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F (2006) (nsl.com)
175 points by tosh on Aug 21, 2020 | hide | past | favorite | 56 comments


In a somewhat similar vein, I made a concatenative array language inspired by kdb+/q: https://cryptm.org/xs/

Unlike other concatenative languages, the order of operation is right to left, and it supports infix operators. This gives the language a very conventional array language feel, while also giving you the power and flexibility of the stack.

As far as I'm aware, there's really nothing like it. Would love if someone gave it a try!

Here's an example, the factorial function:

  xs> fac:(prod 1+til);
  xs> fac 4
  0: 24
You can also define new infix operators:

  xs> add:{+.};
  xs> 3 add 2
  0: 5
Here's an example of generating a sequence of values, where n_t=n_{t-1}/2:

  xs> (x:;x%2) fixes 12
  0: [12 6 3 1 0]
Note how when we reach the fixpoint of zero, the recursion stops. These kinds of implicitly recursive combinators are very powerful. Also, equality on floats is not strict, so we can also do this with floats, without having to worry about small differences in precision. This is useful when working with equation optimizers and root finding methods.


looks cool, like the ideal language I would like to write

for boosting popularity:

1- would be nice to use in tryit online or repl.it

2- would be nice to have a link to the implementation repo in the docs

3- have you tried winning some golfscript contests on stack overflow?

4- main improvements over K, with small code samples?


I do have some examples in the examples section. There's a link to the OCaml implementation on the page as well. A repl.it would be awesome, I'll definitely do that.

I hadn't heard of golfscript, but those would make some really great examples. I do have a couple Advent of Code 2019 solutions though.

Thanks!


Did this jump to the top because the click target for the link is so small that people are accidentally upvoting it?


Probably, I accidentally upvoted it too.


This is a very thought provoking language, thank you.

off topic, is it just me? Or a thing informed by silly memes to see this letter and immediately think oh man, Rest in Peace?!



More on topic : it might make sense to retitle as “F (loopless programming language)”


Yeah, I thought someone had died.


It is often said that K can beat the speed of C for some tasks.

The name of this site is "nsl" for No Stinking Loops.

Here is an array programming challenge for the K programmers reading this thread.

There are two large files A and B.

   File A
   AAAbjhOJxxxWXrCHt
   AAAsofxxxLqKbYOAwLMHG
   AAACgxxxOea
   AAAwfHjDtoJc
   AAAiCfYnbVXWhuvtEx
   AAAkzzQwvf
   AAAdjLalKFapoYAcGE
   AAAthGazmnfK
   etc.

   File B
   AAAwfHjDtoJc
   AAAbjhOJxxxWXrCHt
   AAAiCfYnbVXWhuvtEx
   AAACgxxxOea
   AAAkzzQwvf
   etc.
The task is:

What are the lines in B that are not in A?

Something like

   grep -vf B A
But without the stinking loops!

EDIT: File A,B formatting


In J (which might be slower than K) with excessive comments for a one-liner:

    echo@> (2{ARGV) -.&([: <;._1 LF, 1!:1) (3{ARGV)
    NB.    2nd arg                          3rd arg
    NB.              g&f execute f for each, then g on both
    NB.                              1!:1 read file
    NB.                          LF, prepend newline
    NB.                 [: <;._1 split based on first char
    NB.             -.  remove right elements from left array
    NB. echo@> echo each line
    exit 0
On two ~1.6MB files with ~15k lines (both the same except 3) I had lying around:

    $ time j9 -c ./pseudo_grep.ijs test_b test_a
    …
    real   0m0.064s
    user   0m0.032s
    sys    0m0.017s
    $ time grep -vf test_b test_a
    …
    real   0m5.815s
    user   0m5.234s
    sys    0m0.576s
Note that most of the script is for loading each file into an array of lines. Most work is done by -. on the two arrays, which is exactly what you asked for, e.g. 0 1 2 3 4 -. 2 4 is 0 1 3. https://code.jsoftware.com/wiki/Vocabulary/minusdot#dyadic


In loopless Python:

    set(open('file_b')) - set(open('file_a'))
Slower than J by a factor of 2-3, but still 10x faster than grep:

    real    0m0.128s
    user    0m0.078s
    sys     0m0.063s
This would make a good Rosetta Code prompt.


I didn't know you could simply open a file and setify it. Interesting. & neat.


You can setify any iterable. File handles are iterables that return a line at a time. Tada!


> File handles are iterables...

I did not know that. Assumed you had to somehow wrap them first. Very useful, thanks!


this is cheeky, I like it


This is only fast because it hits C underneath, isn't it?


That grep is not doing the same thing as the code, nor necessarily what the exercise requires. By default, grep tests patterns, so it's turning all those entries into individual regular expressions. You want to use fgrep, or the -F flag to make it treat all the source matches as fixes strings.

In my simple test, that resulting in grep running in 44% of the prior amount of time it required (still more than python though).


Apologies for the careless omission. I tested the difference on a larger job; with grep 28s, with fgrep 22s.


I think theres probably a sweet spot in how large the files are compared to the method used, because eventually disk access may dominate the running time. Putting files on a ram disk (/dev/shm on some distros) would help.

I tested with files just over 2 MB on a small Digital Ocean VM. Depending on disk speed, based on running time I suspect you ran on files at least an order of magnitude larger. What time did python run in for those? Seeing memory usage from time might be illuminating for these tasks too. Using 4x the disk size in memory is fine for a couple MB file, but less so for a couple GB file (in which case creating a bloom filter or trie might be better, but I really have no idea if Pythons set functions do that already).


In Dyalog APL, which isn't K:

          A←⊃⎕nget 'C:\test\a.txt' 1
          B←⊃⎕nget 'C:\test\b.txt' 1
          A~B
    ┌─────────────────────┬──────────────────┬────────────┐
    │AAAsofxxxLqKbYOAwLMHG│AAAdjLalKFapoYAcGE│AAAthGazmnfK│
    └─────────────────────┴──────────────────┴────────────┘
Read each file as a nested vector of lines. A without B, like set operations.


i'm not drinking this kool-aid. you're in a strange place if you think it's loops that are the cause of software complexity.


Loops are 100% the worst offenders of software complexity. Loops and tail recursion are the most powerful constructs we have, and are too powerful for the vast majority of problems. When using the principle of least power you find that a loop or tail recursive function is exceptionally rare.


They might be a great source of algorithmic complexity, but I would argue that by far the most part of software complexity is architectural, not algorithmic.


When you can reduce the amount of code you have to write by 100x, architecture no longer becomes important. When all programs are so short, they become very cheap. And when they become cheap, they are easy to replace and rewrite. At this point, architecture becomes irrelevant because you've removed all abstractions in the first place.

If the components of your company's system never are longer than a page or two of code, rewrites become trivial, making planning for the future unnecessary. This is the real promise and value of array languages.

Or put more simply, the size of a code base is the dominant factor in its complexity. Less code is less complex code, is better code.

Also, loops imply mutation, which is the second biggest indicator of complexity. Mutation kills code bases and kills projects. When you decide to never use a loop and to never mutate, you're on the right path. Now the next step is to try and remove as many lines of code as humanly possible.

A good way to measure how you're doing is by comparing the size of your gzipped (or zipped or whatever) codebase to its uncompressed form. If they are close in size, you know you are on the right track. Or in other words, you want the size of your code base to be close to its Kolmogorov complexity.


Less code to write, less code to read, less code to maintain, executes faster[1]. What's not to like?

What about someone who thinks "if" is a big source of software complexity? https://www.youtube.com/watch?v=z43bmaMwagI - talk is "If considered harmful: How to eradicate 95% of all your bugs in one simple step - Jules May".

[1] in interpreted languages, anything you can push down for the runtime to do instead of writing that same code in the interpreted language, tends to execute faster. e.g. my_string.count('c') in Python compared to a `for` loop over the characters written in Python.


The traditional unix command for this is 'comm' and it is usually installed by default.


How would you solve this task with comm?

For that sort of comparison I usually use

   diff -y A B


    comm -13 A B


I totally screwed up the example. I wanted list B to have some items not in A, e.g.,

   echo AAA_not_in_A_xxx >> B

   fgrep -vf A B
Result should be

    AAA_not_in_B_xxx


In k9 it should be:

    A_B


     `A 0: ("some";"lines";"are";"here");     / write to file A
     `B 0: ("more";"lines";"follow";"here");  / write to file B
     _/ 0:' `A`B                              / read files A, B and find lines of B that are not in A
    more  
    follow


Ok, I'll bite:

Can someone ELI5 what this is about, why it's interesting, and why someone would want to learn or use this language?

(I'm coming from the perspective of someone who builds user-facing web & mobile applications in Ruby, Crystal, Python, JavaScript, Swift, etc.)

BTW - I'm asking not because I doubt there are good answers to any of those questions - but because I truly don't understand and wish to.

I read the opening paragraph and without spending an hour looking up the definition of each term, I'm more confused than when I started :)

Thank you in advance!


I've no experience with this language or it's genre of languages, but I doubt there is a good answer for you.

You're working in a very different space (business oriented, needs networking protocols, probably no major number crunching, your collection of languages do fine for your job etc.)

Some languages are just explorations of the language space, disjoint from your language-using space therefore irrelevant to you directly, and may be (currently) only of academic interest. I'd learn this if I had time, to understand different paradigms, and for fun. Sometimes this is useful. Sometimes not.


Thank you! That’s helpful. I had a hunch this was focused on theory / academia, and if that’s the case, that makes more sense.



implementation (also of g and h):

http://www.nsl.com/k/f/

(via comments from 2015)


> There are no side-effects

Yet it prints stuff to the terminal.


I don't know how F is implemented but in a lot of stack languages printing to the terminal isn't really a side effect. Every function takes the state of the entire world as it's one and only parameter and returns a new world.


Also heats up the room.


Exactly. If the program won't read it (the printout) back, or unless it is designed specifically to sense the heat, then, strictly speaking, it's not a side effect (in the particular sense in which a side effect may reflect on the program execution).


It also uses up RAM.


Ha! Well deserved but how did this pop up to #1? All of nsl is a great show of what you kan do with k, an apl.


I think we have a new champion in the unofficial HN useless-headline contest.



Yet another link to click on? I don't come to HN to work!


not labour but leisure: compare https://en.wiktionary.org/wiki/σχολή


Press F for respects.


People probably think this is what article about.


I've periodically thought I should at some point learn all the single-letter programming languages. Have we covered the whole alphabet yet?


At least the English alphabet has been covered: https://beza1e1.tuxen.de/one_letter_proglangs.html


The N programming language (1990?) is spookily reminiscent of PyTorch!

> Expecting a wide use of neural network algorithms in the near future, our objective is to get a complete software development environment for programming and testing new applications. We intend to produce a high level language for neural network specification, as a part of such an environment.

> The language we propose is characterized by a high degree of modularity, based on parameterizable data structures, with functionalities in the form of update methods attached to them. Composition rules of structures and methods enable to build, step by step, more complex structures from smaller ones previously defined. Objects are viewed as autonomous modules which are linked through plugs for communications. We particularly cared for the parallelization of methods running concurrently on different objects of the network. The syntax is largely related to those of the C and C++ languages.

https://link.springer.com/chapter/10.1007/978-3-642-76153-9_...


F from this topic is not in that list.

M omits the language also known as MUMPS, and also there was a second .Net based language informally called M#, apparently developed by Microsoft Research as part of Midori project, and called "C# for Systems Programming" in public communications from the developers.


superbly interesting read


great list!


I would be shocked if there were any single letters remaining unused for programming languages. We reached <letter>FS saturation for filesystems many years ago, after all.




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