==", it just automatically abstracts the symbol "append" from the definition and applies the fixpoint operator (Y combinator).

The only reason I eliminated "==" in the first place was that I was in the throes of using different syntaxes for lazy, eager, and self-referencing definitions. Now I've settled in on "=" always meaning eager evaluation, without exception. Then I got hyper-minimalist and said that's it, there's only one syntax for definitions, and it's "=", and if you want self-reference, use "@".

However, the decision to settle in on eager evaluation now frees up "==" once again as an option for self-reference. So I may bring that back.

Thanks for the food for thought.

fexlon The Y Combinator (no, not that one) – A Crash Course on Lambda Calculus

I do use it directly. For example in Fexl I define the append function for lists as:

    \append=(@\append\x\y x y \h\t [h; append t y])

Where '@' is the Y-combinator.

Note that there's no direct self-reference with the symbol "append" there. I could define it equivalently as:

    \append=(@\loop\x\y x y \h\t [h; loop t y])

fexlon Fexl – Highly robust functional evaluation

Fexl is a functional programming language. I used the term "functional evaluation" because Fexl evaluates functions.

Here are a few code samples:

http://rosettacode.org/wiki/99_Bottles_of_Beer#Fexl

http://rosettacode.org/wiki/Fibonacci_sequence#Fexl

http://fexl.com/sample/

This one's a bit more involved:

http://fexl.com/demo/

You'll also find some code samples in the "test" directory:

https://github.com/chkoreff/Fexl/tree/master/src/test

The program a1.fxl there is the definitive test suite. The program a2.fxl reads what you type and echoes it back.

The samples above should help illustrate the nature of the language. Grammatically, it's very simple:

http://fexl.com/grammar/

For another quick illustration of the language, I'll give you a sample here:

    say "Hello"
    \x=(* 4.7 8.6)
    put "x = " put x nl

The output is:

    Hello
    x = 40.42

fexlon Fexl – Highly robust functional evaluation

This version handles syntax errors, out of memory errors, and out of time errors, propagating them upward instead of halting with an error message, and reporting them in an orderly fashion at the end of the main program. Now the only calls to "die" are those which should never happen, i.e. they are pure assertions which are never expected to fail.

This allows for some very nice embedded calls to parsing and evaluation from within a Fexl program itself, which can always be expected to return to the caller instead of halting.

Ultimately I'm going to put a full-powered interpreter right on the web to allow arbitrary programs submitted from strangers, and this release is a necessary prerequisite for that.

fexlon Star Trek 1971 Text Game (2008)

Same here -- I played it in 1974 on an HP 2000F minicomputer via a teletype located in a converted janitor's closet at my high school.

The author mentions the lack of ability to renumber the lines in a BASIC program, but I'm quite sure there was a RENUM command that would do that.

In 1976 we got ADS (CRT) terminals in the computer lab, and once I figured out ESC-sequences, I had a shoot-em-up space ship game going. God I wish I still had the source code for that. :(

fexlon Heartbleed vulnerability tester

I see a funny thing when I test it against yahoo.com:

  $ ./Heartbleed yahoo.com:443
  (bunch of returned bytes)
  2014/04/08 12:59:46 yahoo.com:443 - VULNERABLE

Near the front of the returned bytes is the sequence "yheartbleed.filippo.ioYELLOW SUBMARINE". That is some padding buried inside the Heartbleed source code.

I assume that the returned bytes are a peek inside the memory of a yahoo.com server, and we can see the padding supplied by Heartbleed, followed by some more bytes that depend on the server state.

Am I interpreting that correctly?

fexlon Range-Checks and Recklessness

No it's a good point actually, and it pays to know your context. Frankly, looking at the 118 lines in assert.h, it does considerably more than I really need.

Instead of this:

  assert(buf->pos < buf->str->len);

I could just do this instead:

  if (buf->pos >= buf->str->len) die("bad pos");

If the die message is unique, I don't really need to include __FILE__, __LINE__, and the expression itself in it.

I could even do this, though it's probably overkill for something that should never happen anyway:

  if (buf->pos >= buf->str->len)
      die("bad pos %d %d", buf->pos, buf->str->len);

fexlon Range-Checks and Recklessness

Right now, in my code, assert(0==1) produces this output to stderr:

  run: run.c:422: main: Assertion `0==1' failed.
  Aborted

That is what I want.

You are correct. If I build with -DNDEBUG=1, then the assert is completely ignored: no error message, and no abort. That is not what I want. Therefore I will not build with -DNDEBUG=1.

I will certainly not introduce "logging to a file" as a concept inside buf.c. There is no need for the pure data manipulation code in buf.c to know anything about files or stdio, or a specific name of a log file.

If the assert from assert.h does not do what I want, then I'll make a version that does. However, that is a moot point, since right now it does what I want.

fexlon Range-Checks and Recklessness

Assertion failure messages are sent to stderr. Production code can capture that as it wishes.