README

  ~ readme ~

           .ooo
            'OOOo
        ~ p ooOOOo tion ~
            .OOO
             oO      %% a little
               Oo    fast language.
              'O
               `
              (o)
          ___/ /          
         /`    \ 
        /v^  `  ,
       (...v/v^/
        \../::/
         \/::/ 


  ~ potion ~

  Potion is an object- and mixin-oriented (traits)
  language.

  Its exciting points are:

   * Just-in-time compilation to x86 and x86-64
     machine code function pointers. This means
     she's a speedy one. Who integrates very
     well with C extensions.

     The JIT is turned on by default and is
     considered the primary mode of operation.

   * Intermediate bytecode format and VM. Load
     and dump code. Decent speed and cross-
     architecture. Heavily based on Lua's VM.

   * A lightweight generational GC, based on
     Basile Starynkevitch's work on Qish, with
     ~4ms per GC on average with < 100MB heaps.
     <http://starynkevitch.net/Basile/qishintro.html>

   * Bootstrapped "id" object model, based on
     Ian Piumarta's soda languages. This means
     everything in the language, including
     object allocation and interpreter state
     are part of the object model.
     (See COPYING for citations.)

   * Interpreter is thread-safe and reentrant.
     I hope this will facilitate coroutines,
     parallel interpreters and sandboxing.

   * Small. Under 10kloc. Right now we're like
     6,000 or something. Install sloccount
     and run: make sloc.

   * Reified AST and bytecode structures. This
     is very important to me. By giving access
     to the parser and compiler, it allows people
     to target other platforms, write code analysis
     tools and even fully bootstrapped VMs. I'm
     not as concerned about the Potion VM being
     fully bootstrapped, especially as it is tied
     into the JIT so closely.

   * Memory-efficient classes. Stored like C
     structs. (Although the method lookup table
     can be used like a hash for storing arbitrary
     data.)

   * The JIT is also used to speed up some other
     bottlenecks. For example, instance variable
     and method lookup tables are compiled into
     machine code.

  However, some warnings:

   * Strings are immutable (like Lua) and byte
     arrays are used for I/O buffers.

   * Limited platform support for coroutines.
     This affects exceptions. I'm and feeling
     rather uninspired on the matter. Let's hear
     from you.

   * The parser is not GC safe. This affects eval.
     Do not waste too much memory inside eval.

   * No OS threads yet.


  ~ a whiff of potion ~

      5 times: "Odelay!" print.

  Or,

      add = (x, y): x + y.
      add(2, 4) string print

  Or,

      hello =
        "(x): ('hello ', x) print." eval
      hello ('world')


  ~ building and installing ~

      $ make

  Look inside the file called INSTALL for options.


  ~ how it transpired ~

  This isn't supposed to happen!

  I started playing with Lua's internals and reading
  stuff by Ian Piumarta and Nicolas Cannasse. And I,
  well... I don't know how this happened!

  Turns out making a language is a lovely old time,
  you should try it. If you keep it small, fit the
  VM and the parser and the stdlib all into 10k
  lines, then it's no sweat.

  To be fair, I'd been tinkering with the parser
  for years, though.


  ~ the potion pledge ~

  EVERYTHING IS AN OBJECT.
  However, OBJECTS AREN'T EVERYTHING.

  (And, incidentally, everything is a function.)


  ~ items to understand ~

  1. A traditional object is a tuple of data
     and methods: (D, M).
     
     D is kept in the object itself.
     M is kept in classes.

  2. In Potion, objects are just D.
  
  3. Every object has an M.

  4. But M can be altered, swapped,
     added to, removed from, whatever.

  5. Objects do not have classes.
     The M is a mixin, a collection
     of methods.

  Example: all strings have a "length"
  method. This method comes with Potion.
  It's in the String mixin.

  6. You can swap out mixins for the span
     of a single source file.

  Example: you could give all strings a
  "backwards" method. But just for the
  code inside your test.pn script.

  7. You can re-mix for the span of a
     single closure.

  To sum up:

  EVERYTHING IS AN OBJECT.
  EVEN MIXINS ARE OBJECTS.
  AND, OF COURSE, CLOSURES ARE OBJECTS.

  However, OBJECTS AREN'T EVERYTHING.
  THEY ARE USELESS WITHOUT MIXINS.


  ~ unique ideas (to be implemented) ~

  Potion does have a few unique features
  underway.

  * It is two languages in one.

  The language itself is objects and closures.

      Number add = (x): self + x.

  But it also includes a data language.

      app = [window (width=200, height=400)
        [button "OK", button "Cancel"]]
      
  The code and data languages can be interleaved
  over and over again. In a way, I'm trying to find
  a middle ground between s-expressions and stuff like
  E4X. I like that s-expressions are a very light data
  syntax, but I like that E4X clearly looks like data.

  When s-expressions appear in Lisp code, they look
  like code. I think it is nice to distinguish the two.

  * Deeply nested blocks can be closed quickly.
  I don't like significant whitespace, personally.
  But I don't like end end end end.

      say = (phrase):
        10 times (i):
          20 times (j):
            phrase print
      _say

  The closing "_ say" ends the block saved to "say" var.

  Normally, blocks are closed with a period. In this case
  we'd need three periods, which looks strange.

      say = ():
        10 times:
          20 times:
            "Odelay!" print
      ...

  If you prefer, you can give it some space. Or you can
  use a variable name introduced by the block,

      say = (phrase):
        10 times (i):
          20 times (j):
            phrase print
      _ phrase


      say = (phrase):
        10 times (i):
          20 times (j):
            phrase print
        _ i
      .

  Maybe it all looks strange. I don't know. I'm just trying
  things out, okay?

  * Elimination of line noise.

    I avoid @, #, $, %, {}.
    Stick with ., |, (), [], =, !, ?. Easier on the eyes.
    These are common punctuations in English.

  * I try to defer to English when it comes to punctuation rules.

  Period means "end". (In other langs it means "method call".)
  Comma breaks up statements.
  Space between messages gives a noun-verb feeling.

      window open (width=400, height=500)


  * Named block args.


      (1, 2, 3) map (item=x, index=i): i display, x + 1.


  * Assign is match + bind really (~ planned ~).

  Assignments are side-effects only, but here extended.  Atoms on the
  left-hand side (lhs) are trivial, but we prefer the power of LISP's
  destructuring-bind within macros, or prolog or elixirs matching. So
  = is actually a match operator which will recursively check if the
  expressions on both left and right side match, and binds all found
  lhs variables.

      (1, x) = (1, 2) => (x=2)
      (1, x) = (2, 3) => false
      1 = 2           => false

  _ is a special variable which matches everything, but is never bound,
  | seperates the head and tail from a list or lick.

  So we can check trees like this:

      (_, x, 2)   = (0, 1, 2)   and say x #=> 1
      [_, [x, 1]] = [0, [1, 2]] and say x #=> 1
      [_, x]      = [0, [1, 2]] and say x #=> [1, 2]
      [_ | x]     = [0, 1, 2]   and say x #=> [1, 2]

      fun = (a, b): [0, [a, b]].
      [_ | [x, 1]] = fun(1, 2)  and say x #=> 1

  ~ feverish and fond thankyous ~

  why is gravely indebted to Basile Starynkevitch, who fielded
  questions about his garbage collector. why favors French hackers
  to an extreme (Xavier Leroy, Nicolas Cannasse, Guy Decoux,
  Mathieu Bochard to name only a portion of those I admire) and
  is very glad to represent their influence in Potion's garbage
  collector.

  Matz, for answering why's questions about conservative GC and
  for encouraging him so much. Potion's stack scanning code and
  some of the object model come from Ruby.

  Steve Dekorte for the Io language, libgarbagecollector and
  libcoroutine -- I referred frequently to all of them in
  sorting out what he wanted.

  Of course, Mauricio Fernandez for his inspiring programming
  journal housed at http://eigenclass.org/R2/ and for works
  derived throughout the course of it -- extprot most of all.
  Many of my thoughts about language internals (object repr,
  GC, etc.) are informed by him.

  Ian Piumarta for peg/leg. We use a re-entrant custom version
  of it, but the original library is sheer minimalist parsing
  amazement.

  Final appreciations to Jonathan Wright and William Morgan
  who pitched in, back in the wee hours of Potion's history.
  Thanks.


  ~ license ~

  See COPYING for legal information. It's an MIT license,
  which lets you do anything you want with this. I'm hoping
  that makes it very nice for folks who want to embed a little
  Potion in their app!