What is XXL?

XXL is a new programming language whose goals are simplicity, power, and speed. We throw out most of conventional programming language thinking in order to attain these goals.

Status

Passes tests. Useful for writing small utilities, for me.

Ideas valid, but development stalled pending rethink of virtual machine. The current VM leaks memory during complex operations and is generally too slow. A more modular type system would be nice as well.

Tested so far on Linux (64bit x86 & GCC or Clang), OS X (Clang), Windows (Cygwin64), Android under termux, Intel Edison and Raspberry Pi. Should work on iOS as well but untested.

Examples

Manipulate variables

In XXL, we call functions verbs, and they can have only one or two arguments (named x and y).

You call a verb like x func or x func y.

Code reads left to right. There is no order of operations. Semicolons are important. Comments are // to end of line.

Aside from the poorly documented built-in verbs, there isn't much to learn in terms of syntax.

When you name variables, you specify their names as a special name starting with ', and use the as or is verb. Afterward you refer to them without the '.

(Note: the 0. and 1. below are part of the XXL interactive prompt.)

0. 41,6,2 as 'ages     // create a variable named ages with "as"
(41,6,2)
1. 'ages is (41,6,2)   // equivalent to the above, reverse order with "is"
(41,6,2)
2. ages
(41,6,2)
3. 'ages is 41,6,2     // WRONG! there is no order of operations - group with ()
(41,6,2)
4. ages                
41                     // oops..
5. ages; 666           // semicolons separate expressions
666                    // repl shows you result of last expr

XXL is functional, so you don't use any loops to manipulate values:

3. ages each {x * 2}
(82,12,4)
4. ages each {x str," years old"} join "\n"      // join into separate lines
"41 years old\n6 years old\n2 years old\n"

(Note: \n is nerd speak for newline or linebreak in the terminal)

To save time, XXL has the questionable feature of allowing you to omit the x part of the very beginning of a function. You'll often see this pattern employed for brevity in the examples below. Examples:

3. ages each {x * 2}
(82,12,4)
4. ages each {* 2}
(82,12,4)
5. ages each {x str," years old"} join "\n"
"41 years old\n6 years old\n2 years old"
6. ages each {str," years old"} join "\n"
"41 years old\n6 years old\n2 years old"

each is a regular function (verb), believe it or not. It happens to understand what to do given a list (vector) on the left side and a function on the right. In contrast to most languages, XXL doesn't really have any syntax that defines looping abilities. It's all just regular XXL functions.

Quasi-JSON encoder

Not really to spec, but what is? About 6 lines of code, without the tests:

Here's what's going on in this monster. I'll explain the parts, and then the sequence of how it comes together.

// (e)nclose (c)urly(b)races, (s)quare(b)brackets, (q)uotes:
'ecb is {"{",x,"}"}; 'esb is {"[",x,"]"}; 'eq is {"\"",x,"\""}; 

Line 1: Define three functions to enclose values in the typical JSON delimeters. ecb/esb/eq enclose their argument in curly braces, square braces, or quotes, respectively. They use the name x to refer to their argument.

'jc is {join ","}; 'jac is {each y jc};  // join x with commas; apply y to each of x then join with commas

Line 2: jc (join comma) joins the contents of its argument together with a comma in between each item. jac does the same thing, but after first calling its right argument (y) on each item - jac here is a mnemonic for "join and call".

The astute might notice that jc and jac don't refer tox, because the first verb inside a function will be invoked automatically with x as the left argument. In small functions, x is almost always the first term in the function's code, so being able to omit it results in some expressivity. More on this later.

'pair is {encode,":",(y encode)};        // key:val pair for dict

Line 3: pair calls another function, encode (which we define later), without referring to x. It then appends a : to the string that is returned from encode, and then appends that to the result of calling encode with the y argument. This is a form of recursion.

'dict is {key as 'k; x val as 'v; [k],v >: pair jc ecb}; // get keys/vals, pair merge, commas, braces

Line 4: dict takes a dictionary as an argument, gets its keys as a list using the built-in key verb, and saves them in a new variable called k. The values of the dictionary (also a list) are extracted using the built-in val verb and become v.

These two lists then become the left and right arguments for successive calls to jc using the "each pair" or >: verb. Each of the key/value pairs will get commas between them. Then, we enclose the whole of the dictionary in curly braces, like {"name":"Tyler","age":"2"}.

All the looping verbs have short names that end in :.

'many is {as 'el type case ('char, {el str eq}, 'dict, {el dict}, {el jac encode esb})};

Line 5: many isn't as grody as it looks. Its purpose is to handle multiple-item collections (called vectors in XXL). In our case, we have to worry about two main ones: character vectors (strings) and dictionaries.

First, we store the value of x as el (element). Then we extract the value's type using the type verb, and then use the case verb to decide how to treat all the different types.

x case (y0, f0, y0, f0, ..., else0) will check x against each of the y values; if it matches, the corresponding function f will be invoked with x as its argument. If none match, x else0 will be invoked.

If it's a character vector (a string), we pass el through the str verb to remove its tag (a feature we'll explain later).

If it's a dictionary, we call our dict function.

If it's anything else, we recurse by calling encode again, and then enclose the result in square braces (think arrays of numbers).

'encode is {ravel[many,str]};            // ravel calls x y[0] for arrays (len > 1), x y[1] for scalars

Line 6: And finally the star of the show, encode. ravel is a verb that allows you to take one branch of logic for single-item values (like the number 3), or a different branch for values that have many items, like an array or string (vector of char). Depending on the type of x, encode will dispatch either many (for multiple values) or str (for simple, single values).

MySQL Slow Query Watcher

Here we use command-line MySQL to get process list, turn into table, find interesting slow queries.

Note that the 0., 1. etc is XXL's prompt in interactive mode. The number you see next to the prompt allows you to refer later to that line of input or the result XXL produced for it. Don't type this part, or the comments, at the interactive REPL.

0. 'slowtime is 2;
// get output, split it by line, then by column, save
1. "mysql -e \"show full processlist\" --batch" Shell.get split "\n" each {split "\t"} as 'lines; 
// the first line is column headings, massage data for each row, create table with keys:data
2. lines first each {make '} : (lines behead curtail each {make "issstiss"}) as 'procs;
// Use  except  with an anonymous function to filter rows we don't care about
3. procs except {@'Time<slowtime | (x@'State="")}
['Id:194128i, 'User:"destructoid", 'Host:"localhost", 'db:"destructoid", 'Command:'Execute, 
  'Time:3i, 'State:"Sending data", 'Info:"SELECT * from ... "]

Originally used as a one-liner to fix a performance issue on a site.

Simple Web Server (Counter)

Here's an example web server application that acts as a counter.

You can run this as./c examples/web-ctr.xxl.

XXL doesn't include HTTP support explicitly (yet), so this server speaks a little HTTP. Source code in full:

0 as 'ctr;

'make_http_response is {
	[
		"HTTP/1.0 200 OK",
		"Content-Type: text/plain",
		"Connection: close",
		"Server: xxl v0.0"
	] show as 'template;
	template join "\r\n",
	"\r\n", "\r\n",
	x,
	"\r\n", "\r\n"
	flat
};

(8080,"localhost") Net.bind {
	ctr + 1 as '.ctr repr make_http_response
}

(We didn't show the XXL prompt here, just the code itself.)

This simple server uses (socket_options) Net.bind (handler) to start a listening network connection and setup a callback.

When invoked, the callback fetches the value of ctr (a global), adds 1 to it, resets the global (as allows you to assign in other contexts - like globally here with '.ctr), convert that number to a string (repr), and then create a somewhat-valid HTTP response with that string.

make_http_response basically construct a simple string from your output, flattens the list, and returns it to Net.bind to send.

Docs

Here's some useful info, but no real docs yet.

• Groceries tutorial - a short tutorial written for non-programmers.

• Mailboxes soliloquy. Mailboxes are like a message queue and allow your program to use multiple threads.

• Posts are a general concept for sharing data between XXL and the outside world. Work in progress!

• List of verbs in XXL, represented as an XXL table

• Working with files

• Notes about logic

• Implementation notes

See the various tests for more examples. In particular, you may appreciate test-logic.h, and test-semantics.h.

Philosophy

• Terse. It is much better to express yourself clearly in a few words rather than many. We provide powerful operators that allow you to do more while describing less.

• Accessible. XXL avoids niche-y programmer terms like "map" and "reduce" in favor of common English

• Minimalistic, but not spare. Provide tools people commonly need, even if they're a bit duplicative of other, more primitive approaches.

• Fast. XXL cares deeply about performance, for the same reason a person should care about the quality of any tool they use for professional work.

• Tangible. Abstractions provided by many systems and platforms make it much harder to reason about what your program is doing. XXL just helps you program the computer in the way the computer wants to be programmed. Those with a background in assembly might see some familiar tones in XXL.

These goals have not yet been attained.

Motivation

I need a swiss army knife for data manipulation with predictable performance and concise syntax. I want to use some of the more exotic features I've tasted in other languages, but not all of them. In particular, I feel like programming has gotten a little too stack- heavy.

Features

Minimal, easy to grasp syntax

XXL may seem odd at first glance but it's much simpler than other languages which suffer from complex grammars, rules, and special cases. You don't have to understand APL, K/Q or even functional programming to use XXL.

Clean, very easy to understand and parse left-to-right syntax with only three special forms: comments, strings, and grouping (i.e., ( ), [ ] and { }).

Everything else is either a noun or a verb. Learn the verbs and you know the language.

Values and variables are called nouns. The first time you create a noun, you usually refer to it using a tag: 'z is 1. You can use as if you want to build up an expression and save it: 1,2,3+1 as 'numbers.

If you didn't use a tag name (like 'numbers) and instead just wrote numbers, XXL would try to find an existing noun named numbers, and insert the contents of that instead, which probably isn't what you want.

Verbs are either postfix (also called unary: having one variable, called x): 1,2,3 len or infix (binary: two variables, called x and y) 1,2,3 + (4,5,6).

Verbs work with the things immediately to the left or left and right. There is no grouping or precedence. This is much easier to keep track of mentally and allows you to much easily scan code. Use (), [], or {} to group values if you must, but many times you can write long expressions with few groupings.

There is nothing special about len, or +, or any of the built-in verbs. They are simply verbs that have been created for you already. You can create your own system-level verbs or replace ones that already exist.

You can create nouns in the middle of expressions and refer to them later, such as this in this tedious example: 1,2,3+2 as 'num + num

Agnostic about whitespace. Don't let invisible special characters ruin your day.

Trees

We don't yet have a full tree data type yet, but operations on list-of-lists are pretty diverse. After all, XXL is written in terms of its own verbs and values.

x nest [open,close] creates sublists in x between matching open and close tags. Create parsers like an animal.

Note: In the examples below, 0., 1., etc are the XXL command line prompt. Abridged output shown on the line below.

0. 1,4,4,0,5,5,6 nest [4,5]
[1i, [4i, (4,0,5i), 5i], 6i]

x ravel [funmany, funone] calls funone if x is scalar, funmany otherwise. Pair with self to recurse. A napkin sketch of a markdown parser:

0. 'body is {behead curtail};
1. 'mdtxt is "My *Markdown* parser";
2. 'html is ['b:{"<b>",x,"</b>"}]; // define some formatting templates
3. mdtxt nest ["*","*"] :: {ravel [{x body html.b},str]} flat
"My <b>Markdown</b> parser"

The contents of the html callbacks, the nest control parameters, are all just data that you can build up or pull in from anywhere. Compare with traditional control structures used to manipulate data which exist inside the source code only and are not mutable at runtime.

Or use deep and wide for more explicit macro-control of recursion.

Erlang-inspired mailboxes

Thread safe for both readers and writers (at some cost to performance of course). Fast enough to be usable for basic purposes (800 request/reply cycles a second on a $5 Digital Ocean box).

0. [] Mbox.new as 'myservice;
1. myservice Mbox.watch {x show}
2. myservice Mbox.send 55;
55

watch spawns a thread to act on mailbox messages. The 55 seen here is from the show statement in the lambda. A y variable is available inside the callback to maintain state; it starts as [] and it set to whatever your function returns.

See doc/sect_mbox.xxl for more.

Files

The File namespace contains file-related stuff. Let's explore:

0. File
['basename:'1(...), 'cwd:'1(...), 'dirname:'1(...), 'get:'1(...), 'ls:'1(...), 'path:'1(...), 'set:'2(...)]

[] File.cwd tells you the current working directory:

1. [] File.cwd
"/mnt/tlack/work/xxl"

Note: Here we use [] as a placeholder because cwd doesn't take any arguments.

fname File.dirname strips the last component off a name.

2. [] File.cwd File.dirname
"/mnt/tlack/work/"

pattern File.ls shows you what's in a folder:

3. [] File.cwd,"/*.c" File.ls
["/mnt/tlack/work/net.c", "/mnt/tlack/work/repl.c", ....]

data File.set fname sets the contents of file fname to data, which must be a string (vector of char). It returns the data so you can continue using it in your expression.

4. "Hello world!" File.set "test.txt"
"Hello world!"

fname File.get reads and returns the contents of fname as a char vector.

5. "test.txt" File.get
"Hello world!"

pathpartslist File.path converts from lists of filename parts to actual platform-specific paths.

6. ["mnt","tlack","work","xxl"] File.path
inputs@0: ["mnt","tlack","work","xxl"] File.path
outputs@0:
"mnt/tlack/work/xxl"

Tables

Well, the beginnings of them anyway.

0. "name,age,job\nBob,30,Programmer\nJane,25,CFO\nTyler,2,Dinosaur Hunter" as 'data;
1. data split "\n" each {split ","} as 'fields;     // in a fantasy world where csv is never escaped
2. fields first:(fields behead) as 'emp             // : creates dicts or tables 
["name", "age", "job"]:[
["Bob", "30", "Programmer"],
["Jane", "25", "CFO"],
["Tyler", "2", "Dinosaur Hunter"]]

This is similar to the MySQL example above in that we are unpacking data and making a table out of it.

Notice that the printed representation of the table is similar to what you'd type in to regenerate it.

The in-memory table works very much like a regular value, and you can join it with more dictionaries to append rows with , as you'd expect.

3. emp,["name":"Steve","age":"42","job":"Fact Checker"]
["name", "age", "job"]:[
["Bob", "30", "Programmer"],
["Jane", "25", "CFO"],
["Tyler", "2", "Dinosaur Hunter"],
["Steve", "42", "Fact Checker"]]

Or join it with a list that has a value for each column:

4. emp,["Arca","2","Tiny Dog"]
["name", "age", "job"]:[
["Bob", "30", "Programmer"],
["Jane", "25", "CFO"],
["Tyler", "2", "Dinosaur Hunter"],
["Arca", "2", "Tiny Dog"]]

Notice that we did not save the result of expression 3 (where we joined emp with a dictionary containing Steve's record) so the change was not saved to emp. Like most verbs in XXL, , does not modify the x argument, it creates and returns a new value. Looks like Steve is going to have to check someone else's facts from here on out.

Use amend (or equivalent the short operator !) to update emp in place. emp![["age"],{::{base 10}}] would convert the ages to numbers so you can ruthlessly compute them. In this example, "age" has to be put into a list here because otherwise it would think you want to update three indices - "a", "g", and "e".

Get individual rows with emp@0 or 0,2 from emp, or rows with "age" from emp or emp@"age" or, if the key "age" was a tag like 'age, you could use simply emp.age.

Search for matching values using match (or ~) or filter rows with {..} from emp or emp except {..}.

Still no joins, many rough edges, untested performance.

Other

• Variable names can't contain numbers, so you can build up some pretty clean and short expressions that mirror mathematics. 3u b5 means 3 u b 5, or b(u(3),5), assuming u is a single argument (unary) function and b is a two argument (binary) function. If you're recoiling in horror right now at losing your precious numerals in variable names, consider how often you're just poorly naming a temp variable.

• Variable names can contain ?, so you can name your predicate functions in a pleasant manner.

• Values can have "tags" associated with them, allowing you to create an OOP-like concept of structure within data, while all regular operations work seamlessly as if you were using the underlying data type. Consider the classic OOP example of a "point", which in XXL would just be a tagged int vector like 'point#(100,150).

• Vector-oriented and convenient manipulation on primitive values. For instance, 1,2,3 * (4,5,6) is perfectly legal and returns 4,10,18. This is a huge time saver and eliminates many loops. It's also pretty fast, which somewhat makes up for the dangerously slow interpreter.

• Diverse integer type options, including 128bit octaword (1 make 'octa). At this time we don't display the int type when displaying the representation of the numeric value. Use the x type verb to discovere what size of int you are working with.

• Fast-enough unboxed binary data files. 25 million int/s to disk per second on $5/mo Digital Ocean droplet via 1024*1024*50 count Xd.set "/tmp/50m.xd"

• Threading support, kinda. XXL has the notion of threads available internally, but the only way they are usable from inside XXL code is via mb Mbox.watch {..}. This is because modifications to contexts' data items are not locked or synchronized, So chaos will surely ensue if you modify global data from threads. Thus, the mailbox acts as both a safe communication mechanism for threads, and a way to discourage global state mutation. See doc/sect_mbox.xxl for more.

• Built in simple networking. Client-speaks-first protocols are a snap to implement. World's easiest echo server: [8888,""]Net.bind{"Echo: ",x}. Net.bind creates one thread to service each port/service.

• Vim syntax file in tools/syntax/vim-syntax.vim (which is generated by vim-build.xxl in that same directory).

• No stinkin loops (and no linked lists, either)

• Supports \\ to exit the REPL, as god intended (quit and exit too)

• BSD license

Not yet implemented

XXL is still very much a work in progress and is mostly broken. That said, here are the major features I anticipate finishing soon-ish.

• Currently has severe memory leaks and performance problems
• Floats! We've got floats now - no comparison tolerance yet tho.
• Dictionary literals (dictionaries do work and exist as a primitive type, just can't decide on a literal syntax for them) Settled on and implemented ['a:1,'b:2] by creating : as the make-dict operator and making , smart about dicts.
• JSON
• FancyRepl(tm)
• Dates/times (need to figure out core representation and a way to express them as literals in code..)
• In-memory tables Few operations yet, and bugs remain, but the notion of tables has slowly seeped in. See tests.
• ~~Non-pointer tags implementation to avoid logic to enc/decode to binary for disk and IPC~ Temporarily replaced tag representation with 128bit pointer string. Fast to compare, almost as fast as possible to create (memcpy), zero overhead on IPC ingest/excrete, not terribly large on today's memory sizes.
• I/O (files, sockets, mmap)
• Logged updates (I like Kdb's approach to this)
• Mailboxes/processes (implemented as a writer-blocks general list) Available in "Mbox" class.
• Streams, laziness (perhaps based on mailboxes? studying other systems now)
• Tail call optimization in functions using the self keyword as per Kuc's approach
• Sorted vectors
• Grouped/index types
• Well-supported Apter trees (see also APL's approach).

Well known bugs

Work in progress on these:

• Interpreter speed and memory leaks. These are at times severe.

• The interpreter still recurses too much in some scenarios, even though its main loop is self-managed on the heap. C call stack depth gets too deep. I have a simple plan to resolve this, but it requires a (much needed) rewrite to applyexpr(), which can be thought of as the interpreter loop.

• The join verb (,) is still finnicky about joining like-types of data with general lists. In particular, I often find myself a bit puzzled by results like ['a,2],3 - should this be a two-item list with two items in the first sublist, or a three element list? Before you answer, consider ['a,2] as 'q;q,3. When in doubt, build parts separately and combine.

• You can't name a variable you define x or y, since the interpreter treats those specially. There's no real reason for this other than the idea that it's faster to resolve this short literal symbol manually using what we know about the calling frame, rather than setting it as a regular variable in the dictionary that is used by the context to resolve symbols. The setting part works, it's just resolving x afterward doesn't consider the dictionary.

Open questions

• Date and time stamps: Nanosecond precision from uint64 sufficient? What about literal representation? Can we use 1997.12.31.09.31.45.333 or something non-pollutey like that? Need to patch up apply() to allow you to index 'day and similar.

Maybe later

• JS/Emscripten (both in terms of Node.js interop and use of XXL in the browser)
• LLVM IR
• GUI

Probably not

• Unicode

Installation

Pretty rough right now. You'll need a C compiler and a minimally POSIX environment but that's about it.

Customize your build

XXL is meant to be tailored to the device you're using it on. You can remove You can customize the features that XXL includes out of the box.

We use a build script called ./c instead of a Makefile. It tries to make some guesses about how your system is configured and what options are best to use. We use a shell script to keep it simple (without having to resort to Autoconf). When in doubt, you can make your own decisions by editing the c source. It's very simple.

Around line 15 of this file you'll see a line like:

STDLIB="-DOCTA -DSTDLIBFILE -DSTDLIBGLOB -DSTDLIBMBOX -DSTDLIBNET -DSTDLIBSHAREDLIB -DSTDLIBSHELL -DSTDLIBXD "

Each of those "-D" statements enables a feature. You can remove those features if you don't want any of them.

In particular, on platforms that do not support glob.h you should remove -DSTDLIBGLOB.

If you're on a 32 bit system that doesn't provide support for 128bit integers, which we call octawords in XXL, remove -DOCTA.

If you don't have support for sockets on your platform, remove -DSTDLIBNET.

No filesystem? Remove -DSTDLIBFILE.

Without threading? Remove -DSTDLIBMBOX and -DTHREAD in DEFS a few lines above.

Not Unix-like? Remove -DSTDLIBSHELL.

No shared libraries, or don't care for dlopen? Remove -DSTDLIBSHAREDLIB.

Regenerating auto-built .h files

Some of the .h files in the source are automatically generated by some primitive .js scripts. If you don't have Node installed, or don't care to rebuild those (it's not necessary unless you change the definitions of the built in data types), just comment out "BUILDH" at the top of the ./c script.

Try something like:

git clone https://github.com/tlack/xxl.git
cd xxl
./c

The default build has a TON of debugging info turned on which it will violently spit at you while you use it. Commented out the "DEBUG=" line in ./c to make the system more silent and friendly - but perhaps less predictable when things go wrong (which they will.. often).

Turning off debugging also allows XXL to run much more quickly.

Size

XXL is about 3,000 lines of hand-written C, plus 2,000 lines of auto-generated .h files. Stripped executable is about 400kb.

I dislike large systems and aim to keep XXL small, but I also want programmers to be able to easily get at functionality they need, both through a decent set of built-ins, and through something akin to npm (still pondering this).

I believe XXL could be reduced to 1,000 lines or less of JavaScript or another language that offers a more flexible type system than C's. I also wrote different versions of similar code a lot for speed; implementing everything in terms of each() (and other forms of iteration) would probably require much less code.

Inspiration

K4/Q by Kx Systems™, the quirky Klong by Nils Holm, Erlang (process model, introspection, parse tree/transforms), Kerf's approachablity, Io (self-similarity of objects and asceticism) and C (simplicity, performance, rectangularity of data).

Imminent Rename

(I was trying to make this an eminent domain joke.)

I'm considering renaming XXL to tx, so if you see some mixing of names here and there, please be patient with me as I consider this change. Input appreciated!

Contact, Community, Chat

Visit with the XXL crew and many other smart folks on #kq and #xxl on Freenode IRC.

Credits

Wetly birthed by @tlack [email protected] at Building.co in sunny Miami

Many thanks to co-conspirators:

Eblin Lopez @ classic.com, Mike Martinez @ classic.com, Khalife Nizar @ Ironhack for keeping me grounded and much input. :)

@joebo for help with Android.

Disclaimer

No warranty. Trademarks right of their respective owners.

This project is not related in any way to the interesting XL project by Dinechin et al.

License

BSD-L (3 clause)