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Episode: 321
Title: HPR0321: Parrot
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0321/hpr0321.mp3
Transcribed: 2025-10-07 16:19:54
---
music
The Utah Open Source Foundation brings the Utah Logs home.
Feel free to listen live at stream.utos.org or catch the audio afterward at podcast.utos.org.
The bandwidth is provided by Center 7.
The following presentation, Parrot, was given on March 11, 2009 by Stephen Weeks at the
Provo Linux user group.
Visit their site at plug.org.
Wow.
Wow.
Happy.
Hello.
Let's see if this works again.
My ex-server wouldn't wake up.
What?
I'm not sure.
No.
I'm not sure if it works.
I don't know.
I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure.
Oh, I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure.
I'm not sure if it works.
Maybe we could, kittens or adults?
Or could we wake up?
And I was trying to log in again.
It was working before.
I'm here from Guru Lab's Parrot is really cool, so excited about Parrot.
Parrot is a, it's a virtual machine for dynamic languages and video settings.
And it's also a set of compiler tools on top of that, let me see, let's click here and
just say, no, don't be disabled, shut up.
Yes, this is how I teach all the time.
I shout profanities at my laptop, that's, whoa, am I, that will have to be good enough.
Now my display right here is very, very tiny, doesn't show as much as up there does, it's
interesting.
But I don't have an ATI card, I have zero ATI cards.
I'll just look up there, how the work.
Clint doesn't have to be nice.
Anyway, right, I was saying things, sorry, a bit flustered, I'm also a bit sick, so if
I fall on the ground coughing, just leave me for a minute, I'm sure I'll be fine.
So Parrot, like I was saying, Parrot is a virtual machine for dynamic languages and it's also
a set of compiler tools for building your own compiler for Parrot.
One of the main goals of Parrot is to be able to allow all these different languages to
interoperate with each other.
You write your Ruby script, we're getting there, right now, at this very moment, most of
that doesn't work because most of the languages library is, well, we're getting ready for
our release in six days, six days will be the Parrot 1.0 release, which is good.
How many people here know anything about Parrot, read about it, looked at it, okay.
So the main thing I'm going to present on here is I wrote a little scheme compiler in
Parrot and we're going to run through how to build the compiler and implement scheme.
I had this prepared in advance and I apparently deleted it, I'm not sure, it wasn't on my
laptop as of midnight last night.
So I wrote it again in about three hours today, so that's good.
These penguins here, the goal for these penguins is if you wanted a penguin, you have to
ask me a question during my presentation.
Your question is going to be if you can have a penguin, isn't it?
That's a meaningful question, too.
So any questions before I get started here?
It might be one on IRC.
It might be, I should, I could try to pay a tanking IRC.
Yeah, that's good.
Apparently he raised his hand but he doesn't ask the question so we'll wait.
That's good.
All right, so let's talk about Parrot.
All right, so the very first thing I did to try to build this compiler is around this.
There's this little tool of make language shell and go ahead and just run a Parrot slash
live slash one to bell, tools, dev, that's not right, I don't care, anyway, get it, check
it out, one.
Here we are, creates this little directory for you, it's got the very basics implemented.
It's with little test, which all this language is, is just say statement.
It's the word say, followed by some text and a semicolon.
So we can compile this, see if it works, then I'll show you a little bit about what we
have here.
All right, so if I run a Parrot on this steam.pbc, that's for Parrot bytecode, that's the
compiled bytecode repeating myself here, run it on, it's yours or say, so it apparently
works.
All right, so let's walk through the different stages of this compiler, the very first stage
is going to be the parsing, so we need a grammar here, so let's source, parser, grammar.pg
or program, these are purl six rules, kind of like regular expressions, and so it's
got comments here in pod, which is purls, markup, purls, commenting stuff, so you're going
to find a grammar, it inherits from the PCT grammar, PCT is the Parrot compiler tools.
All right, so we start off with a rule, it's kind of like a regular expression, there are
two things here, rules and tokens.
The difference is that in rules, white space is significant, any section of white space
is replaced with a call to the WS rule, and so it's white space in your rule here represents
white space in what you're trying to parse, right, which it'll work out, doesn't matter
that much, we'll see it in a minute, anyway, so we want to parse inside of angle brackets
is calling a named other rule, right, so it calls the statement rule, which if we look
down here, that's the liberal text, say, followed by an expression, find later on, followed
by a comma, another expression, any other, most of you familiar with regular expressions
to some degree, vaguely kind of shut up.
If anything I'm talking about just makes no sense to you at all, just throw something
at me, or shout angrily, or let me know somehow, or, no, not at me, it's no things at
pause, so, but care, anyway, calls the expressions, goes on like that, pretty straightforward, it's
a pretty simple syntax, I'm not going to get into it too much with this, we'll talk about
the scheme syntax, which I'm going to show you in just a minute, let's just go ahead
and move to that, whenever moving along too quickly, or, I'll just trust you guys to
harass me appropriately, anyway, the changes that I made here, right, a statement, which
this top rule that's where it comes in, it starts parsing here, so any number of statements
is a valid program, and after that it's either, the end of the string, so the dollar sign
means is the end, or it panics, or they syntax error, so just bail out, so first we start
with an open parenthesis, it's going to be a symbol, which I define all the way down
here as just the built-in little thing identifier, which is, you know, ASCII, I'm sorry, a word
character, letters, numbers, alpha numerics, that's what I was going for, some number of
those, and I'm giving it the name, CMD for a command that you're running on scheme, right,
the scheme syntax, hopefully all familiar with this, ASXpressions, so that'll be something
like, you know, print, hello, right, something like that, it's going to be your scheme, vaguely,
I don't actually delete no scheme, so this is based on little tutorials and grammar
references and such, and then some number of other terms, which I'm going to find down
here, become down a term, this leading a bar that's an OR, usually you'd see that in
some kind of grouping, there's no grouping, so this just means either it's a value, or
it's a symbol, right, so match those value, we come up here, that's this rule, right, that's
either an integer, which is defined right here, or a quotation, right, which is defined
here using some built and stuff, that just means either an apostrophe or the double quotes,
and then everything leading up to the trailing double product, so I am skipping over kind of
a lot, if you want me to stop and go into anything that I skip over, again, let me know,
right, and then it has to be a close, now this special little curly brace star,
close curly brace, what this means is, this is a use when we're actually trying to
transform our parse tree farther down, but let's get into that in just a minute, so first
let's see if this works, right, let's see if this parses some basic stuff, all right, so
let's recompile it, oh go away, I don't want that right now, that's my take typing
breaks thing, so my hands don't hurt, let's run parrot on steam.pbc, whoops, and let's
say dash dash target equals parse, so let's see what happens, what it spits out when we
give it a little expression, right, so let's say say hello, oh, and that's worked earlier,
aha, did work earlier today, what's, what, since when, it's interesting, oh, oh this is going
to be nice, let's see if it works anyway, what does work, so there's that, but no dump, oh,
I guess it does work now, yeah, don't worry about it, I don't care, anyway, this is our parse
tree, right, and so it takes the entire, except from that regular, from those rules, and it says,
well here's the entire parse, was this text right here, say hello, well that contains one
statement, which is, this right here, say hello, that contained a CMG, you remember earlier,
I assigned that name right, see here, CMD equals, and call the symbol rule, so CMD contains an
identifier, which was, say, there's also one term here, which, well that was a repetition, right,
it's got that star, so that's inside of an array, of size one, which contained a value,
which was a quote, which was a string literal, which was, hello, is this parse tree pretty
clear for everyone, right, this is just the, well, not repeating myself again, right, so yes,
how many people have written parses? I don't know, oh, I don't know, oh you were asking them,
not me, you're clever man, I haven't implemented any sort of compiler, well, a little bit for other
stuff, I like this a lot better than some of the other options for parsers, so anyway, the next
step is to take that, I just set up a bunch of aliases right here, all that is, is steamed
as just hard equals parse, saves me on type, right, so we want to compile this down, the next
step is an abstract syntax tree, so we're going to see, can everyone read this font size
comfortably? All right, so what we want is just an abstract representation of the sort of
things we want to do, right, this is going to be very high level view of our program, it's going
to be things like run a command with these arguments, right, so the next layer down, let me show you
what that looks like, this is a past block, past tense for parrot abstract syntax tree, there's a bunch of
classes in that namespace, right, we've got blocks, we've got operations, variables, values,
right, so we're saying that this is a block, is our entire program, and that's a declaration of
the par, we'll get into that in a minute, this is an operation, the type of operation is call, so a
function call, and this has two sub nodes, right, all of these nodes, all of these past nodes have two
parts, they have named parameters, you can see in here, so it's kind of like a Python dictionary or
purl hash, and there's also positional items, so this is kind of like a, both the hash and an array
together, or a dictionary and an array together, so the two items in here are a past var, right, so a new
variable, whose name, the name of the variable is say, and its scope is package scope, kind of like
global scope, I don't look in the namespace, and the past value is hello, so call the save function,
which is in our global namespace on the text hello, is that pretty, pretty clear, any question
now what this is doing, all right, so the way we get the, the way we get there is the compiler is
actually calling, every time it gets to one of these little curly brace, star, close, curly brace,
it calls a function often in other namespace, and it passes it this entire match, and then that
other function constructs those objects, right, so in this top rule, what it does is it says, oh well,
this is my entire program, so I'm going to make a block, I'm going to shove every item in there
as a statement in that block, right, as an operation, and so we see that's exactly what it is right here,
method top, it accepts this dollar sign slash, now this file here is written in a subset of
purl six, called not quite purl, it's a very restricted purl six, and so it doesn't support a lot
of the, a lot of the fancy things, just the basic syntax, for example it doesn't have assignment,
it only has binding, just kind of like a, by reference instead of by value, so we see right here,
it's accepting this dollar slash, that's the match object, and so that that's, everything
goes in there, when we said target equals parse, and it printed that out, that's the object that
this thing gets, so what we're going to do here is we're going to create and bind this variable,
the difference between assignment and binding isn't that much that you really need to care about,
it just means it doesn't get a new copy, it's just they're all pointing to the same data structure,
going to create a new pass block, so passblock.new, this colon and the word followed by parentheses,
that's purl six is a named argument passing, so we're going to create a block with block type
declaration, and this node thing here, that's for introspection, right, where it said,
right here, where it can tell what was going on here, right, this pass over is created from,
or this, some other stuff, yeah, not actually important, that's just extra stuff, anyway,
so we're going to iterate over, right, remember the statements, we're in array, right, it's,
our statements are in array, right, because of any number of them, so we iterate over them,
for each statement, you're going to push into it, right, because this block has a list of
statements, and a list of things it's going to do, now again we have some special syntax,
right, this is not quite purl, it's used here, it's mostly just special idioms, right,
this dollar sign parentheses means that this, if you haven't worked with purl, the dollar sign
underscore, that's the current topic, right, so for each time goes through this for loop,
it's, this dollar sign underscore is set to each item in there, don't bother with the name,
because we're not doing much special with it, so this dollar sign parentheses means get the syntax
tree representation of each of these objects, right, so, so go ahead and compile the syntax tree
for each one of those statements, and then give it back to me, and push it inside of this block,
right, so if I had multiple of those, right, I can go ahead and do that,
you know, say one, say two, we have two past ops, right, two operations in term,
pretty straightforward, and these are children at the block, so we've gone through this a little bit more,
we won't go through the whole thing unless someone asks me to, there's, well we'll get to it eventually,
right, so it's going to call the rule for those statements, right, so that's method statement,
again it accepts a match object, this says I want to create a new past op, right, an operation,
right, like a function call or a method call or something like that, on, again we see this dollar sign
so get the syntax tree of this, right, of this CMD thing, which is a symbol, and so we can chase that
down, come down here and see that for symbols, right now I'm doing, say make a new past variable,
whose name is, whatever was in the ident, part of the match, and whose scope is packet, so a
globally scope variable, right, and I'll show you in a little bit where that save function is defined,
it's not just magic, we'll get to it, all right, so inside the statement,
new past op, that past type call, so call that function, and for each one of those terms,
I remember term again was any number of these, push those into the op, okay, pretty straightforward,
and then the make command means set this as the syntax tree representation for this node,
it's kind of like return, it's slightly different for some reasons we're not going to get into,
but you can think of it as just returning it back into one of these calls here, right, that's what
that is, so any questions about how this is working, how this compiles that, that parse tree
down into a syntax tree, all right, so now parrot takes that abstract syntax tree,
next step it goes to is it compiles it down into a, well, couple steps, it compiles it down
into peer essentially, which is the parrot intermediate representation, that's essentially a
parrot's version of assembly, right, so I say say hello, it says dot sub create a new subroutine
with some garbage out here that we don't care about, so what we're going to do is we're going to
look in the global namespace, fetch it into a register, my parrot is a register based virtual
machine, not a stack based virtual machine like many others, who has done any kind of assembly
stuff, all right, so look up with this string say, and then we're going to save the result of
calling this function with the value hello, and then we're going to return it, so that's all it
does, right, pretty straightforward, any questions so far about how this works, all right, no questions,
oh, I guess I'll keep my penguins to myself, all right, so let's start implementing a little bit
more, this is a little not exciting, so let's check out next step, right, some basic math operations,
nested expressions, so let's see what we changed in here, first thing we changed, we're defining
more of these, right, in this built-ins directory, the make file compiles, you know, concatenates them
all together and then includes them in the bytecode, so let's take a look at these, all right,
the one we already have was that say function, the source built-ins say dot peer, this is just dot sub say,
we want to accept one parameter, which just slurps up, right, it accepts as many parameters,
sorry, as many arguments as we pass to it, it solves them inside of an array here called args,
yeah, that's a modifier to this, right, it says, yeah, that basically says for the calling
conventions, however many arguments are passed, just shove along into an array and put them inside
of this variable here, this is written in peer, it's a parrots assembly language,
so it's not, I mean, it looks kind of a little bit like, it's very high level for an assembly
language, so we create a new, we sign a name, parrot has four different kinds of registers,
right, there has four different kinds of registers and you see what the dollar sign out in front
for reasons we don't get into, but then it's a capital letter and a number, or four different
kinds of registers, there's PMs, well there's integers, right, so a whole number, there's
num registers, which are a float, right, there's string registers which contain some amount of text,
there's PMC registers, sensor parrot magic cookie, which basically means an object, right,
some sort of high level object, it could be an array, it could be a socket, it could be, you know,
some custom user class that you've made, it could be anything else, right,
and so this is just giving a name to a PMC register called it, it create a new object of the iterator
class, pass these args, and then just loop over it, keep pulling something out, printing it,
and then looping back, print a new line, and then we're done, so you define this little built-in,
once you get most of your language up a bit higher, you can start, you know, of course,
defining your libraries in terms of, you know, actually writing them in their own code, the
parrot's purl six implementation, for example, has a decent amount that's written in purl six itself,
I think, I think their PHP implementation might be doing a little bit of that, I'm not sure,
or a few others, anyway, we also added this math.purify, I'll just define some little basics,
so we create a subroutine called plus, which will add two values, we create a subroutine called minus,
which will subtract them, star from multiply, slash for divide.
These are actually op-codes already.
Yeah, that's what I'm saying, so you have to define those in a subroutine.
Right, this is a very high-level assembly language, which is kind of fun,
and what else do we do in here?
So we add those, and change the grammar a little bit around, I made it so that a term could
also be a statement, right, which you remember statement is a full-ass expression,
and I also changed the symbol rule to instead of just be alpha numeric to be any character other
than white space and parentheses, so that I can actually call the plus function and things like that.
All right, so if I compile this, I can then run it, and we'll say say plus one two.
Okay, pretty straightforward. Also, with each of these, I've been updating the tests,
right, so I now have that this is the tap format, what is it, the test anything protocol,
choose a law in the purl world, just print out the number of tests, and then okay one, okay two,
okay three, okay four, right, so if I make tests, it runs, T slash zero zero sanity, okay,
all tests successful. How do I actually just run steam on the file, it prints everything out?
Let's work on okay so far. Yeah.
Do you have to do like pause convention, excuse me, the drag?
In steam? Yes. Parrot actually has, and this is one reason that I kind of was a little unsure
about using steam for this, but actually has an additional way that you can use its parsing engine
to do bottom up parsing instead, so you actually just define a table of operators, right?
You define, well here, here I've got my infix plus, and I've got my prefix, you know minus to
do negatives, and they're all, you know, the infix plus is higher precedents or lower precedents,
and the infix multiply, and then you just define all those rules, and then you say can be a token
here, and we'll go through and just parse out, you know, all that infix math and all of that,
so there is some really nice stuff for that. If we have time at the end, we can go into that too,
as well, if someone wants. Someone asked a question, he gets a penguin.
All right, so what comes next? I don't even remember what order I did these in.
Up until now, I think I got about here by 1am this morning, four should come next.
Yes, yes, I got through to this part by 138, so implementation of the special form if,
right, which is just, you know, if, and then you have some condition, right,
if 1 is less than 2, then do this, otherwise do that. This is what it looks like in scheme.
Pretty straightforward, so let's actually take a look at what we changed here.
All right, so I added some comparison functions, let's take a look at those.
All right, I did sub equals. If they, if these two are equal, then jump to the true label,
which is down here, and return one. Otherwise, just fall through and return zero.
Same thing for less than greater than, less than or equal, greater than or equal.
You see, I'm just using these built-in parrot ops, which are, again, it's a very high-level language,
or assembly language. And we also did, right, there we go. I'll just pull it up.
Instead of the, whoops, instead of the diff, and what we have here is I changed the statement rule
to first check for one of the special forms, which have their own special parsing rules.
For example, instead of just like a function call, you don't want to evaluate both branches first
to pass the argument in. That would be bad if you evaluate both branches of the conditional.
So we check them both and only evaluate the one that's appropriate.
If it doesn't match any of those, then we call the simple rule, which is just what it was before.
So the special right down here, well, that's just the if rule. Now, one thing that you'll
see right here in a few places, this hash equals, then a word, that's when something could match
in a variety of different ways. And you want the parser engine to actually tell you which it was.
So the way that's actually implemented is down here in the statement rule,
and now except a second parameter here, which is a key. And that's which one of those
things actually matched, right? So what I do is I take, you know, just return the syntax tree for
the key named sub match of dollar slash, which is the match. So just actually return by far,
it's just the same thing that's in here. So it just tells you it matched simple instead of
special or special instead of simple, to simplify your rules there. Fun losing you that's not
too important. We'll see it again a few times. So it comes out here, tries to match if,
for if that's the literal text, if, and then one term, another term and a third term. So I'm
just naming them condition, if it's true, if it's false. And then we call this, right? If you're
just doing matching, right, if you're just trying to do, you know, the equivalent of regular
expression, you don't need to do anything special with it, you don't need this special curly thing,
right? So let me show you what, if, implements. So you have method if, that makes a new past operation,
it creates a new one. The three arguments are the condition, if it's true, and if it's false.
And then the past type, I saw earlier, right down here for a simple, so that's just a past type of
call, it's a function call. This past type is if, for doing conditionals, right? The
paracompilot will provide a lot of default implementations that make a lot of sense. We can
actually take a look at the documentation, docs, d, pdd, 26, st. It's also in some more reasonable
path, but that's the one I actually remember. So we look for past op, that can be past type of
copy, bind, or if the first, second, and third children represent the condition, the then,
and the else parts of a conditional expression. First, child's evaluated, if it's true, then the
second's evaluated, if it's false, and the third's evaluated. Pretty straightforward.
So we can actually see that, that's what the syntax tree looks like. We compile it,
we see if it works, we say, say, if, one is less than zero,
hello, hello, or goodbye. But if one is greater than zero, we say, hello, okay. Let's do a
dash dash target equals past, and we see it did actually make a past op of if, that's a child
of past type call, so call the save function on this past op. If you want to look at the
period generates, that's just target equals peer, if less than one zero, hello, or goodbye.
We see it get global that, if this jump to this value down here, and then go on and run these,
otherwise, make a goodbye, and then jump down to the end where it returns it. So that's what it
will generate for each one of these. It's pretty straightforward, completely losing you, and
because it was more typing. And I can do the same thing here.
Right. So in this case, the first get global say, then to the end down here, it calls this function,
which are retrieved up here, and it calls this function on which ever value it did here,
so I decided to set it to this or set it to that, and call the function on it.
So any questions so far about this? Pretty clear? All right. So the rest is just
implementing more of the special forms. So just adding more to our scheme compiler.
I think next is five? Whoa, I apparently can count. No, that's the same one. Oh wait, no, that was
previous. We'll skip that one for now. Okay, we define works, that's actually setting new variables.
Oh, oh way. Ah, right. And so we first make a grammar change, right? Here in our special rule,
say it could also be a define. And what that looks like is inside of the parentheses, right? Because
remember, special is called from something that says parentheses. So inside it, ask expression,
it starts with the literal text, define. And then I added some stuff here for error checking,
and I pulled it out later, so it doesn't matter much. But basically it's just define, and then
a variable you want to create, and what you want to set it to. Pretty straight forward, right?
And that in scheme is just define a as one. So let me show you what the grammar rule for that
looks like. It just says my variable, going to bind it to the syntax tree for variable, right,
for that match. And then I also set this is decal. That says, this is a declaration. I'm creating a
new variable here, right? It's not something that already exists, so don't try to fetch it,
just create a new one. And my value, that's that. So now we make a past op, the past type bind,
right? So actually do an assignment to this value, assign to the variable, the value.
Pretty straight forward. So we can try this, right? There are make, define, message.
Thank you, Clint.
Hello world. Say the message. It works. Fantastic, right?
Oh, I made some tests for if and for define, we run make test, we see they all pass.
See the if test pass prints out, define test prints out.
Pretty straightforward. If you want to actually look at the syntax tree for that,
right? You say steam dash dash target equals syntax tree, define a as one.
So you see it just calls bind a newly declared variable named a, that's in package scope,
but it got that from that symbol rule, right? Which creates a new variable nodes here.
And then it turns a new integer, right? Any questions about this? We okay with this?
Want me to look at anything more and more depth? Want to sit there quietly? Your face is staring
ominously. Okay. What's that? Oh, sure. Oh, below the assembly level.
Para compiles it down to what's called a PVC file, which is para byte code. So just compiles
it down to the actual binary representation of the op codes. And such.
So we can actually print it out like that. Well, we can actually do this,
that's that's a way.
I don't bother with it. Yeah, you can actually compile down your individual programs
down to a PVC. And so you don't need to strip your source with it or anything like that.
You can just run the PVC directly, right? I wonder to do something like that.
Well, that's just target equals peer. I'll put you defined there. And there's a little bit that
I'll need to change in here because I'm not generating it properly. Load byte code,
steam.pbc. You're on parodon it directly. That'll print it out. We'll write out to define.pbc.
So now we run parodon.byte code.
And actually dump it out and see here's the header, which tells me the word size,
all of that stuff. And down here's the actual op codes. All right.
Here's the constants table, which is for the literal text and such.
And so that is that is that is that about what you were asking about?
All right. So let's see what I implemented next. I don't even remember.
That was it. So that was now. 7th can count.
Let. Let is for doing lexically sculpt variables, right? So set these variables for just this block
and then they're gone. So it's kind of like many other languages you do with the curly braces
or something like that or indentation and Python, that kind of thing.
So let's actually show you what it's like. Again, it's pretty simple,
but I do need to do things a bit differently, right? Now that we've got lexically sculpt variables,
we need a way to actually track what's going on with them, right? See, you know, we need to maintain
a symbol table to say these variables have been defined here, but later on they're not defined.
So what we do is we're going to have this global variable of this at sign. Again,
this is purl six. The at sign means it's an array, a list. The question mark means it's a global
variable, right? So we're saying here's our package global variable called block and all capital
letters to show that it's weird. What we're going to do in here is as we go through and create new
blocks, they're nested inside each other, which is what let does, we're going to actually, you know,
make a new block object and save it inside of this array, right? We're just going to, you know,
shove it on the front, then every time we need to look at the current block, we'll just look at
the start of this array. We can just walk the whole thing there, right? Right, exactly, exactly.
And we also made a parsing change here, right? We're going to actually call this two times at the
very beginning, right, which is first we need to set up this stack, make our block for the entire
thing, and then again at the end, right? It was going to be called two times. So we see up here,
if the key equals begin, then we want to set us that are variable here to a new past block,
and we want to unshift it, it's purlish for, you know, shove it on the front, kind of like push,
but on the front instead of the end. So unshift this block on there. At the end, we want to actually
grab it off of the front. So we want to shift it off, like pop, but from the front,
then iterate over the statements and push them onto it, and then return it, right?
That's our change down here. Define, I actually had
do it lexically in the current block instead of globals now. So when we pull the variable out,
we set the scope on it to lexical. We also, right, first I grab my block out of
that block sub zero. So the very first one on the stack, right? So the very most recent,
and we call the symbol function on it, which is just a way to set some data in there, right? So we
keep this symbol table around, which I'm all in storing it here is the name of the variable,
and this is lexically sculpt, right? So later on, when we actually mentioned a symbol,
we can actually go back and walk up the stack and see, well, is it defined lexically anywhere?
If not, it must be a global variable, right? So try that instead. So we'll see that in a bit
down here. So the way we define let, the grammar for that is right here. What the grammar actually
looks like is let, the insider parentheses, we have a list of things inside parentheses. So we say
a is equal to one, and b is equal to two, and c is equal to three. Then over here, we can do,
you know, whatever you want, right? Say a, say b, right? That's what a let statement looks like.
So it's kind of like, you know, just defining a block in some of the little, little bit different.
Ah, I can't, yeah. So down here, what we do, oh, we also have the grammar for it.
I didn't show it. So we say we first have an open parentheses, and then any number,
well, at least one, the plus is like the star, but at least one instead of at least zero,
of open parentheses, a symbol, excuse me, a symbol, which we save under the name var and a term,
which we save under the name val, a closed parentheses, at which point, once we've parsed that much,
go ahead and call it, right? So we create our block first and, you know, save things inside the
symbol table. So the one we're out parsing the other statements, it has access to them. Then we
parse any number of statements, and then we're done, right? Call it again.
So the way we do this, right, we again use this, this global set of, you know, blocks at our little
symbol table. So if the key is begin, and we create a new past block, block type of media,
which means go ahead and run this right now, right? We're not defining some code, right? We're
not defining a function or something. This is just inline stuff to actually do, and we're going to
create a list of statements, which is like a block, but it doesn't make a new scope, right? So
just a list of statements to hold stuff in. And then for each one of the variables, we defined,
again, that's going to be a list, we want to save it inside, and we can actually look at the
parse tree as we're doing this. Oh, I already did make it. All right, so we say let a1 and b2,
then say a. Oh, that's bigger than I. Want it to be go get bigger. Yeah, there we go.
So we have our special form. It's let. It has two variables, which are a and b, because they both
get saved into that name. So it becomes an array. And we have two values, which are 1 and 2. And then
we have a statement here, which is this big thing. So what we do with it, right, for each variable,
give me the syntax tree representation of it. And then we want to shift off a value, right,
so pull a value off the front of the list of values. There would be a few other ways to write it,
so you know, work on the two lists in parallel, but I'm kind of lazy. So I'm not rewriting it.
Set the scope on it to lexical, say it is a new declaration, register it in the symbol table,
and then push it, right, push a new past off, which is we're going to bind this,
right, push that new off into the init variable, which I have to find up here. Then at the end,
we shove the init block onto the beginning of our block, right, so we start off in our block by
just assigning these variables. Then we unshift it off, right, we shove our block into this list
of block, right, our symbol table. Let me know if I'm going too fast or you're just throwing
something at me as a valid comment here, really. Anyway, if we're at the end, what we want to do is
make a list of statements, right, for each statement, push it in there, and then grab our block
off of the top of the symbol table, right, pull it off, shove our statements into it,
and then set it as the syntax tree for this node, right, for this part of the parse tree,
right, so let me show you what this actually looks like. It's pretty nice.
Past for the abstract syntax tree, let a equal the one, say a,
pretty straightforward, so we start off, we get a new block here,
right, of type of media, and it has a sim table attribute, right, so for this block,
we've got a new variable called a, which is lexically scoped, and then we want to bind,
right, there's our first child here, a list of statements, and an enlist of statements together
just concatenate, there's no difference between them, right, so first we want to bind,
right, into our new variable A, right, it's newly declared here, an integer, value of one,
and then we call our namesay, scope package, right, so our global save function,
on this value A, right, and the reason it was able to look up, right, this serialization is
pretty poor, it just references the earlier thing because that's how I got it, right, by looking
it up, let me show you, all the way down here somewhere, in symbol, yes, yeah, yeah, that's,
yeah, that's all it means, so down here in symbol, so every time we just have, you know,
just some plain text there and want to look something up, by default it's going to be global,
but in the name of it, it's going to be the stringification of the symbol match there,
then for every block, right, so we're going to start at the beginning and just walk through it,
if the block, we call the symbol function to look up a symbol from its symbol table,
and the scope is still packaged because we haven't found anything yet,
but if we find something we haven't found yet, then we just set the scope to whatever the scope
of that symbol is, it's going to be lexical, right, and then we return a new pass variable
with that name in that scope, is that pretty clear, we, all right, I keep asking that,
you can just stop that, anyway, I think we have one more thing, which is lambda's,
oh, let me actually show you that it works,
apparently works, right, for say one to three, we assign a is one, b is two, we say okay one,
okay two, okay, one plus two, and everything seems to work out, okay, all right,
make tests, still passes, all right, our four test files now,
eight, is that where we are, apparently, so lambda is just a closure, right, it's just,
you know, the lexical scope function, the function is sticking to variable,
so the syntax of it is just the word lambda, an open parenthesis, the list of parameters
that that function takes, closed parenthesis, and then a statement, video, okay, all right,
here's our examples here in the test, right, we define an, oh, using let, we set okay to be a lambda
on message, which is say the word okay, and then the message, and then here we call okay one,
okay, on a function on one, right, pretty straight, I'll stop saying straight forward, I'm sorry,
I know that was getting annoying, because it annoys me when I say it too much, anyway,
so the beginning, we had a new past block, it's a declaration, and then we iterate over these
variables, right, for each thing saved in the var name, that's a symbol, right, so we just bind
it to the syntax representation there, which makes a new past var, set the scope on it to parameter,
say, how we, we are declaring something, and then we also saved in the symbol table as a lexical
variable, and then we push it in there, right, and we unshift it off, unshift it off, otherwise,
right, so we're at the end, we take our statements, shove them into the block, set it as a return
value, and we're done, so let's look at what this syntax tree looks like, right, so I cough, and then
we check it out again, so we run past on, so make a lambda of a variable A, and we return
A times 2, and so we see that makes a past block, it's a declaration, has this lexical variable called A,
and it's got a, it's first statement in here, it's just a new parameter, right, called A,
and then it has one statement in it, which is call, the function star, on this value,
and this variable, all right, if we take a look at the, uh, pier generated by that,
let's, uh, say, uh, define, uh, double to be lambda on A of times A2, yeah, that works out,
oh, well, actually let me then call double, uh, say, double to, all right, so we first, um,
get this subroutine down here, 13 something, just see down here is named 13 something, as generated,
it doesn't give a meaningful name, it accepts one parameter, just parameter 23, that's going to be
a lexical variable, so we'll just use this little thing to say stored in the lexical symbol table as A,
and we look up the global function star, we then look up A again, because it might have changed in
the meantime, we call star on A and 2, return it, swap in here, we lexically save it as double,
get the save function, get the double function, call the double function on 2, call the save
function on double, and her done, so it generates some, okay, bike, or assembly here,
that's about it, again I have tests as well, uh, they run, make tests, everything checks out, okay,
any, any questions about this, anything you want to see more on, yeah,
what was the, uh, what was the, uh, what was the problem, the ration, it's really hard to build a
compiler, it takes a long time, it takes a lot of expertise, it takes a lot of training, and
well, if you're wanting people to be able to experiment with new things, they wanted to
enable people to go out and, you know, build their own, well that was the rationale for the
parrot compiler tools, specifically, um, for parrot, the original reasoning came around, was for
Perl 6, storage, raising a hand, yes, oh, the name parrot,
another, the m4, Perl, just like, for 5, yeah, then after the joke was done,
who in the world had that part,
she was around by the start,
so it's, what about it,
um, I can probably expand on that a little, okay, my specific interest is probably in how it does the
cross language, hybridish type stuff, and that's probably how the VM is best interacted with,
um, you can talk about how that's actually, like, conceptually just brought about, and now it's
actually implemented in some, over a high of 10,000. The way that works is, uh, each language actually
has its own, uh, its own namespace that it runs in, right, and so code that's running in
Perl 6 runs in the Perl 6 namespace, so when it, it sets a global variable, that's visible to
Perl 6 code, but it doesn't start stomping on other languages, right, it also just compiles
everything down to peer, as you saw here, right, there's nothing different from peer that's
generated by the Perl 6 compiler, versus peer that's generated by the Python compiler, or
generate by the law code compiler, or anything like that, yeah, well, for, for various, for various
meetings of support, we get different answers, um, there's currently a mostly complete tickle
implementation, a mostly complete Louis implementation, a fairly complete law code implementation,
um, of course just silly, oh, and, uh, coming along pretty nicely PHP implementation, and a
very nice, uh, Perl 6 implementation, not quite done, um, Python, there's a little bit of a,
Python compiler, but there hasn't really been enough interest in anyone to work on it very much,
um, there's, uh, there's a fully complete HQ9 plus compiler, which is a language which consists
of the letters HQ9 and plus, we're printing out hello world, printing out a quine, which is a
program that prints its own source code, printing out 99 bottles of the beer, beer on the wall,
and I don't remember what the last one was, but it's a joke language, um, there's a very
complete APL implementation, which is kind of fun to be able to call APL from Perl 6, entertaining,
um, APL is a really interesting language, um, I've been having to keep trouble keeping track of
all of them lately because, uh, right now they're being moved out of the parrot repository into their
own repositories, um, there's a, I wrote a kind of okay, uh, Ruby implementation, it's very slow at
parsing, um, once the program is actually compiled it runs okay, but it's very, very slow, I started on a,
small talk implementation, but the grammar's mostly complete, there's no standard library,
so it's useless, mostly, um, scheme implementation, Perl 6, and there's a huge, there's a big
wiki page on the parrot wiki that has all of the others that I'm not remembering, this is
everything that nobody's bothered to move over yet, awesome, basic, uh, be fun, implementation is
just scary, um, a few others that I know I'm forgetting, let's, I at least name all the big ones,
two, some degree, some languages of, well, the active languages have had that problem, yes, um,
but yeah, the parrot 1.0 is going to be out next Tuesday, is there a lease, and the headline for
parrot 1.0 is it's a stable API for language implementers, which means they're going to have,
start having a stable long term deprecation cycle, after this release, then the next major release,
there's still some bike shedding on what they're calling a major releases, deprecation releases,
whatever releases, but the next release that affects the deprecation cycle will be in June or July,
forget which, and then after that it's going to be on a six month cycle, right, it's going to be
every January, every June, right, so every six months, yeah. So is, uh, this 1.0 milestone, is that,
give us any hope of seeing pro-six? Parrot is separate from the pro-six development,
the pro-six compiler on parrot is currently passing, I think it's coming up on around 8,000 tests
from the, instead of spec tests, there has been some speculation that a complete set of tests will
be somewhere around 15,000, we're not there yet, we're still working on the test suite as well, so
I would not be surprised if it was released in 3rd or 4th quarter this year, the first
actual release of Rukudo was just this past month, it was alpha something named, but there was a
release and it's going to continue having a monthly release cycle just as a parrot has been
for, you foreseeable future. There's a lot of stuff that can be done if you want to help,
so it's still a lot of, so a lot of work that's pretty accessible, even if it's just on the test suite,
so pro-six is coming up right here, so that's actually pretty exciting, I can, uh,
oh, I think I already compiled that, oh, that's really cool, everything's all screwed up right now,
because, uh, parrots moving towards a lot of things are trying to rely on an installed parrot,
instead of a parrot from the build tree, and so right now, and I just changed around to that,
at around 12, 30 this morning, so there's still a few things that are fighting over which version
of parrot it's using, and yeah, that's not something you'd run into on a reasonable system,
it's not all hose, anything else you want to talk about?
Parrots targeted platforms are Windows, macOS, I know we've got both Intel and PPC, macOS,
64-bit and 32-bit Linux, they're looking to get packages in Ubuntu, packages in Fedora,
packages in Debian, they've been fighting to get packages in Debian for the past year and a half,
because everyone who keeps trying to sponsor them just disappears and doesn't respond to emails,
I know we have a few people running it on various BSDs, I don't know if they are in the officially
supported set or not, any other platforms you're curious about? There has been a lot of interest
in getting a running on mobile devices. Another interesting thing that I saw was some people were
working to get it running as a Firefox plugin, so you could then write your scripts instead of
in JavaScript in any language pair of supports. Not that I know of.
There has been some work at getting Java bytecode to run on Parrot, so you could then interoperate your
compiled Java classes with, you know, use them from Parrot, which is interesting as well,
as there's another project getting .NET bytecode running on it too.
It's fun though.
With Java that was originally Jonathan Worthington, who wrote most of it,
I know he is doing some kind of DBI stuff, but I'm not sure why.
Let's say your Python code or even really wanted to do your hash script to act as any database through
a little bit of a DBI. Who else wants a penguin?
Be careful you got a wire.
Oh, all the way back there. I'm out of penguins now.
The bytecode is a cross-platform. You compile your bytecode on one system. It will run that exact same
file on any other architecture, regardless of NDN, regardless of processor.
Right, as long as you have Parrot installed that, but it's not machine code. The closest you
can get for that is there is a tool, which will embed a Parrot interpreter into a piece of
bytecode, embed some bytecode into a Parrot interpreter to make a fake cutable instead of an
executable, which is kind of silly, but works out.
What's that? Now, performance, there are few bottlenecks in performance. Performance right now,
I actually did have some statistics. I don't remember when I made these, but at the time,
this was running on an unoptimized Parrot, and this is measuring some kind of loop or something
running on the cardinal, which was my Ruby implementation on Parrot against the C version of
Ruby. And about a ten times performance difference, but I was not able to run it on an
unoptimized Parrot, so there was no jits, no kind of optimization at all. But there are two
few big bottlenecks. One is the current Parrot architecture. There are several places where we go
back and forth from C calling conventions, and Parrot calling conventions, and back and forth
several times, which just kills performance horribly. And there are plans to fix that,
but nobody has implemented them yet. There's a plan how to do it, it's just a lot of work,
so it hasn't happened yet. Also, garbage collection, right now Parrot uses a stop-the-world
market sweep, everything, garbage collector, which is, well, slow and bad. There have been a
couple of projects to implement a generational garbage collector on Parrot. Apparently, it is
mostly done, but just needs to be merged in and touched up, and it's been that way for a few months
waiting for someone to finish it off. That was part of someone's Google Summer Code project,
partially a few of the other Parrot contributors were working on it. So
the core Parrot developers that I've talked to about this have very good hopes for Parrot's
performance in the future. It's not horrible right now. It's not, you know, thousands of times slower,
like a few things I've seen, but it's still, you know, not fast right now. Is that
bad on the order you wanted to know? For example,
let's just throw something together, i0 equals 0, greater than i0, a big number. Let's put another
zero on there. I don't want to count them. Loop, and increment i0, go to loop.
So let's run that. Oh, that was not enough zeros.
Let's make a thousand times more.
There, that was about three and a half seconds to run that many iterations. So in spinning
the CPU uselessly, at least it can do that much. That's in no means a reasonable benchmark,
not a very useful one, but it does mean something. There's also,
it does have a jit, which is not as good as it could be yet. Not quite everything can be jitted yet,
but I'm told there are plans for everything to be, so let's see about that.
Anything else?
How fast can you type?
Maybe that.
The Python interpreter or compiler right now does not very much. I can do the basics,
define a class, call a function, define a function, instantiate a class, the basic stuff like that,
but it doesn't have list comprehension, it doesn't have a lot of the fun stuff.
What about the constructs that are different between languages? How does Perry handle that?
Kind of thinking of examples of, and I really don't have a good understanding of
enough languages to actually say which one has different stuff in them. I know there are different
components in different languages. How does it deal with that in regard to like, so maybe in Perl,
there's some magical object in the structure in certain way, and it's different in Python,
where they build them. How does that, I mean, guessing it's in the interpreter itself in Perl, but
if it's fundamentally different, should they accomplish similar goals? The good example maybe is
like a reading loop that you think is differently there? The way that works is that the compiler
generates the same, it's always just generating peer. So control constructs like that, like loops,
and, you know, whatever else. There are several things like that I can see, that's the problem.
I'm thinking more like, you know, something abstract that probably got implemented in some language
that people use. I mean, there's probably examples, I'm not articulating that word, but
in general, most of that stuff is exposed through the same core parent primitives. There are a few
places that things are weird, for example, most scheme and list implementations that you look at.
Don't use an array, is there that object? They have, you know, the nested cons cells, which if
you implemented your language like that, if another language tried to work with one of your objects,
it would be weird. You couldn't do array access on it. You'd have to call the, you know,
the foreign function to do it. The parent took me to account that. He said, oh, that could be like an
array in this language and that. I can actually fill, I guess you could. The parent stance on that
is that they don't do anything like that. They do not define any kind of policy. You could define,
you know, the module in Python that would, you know, kind of wrap that foreign class, right? Like
to find your scheme module, right? So you'll import scheme, right? And then you could call scheme
functions. That's a reason of a way to deal with that. But there's nothing in pair that tries to
do that automatically. That tries to convert objects from one type to another type. Well, there's
what we don't know. For example, in Ruby, a lot of the core classes like integer and string and
such have a lot of methods on. And depending on how you implement things, if you just, you know,
if I returned a string from Perl 6 to some Ruby code, the Ruby code working on it would, you know,
if you tried to call that method, there's no method like that on this object, right? You could
just call the Perl methods because that's a Perl object, right? It's just a different class.
Right? So it doesn't translate that. Right. Exactly.
And that makes sense. That has never been implemented. So it's been pushed off until someone
implements it. It is not part of the one point or release. It is still part of the plan for the
eventually we'll do this magic ponies release number. But currently there's no STM.
The things it does have, it does have good threading, it does have a good event model.
The object model is Perl 6's object model, which is a 2% of all other object models basically.
So one interesting thing has been seen that you can define, you know, using roles in such
on other languages that don't normally support that. One tension that has existed has been,
it would be so easy to add this to my language, but the language doesn't support it. For example,
I added the gather take control structure from Perl 6. I added that to Ruby, a Ruby compiler,
because it was easy and made some things nicer to work with. But if anyone writes that in their
Ruby code, it will be not bad. But it was kind of fun actually calling Ruby functions, which would
take a variable and have that interoper with the Perl 6 gather construct and things like that.
What I've seen is one of the benefits of Perl 6 is that if other open source language is a chance to
be able to truly open source and gather the core work from another language that's abstracted to there.
So that's what Perl's tried to do all along with it now, sharing that same core.
Right now, all of the languages that I implemented, the
call code in another language construct in. If you try to use it, we'll still look for that
language to be in the language's directory of a paired installation, which it probably won't be,
because like I said, all the languages are moving out. There's some infrastructure work that's going on
on actually, where the language is going to be installed, and Perl can look them up for you, and
I'm not sure how that's been working out because I haven't been following that mailing list thread.
Right now, none of that works. After I think two or three months ago or something,
I posted a blog post about I got all of it working and the fun examples and such.