What Does it Mean to Make a Programming Language?

In this drive by code session WaiKit and I start a series on the topic of making programming languages. I will give an overview on what it means to make a programming language and explain what is it that you’d be making if you want to make a programming language.

Transcript

The following transcript was automatically generated by an algorithm.

00:00 : hello everybody welcome to another
00:01 : drive-by code session so my friend white
00:05 : kid and I we have been talking and we
00:07 : decided that we're going to start a new
00:10 : series on how to create programming
00:14 : languages this is I think going to be
00:17 : quite a lengthy series and I hope that
00:21 : you come along for the ride as usual
00:24 : like it is going to come up with all the
00:27 : code examples and I am going to replay
00:30 : his code sessions and then explain what
00:32 : he did and for the first episode in this
00:35 : series I thought that I would give an
00:39 : overview of what it's like or what it
00:42 : really means to be creating a
00:45 : programming language so when you're
00:47 : programming a lot sorry whenever you
00:49 : were creating a programming language
00:51 : what you need to do is write a program
00:55 : which is no different from what you're
00:58 : normally doing at the job as a
01:01 : programmer now this program is going to
01:04 : take in as input the code that is
01:09 : written in your programming language
01:12 : this might be a programming language
01:13 : that you are inventing but it could also
01:16 : be a pre-existing language if you
01:19 : decided that you want perhaps to make
01:21 : improvement to this language or you
01:23 : gonna come up with a better version of
01:26 : this programming language now your
01:29 : program is gonna take this code as its
01:31 : input and as its output is going to
01:36 : produce what it's going to produce
01:38 : machine code it's gonna miss produce
01:41 : machine code which is a set of
01:43 : instructions to be carried out by your
01:47 : CPU your central processing unit this is
01:51 : a unit in your computer let me see hmm
01:55 : there this so this is what a CPU looks
01:59 : like and you're producing machine code
02:03 : which is code that this CPU this trip in
02:09 : your computer will carry out so a CPU
02:13 : is responsible for all the smarts in
02:16 : your computer so pretty much anything
02:18 : that you can think of that a computer
02:20 : can do at some point in time it's going
02:23 : through this chip to do it so the CPU is
02:27 : the work a horse of your computer and
02:29 : then you're going to give it a program
02:32 : in the language that it understands so
02:36 : and I'll show you in just a bit what
02:38 : that machine code looks like
02:40 : and this architecture is what a lot of
02:44 : programming languages use and if you if
02:50 : you followed this architecture then the
02:53 : program that you're writing here is
02:55 : called a compiler and programming
02:58 : languages that use this architecture
03:01 : they are called compiled languages
03:04 : compare programming languages and some
03:07 : examples of these are C C++ newer
03:13 : languages that are this way or go rest
03:18 : and Haskell now this is not the only
03:22 : kind of architecture the programming
03:25 : languages can have so but but before I
03:29 : go on to the other ones I want to give
03:32 : you an example of what this machine code
03:34 : here what that looks like we're gonna
03:37 : use a C program because that as I just
03:39 : mentioned C is one of those languages in
03:42 : this family of compiled languages so
03:45 : this is a C program and Y kit chose the
03:50 : Fibonacci series
03:53 : one of the most cliched examples in
03:57 : programming so this is the input to the
04:02 : compiler program right this is a fitzy
04:07 : it's a program written in the C
04:09 : programming language and the compiler
04:13 : program that is going to take this code
04:15 : and translate it into machine code is
04:17 : called GCC and it's available on most
04:22 : UNIX or unix-like systems so if you want
04:26 : to come
04:26 : this program into machine code you say
04:29 : GCC the name of this program and then
04:33 : you tell it what is the output file the
04:38 : name of the output file you want it to
04:39 : be okay that fit and then it creates
04:43 : this fit file which is a binary file so
04:48 : my editor doesn't support binary files
04:51 : but I I'm gonna use one that can
04:54 : it's called hex fiend so if I use hex
04:59 : fiend to look at the contents of this
05:01 : binary file then I see this all these
05:04 : are a series of binary numbers and this
05:09 : is the textual representation of the
05:12 : data some of it is readable and some of
05:15 : it isn't
05:16 : this is the initialization section of
05:19 : the program which has some strings in it
05:21 : so you can actually make out some of it
05:23 : a lot of zeros will follow and then
05:26 : somewhere down in the middle of this
05:29 : file there's some interesting codes here
05:33 : now unless you are an expert in machine
05:37 : code for a particular for the particular
05:41 : processor that this these instructions
05:44 : are for you won't be able to really
05:47 : understand what's going on here however
05:49 : you can tell GCC to output a slightly
05:53 : more human readable format that will
05:56 : give you a idea of what's going on with
06:00 : a - s option here so I'm gonna ask GCC
06:04 : to compile it but this time output also
06:08 : dot s file the dot s file is what is
06:12 : called assembly language which is a
06:15 : low-level programming language for the
06:19 : purpose of basically writing the ins
06:23 : machine code instructions directly to a
06:26 : particular brand of CPU or a particular
06:28 : class of CPU in a slightly more human
06:32 : readable way so I'll show you some of
06:35 : these so for example this
06:40 : el instruction is saying can you move
06:43 : values zero to this address location in
06:48 : the memory and we have a few lists move
06:52 : to zero to this address
06:54 : move the zero to this address and this
06:57 : what this address is is that our BP is a
07:00 : register that has a number that
07:03 : represents some memory location this
07:05 : minus a is an offset from that location
07:08 : to move it to to give you a particular
07:12 : slot so this is so this offset eight is
07:17 : one memory space of set twelve is
07:19 : another memory space and offset sixteen
07:21 : is yet another one so these three lines
07:23 : actually cross bond to these three lines
07:27 : in the C code which are making variables
07:32 : and then here that I will show you just
07:35 : a couple more instructions this is
07:37 : compare and jump if greater than these
07:40 : two lines are there to make the wild
07:44 : loop work so this is basically saying
07:46 : compare the number in this address
07:51 : location and compare it to the value in
07:54 : this register which one of them is one
07:58 : one of them is the other and then the
08:00 : next line saying if one is greater than
08:02 : the other we're gonna jump jump from
08:05 : here to here but otherwise we will move
08:08 : on to the next instruction so you can
08:11 : see that there is a programming language
08:14 : that your CPU understands and it's very
08:19 : low level and it's harder to follow than
08:22 : normal program languages but it is there
08:25 : and it works it actually works really
08:27 : well so if you can manage to generate
08:31 : these sequence sequences of instructions
08:35 : in this format for the CPU that from
08:39 : sort of a programming language that you
08:42 : design and invent it then you can have a
08:45 : working programming language okay now
08:47 : what's another type of programming
08:49 : language okay so another programming
08:51 : language or
08:52 : sure looks like this
08:55 : so you're still making a program but
08:58 : this time the program you're making and
09:01 : in that program this one
09:03 : you're still making program and your
09:05 : program still is going to take some code
09:08 : as its input but this time your program
09:11 : is going to execute and directly return
09:15 : the results of executing the program so
09:19 : this program is actually executing the
09:23 : program and not just producing machine
09:25 : code to be run in the CPU if you adopt
09:29 : this architecture then the program
09:31 : you're writing is called the interpreter
09:33 : and programmer and sorry programming
09:36 : languages using this architecture
09:38 : they're called interpreted languages
09:41 : some examples of those are Python Ruby
09:48 : and JavaScript one thing one advantage
09:55 : of this this architecture is that you
09:59 : don't need a compilation step which
10:01 : means they can start up faster because
10:05 : sometimes the compilation step can take
10:07 : a while to finish but the disadvantage
10:10 : is that the running time of the program
10:13 : is not quite as speedy as compiled
10:16 : languages because machine code ran
10:19 : directly on the cpu is really fast so to
10:23 : give you an example of that Y can also
10:25 : wrote this Fibonacci program in
10:28 : JavaScript and we can execute this using
10:32 : nodejs and there it is it ran the
10:38 : program and it produced the output
10:42 : directly without going through an extra
10:44 : compilation step another type of
10:47 : programming language is called
10:50 : transparent languages that looks like
10:52 : this
10:54 : these are called transpiled programming
10:58 : languages and examples of them are
11:00 : typescript
11:02 : and CoffeeScript I'm gonna credit
11:05 : CoffeeScript with popularizing the
11:08 : notion of transpiling languages to
11:11 : JavaScript but let me talk about what
11:13 : that means to be a transpiled compiler
11:15 : language when when you're using these
11:18 : this architecture the program you're
11:20 : writing is called a transpiler and it's
11:25 : gonna take in the code in the source
11:28 : language and generate code in the target
11:32 : language but this code is still code is
11:35 : not direct machine code so this code
11:38 : might be JavaScript is one popular
11:41 : target programming language C is another
11:46 : popular one because there's a lot of
11:48 : existing infrastructure for compiling C
11:51 : once you have code in this intermediate
11:55 : programming language which again is
11:58 : still not machine code then you use
12:01 : another program to either convert that
12:04 : this code into machine code or the other
12:09 : program could be an interpreter which in
12:11 : the case of JavaScript that's the case
12:13 : that will execute that program directly
12:16 : and the nice thing about this that makes
12:21 : this easier to do then perhaps the other
12:25 : architectures is that this outer program
12:28 : you don't have to write it because
12:31 : you're relying on existing
12:34 : infrastructure to to do the next step so
12:38 : you don't have to worry about like with
12:41 : JavaScript is a browser will execute
12:43 : JavaScript directly and with C is
12:45 : there's already well established to
12:48 : change to compile C to machine code so
12:50 : you don't have to do that step all you
12:53 : have to do is translate the code in your
12:55 : programming language of choice and
12:57 : convert it to this second programming
13:01 : language and as I said an example of
13:05 : that is typescript so I'll show you
13:07 : typescript doing that so this is the
13:11 : same program written typescript it looks
13:14 : mostly like
13:15 : because it's meant to do that and if you
13:18 : go to the typescript playground you can
13:21 : put in JavaScript code and then it'll
13:23 : immediately produce the equivalent
13:25 : JavaScript code which still looks mostly
13:28 : the same as the left-hand side here and
13:30 : then this javascript code will simply
13:33 : get executed in the web browser which is
13:37 : what makes everything work and you
13:40 : didn't have to implement the web browser
13:41 : yourself because there are perfectly
13:43 : good web browsers out there available
13:46 : for free
13:48 : there's one more architecture which I
13:51 : want to cover which is slightly more
13:53 : complicated it looks like this and this
13:55 : is called a bytecode interpreted
13:58 : programming language and examples of
14:00 : these are Java C sharp and in fact Java
14:04 : Script and only over the past 10 years
14:07 : or so has javascript moved over to this
14:11 : family of languages before that it was
14:14 : simply interpreted so how bytecode
14:17 : interpreted programming languages work
14:19 : is we've introduced this notion of a VM
14:25 : bytecode and this biko is something that
14:31 : was newly invented and it is it's sort
14:35 : of like machine code but not exactly so
14:41 : this is like machine code but as it's
14:45 : not platform specific it's still very
14:48 : low-level but it's not quite to the low
14:51 : level of a real machine code so your
14:55 : program your compiler actually your
14:59 : compiler is going to take your code and
15:02 : generate vm by code instead of actual
15:06 : machine code and then this VM bytecode
15:08 : cannot be executed directly by your CPU
15:11 : it needs a bytecode interpreter in order
15:15 : to execute it so and this bytecode
15:19 : interpreter as the name suggests is an
15:22 : interpreter and you still have to read
15:24 : this guy yourself and and so
15:28 : and because it's an interpreter its job
15:32 : is to help put the results of the
15:34 : program so so in order to run the actual
15:44 : program you first have to compile it
15:46 : into bytecode and then run a bytecode
15:48 : interpreter which will execute the code
15:50 : and yields the results now the internals
15:53 : about how the bytecode interpreter works
15:55 : is as follows the bytecode interpreter
15:59 : actually has to bridge the gap between
16:01 : what the bytecode looks like and what
16:03 : the machine code looks like so inside of
16:06 : the bytecode interpreter and this is
16:10 : where the term JIT which stands for
16:14 : just-in-time compilation it will
16:17 : actually use a different color here it
16:19 : actually compiled this machine code it
16:22 : actually compiled this bytecode here
16:28 : into machine code and this guy is called
16:31 : the JIT compiler it'll do this on the
16:35 : fly so takes the bytecode
16:37 : I mean polar doesn't it takes the
16:40 : bytecode translates it into this machine
16:42 : code and sends it to the CPU on the fly
16:46 : on a function by function basis it
16:50 : doesn't do the entire thing it does each
16:53 : function as the function is needed and
16:56 : this is an approach that is more
17:00 : complicated it's basically a hybrid it's
17:03 : an attempt to have the best of both
17:06 : worlds of the compiler architecture
17:09 : versus the interpreter architecture so
17:13 : this last kind of of architecture I I'm
17:19 : gonna defer that perhaps until the later
17:24 : parts of the series because it's by far
17:26 : the most complicated starting the next
17:29 : episode I'm actually going to drill more
17:32 : into the contents of this box which is
17:37 : the probe
17:38 : and so the program whether it is a
17:46 : compiler or an interpreter in either
17:54 : case the program is going to need
17:56 : something that can take the code and
18:03 : make sense of it and that thing is
18:07 : called the parser and the parser is
18:13 : going to produce something what well
18:17 : that's what you're going to find out in
18:19 : the next episode so if you want to come
18:23 : along for the ride
18:24 : stay tuned I hope you enjoyed this
18:27 : episode and work it and I will see you
18:31 : next time