Make Your Own Language 5: Runtime Functions

This is the fifth episode of a series where you build your first programming language, using these videos as a guide. We’ve setup the syntax for a small programming language. You can clone this project and start getting to work. The project repository is https://github.com/airportyh/smallang. In this episode, we write some runtime functions to allow users of the language to have a baseline of capability.

Transcript

The following transcript was automatically generated by an algorithm.

00:00 : hi this is toby welcome back to the
00:02 : series where
00:03 : we make a small programming language
00:06 : from scratch uh using the nearly js tool
00:10 : as well as the mood.js lecture tool
00:14 : the language is called smalling this
00:17 : time what we're going to do is
00:19 : to make some runtime functions that
00:22 : will support this language such as print
00:27 : and add and multiply
00:30 : i meant to say multiply here but i typed
00:33 : multiple for some reason
00:34 : subtract as uh so the basic things that
00:37 : the
00:38 : typical programming language can do
00:40 : we're going to add runtime functions
00:42 : to do those so last time
00:46 : we have successfully created a generator
00:49 : a code generator
00:50 : taking this parsing it generating the
00:53 : ast
00:54 : and then using the generator to convert
00:56 : that into a javascript that looks like
00:58 : this
00:59 : so that we can make this program
01:00 : actually run and
01:02 : produce the results we need these add
01:04 : and multiply and subtract functions
01:07 : added to the runtime environment of this
01:10 : generated javascript if you can imagine
01:13 : the only things that are needed to make
01:15 : this program work
01:17 : are these functions and we can simply
01:20 : define them
01:22 : like so right but this is a generated
01:24 : file so we don't want to just
01:26 : hand edit this file so what we're going
01:28 : to do is add
01:30 : some extra runtime functions that will
01:33 : get appended
01:34 : to the outputted program here
01:37 : that way this program can actually run
01:39 : before
01:40 : actually doing that one thing i want to
01:42 : do is make a convenience
01:44 : script to automate the work of first
01:48 : having to call the parse
01:49 : script and then having to call the
01:51 : generate script and then
01:52 : having to call node.js so to do that i'm
01:56 : going to make a
01:56 : node.js file and call it runjs i have
02:00 : too many files open so let me just close
02:02 : them all
02:02 : so again i'll make a sync main function
02:08 : um and we're gonna read in a
02:11 : file which is a dot small file okay can
02:14 : actually
02:15 : steal it from one of the other programs
02:18 : to make this go a little faster
02:20 : so i'm gonna read the file name from the
02:22 : index
02:23 : 2 of the argument i will say
02:26 : please provide a dot small file and once
02:28 : we get that small file
02:31 : this is going to go through several
02:34 : steps
02:34 : as we talked about in the past we start
02:37 : with a dot small
02:38 : file we're gonna send it through
02:41 : parse.js
02:44 : which is gonna spit out an ast file
02:47 : we're gonna send it
02:48 : through generate.js
02:52 : which is going to spit out a dot js file
02:54 : and then we're going to send that
02:56 : through
02:56 : node.js that's going to send us the
02:58 : result and we
02:59 : want to print the results here
03:03 : so that's what we're doing so i'm gonna
03:04 : pre-calculate
03:06 : the file name of the ast file and the
03:08 : file name of the js file
03:10 : here so say asp file name
03:14 : is gonna be file name that replace
03:19 : that small with dot ast
03:24 : and the js file name
03:27 : is file name that replace
03:30 : that small with dot js
03:34 : okay now we're gonna use the uh exact
03:38 : function from the node.js library so
03:40 : we're gonna use this
03:41 : child process dot exec function
03:45 : however we'll use the promisified
03:47 : version
03:48 : of it they have given us an easy way to
03:51 : get a promisified version of the exact
03:53 : function
03:54 : so i'm going to just steal those two
03:56 : lines of code
03:58 : in order to get it so okay so now we
04:00 : have an exact function and with the
04:02 : exact function
04:03 : we can call any command line
04:06 : commands from a node.js program and it's
04:10 : a a sync await style function now i
04:12 : cannot wait on it
04:14 : so i'm going to say node
04:17 : parse the file name
04:20 : is the first step and then the second
04:24 : step would be
04:25 : node generate
04:28 : given the ast file name and then the
04:31 : final step should be
04:34 : node and then just the javascript file
04:37 : name
04:37 : so this should run all three commands
04:39 : one after another
04:41 : i'll run it on the example one
04:44 : file well we did get this error
04:48 : which is the add function is not defined
04:51 : which is good
04:52 : um i want a little bit more uh we're
04:55 : sort of not seeing the output of each of
04:58 : these commands
04:59 : so what i'm gonna do is uh receive the
05:02 : output
05:04 : from each of these commands so that i
05:06 : don't have to rewrite this code over and
05:08 : over again i'm going to actually make
05:10 : my own exact function which takes a
05:14 : command
05:16 : and it'll do this bit here
05:20 : and i believe the output actually has a
05:23 : standard
05:23 : out and a standard in but i'll
05:27 : print it out contour dialogue it to
05:29 : confirm that
05:30 : um so and this is just gonna take in
05:34 : this
05:34 : command that's passed in so now i'm
05:37 : going to switch
05:38 : all of these to my exec
05:42 : and it will sort of print out the output
05:44 : object which
05:45 : yeah it has a standard out and a
05:47 : standard error
05:49 : so i'm going to say okay well if it has
05:52 : a output that standard out
05:55 : let's print that guy out and
05:58 : if it has an output.standard error
06:02 : let's also print that out maybe with an
06:06 : error okay so
06:09 : that did it um oh it printed out
06:13 : an extra new line that's because the
06:15 : output already has a new line in it
06:17 : and in node.js the way you can avoid
06:19 : having an ending new line
06:21 : is by using process dot standard
06:24 : out that right like so so i'm gonna
06:27 : do that for both of these we might use
06:30 : color to color their output later
06:34 : okay so that worked the third command
06:37 : evidently
06:38 : errored out and printed this error which
06:40 : is
06:41 : kind of okay because i do get to see
06:43 : this very very blatant
06:45 : error so i'm gonna leave that b i think
06:47 : we're okay with this
06:48 : run script now let's try to give the
06:51 : program some runtime functions to use
06:53 : let's start small and let's try to get
06:56 : this program to work
06:57 : if i do note run.js and
07:00 : example two that small
07:04 : we see unhandled ast note type
07:07 : identifier
07:08 : and that was coming from the generate
07:10 : step so
07:11 : there's something actually we need to
07:13 : fix before we can even
07:15 : start this process let's fix this
07:17 : problem so generate.js
07:18 : line 44. uh we forget to handle
07:22 : identifiers identifiers are just
07:24 : variable references
07:25 : like this one right we're referring to
07:27 : the name to fix this
07:28 : is simply that we need to add a if
07:31 : statement
07:32 : to to handle that particular type of ast
07:35 : node
07:36 : and i think we can handle the exact same
07:38 : way we did
07:39 : for string and number because if you
07:41 : look at the ast of this program
07:44 : an identifier also has a value
07:47 : which is the name of the variable let's
07:49 : try this again
07:51 : um no oh i forgot to rename that to
07:56 : identifier
07:56 : brain fart
08:01 : okay now we got through that and now the
08:03 : problem is the function
08:05 : print is not defined and that was the
08:07 : problem we were setting out to
08:09 : solve in the first place so let's give
08:11 : this program a
08:12 : function called print the way i'm gonna
08:14 : do it is actually
08:15 : externalize it into a separate file and
08:18 : call it runtime.js
08:20 : in this runtime js i'm gonna put all of
08:24 : the functions
08:24 : that i want available to this program at
08:27 : runtime and i'll write print
08:30 : which is just a alias more or less for
08:32 : console.log
08:33 : i'll take all of the arguments
08:36 : as with a spread operator that means you
08:39 : can pass in any number of arguments
08:42 : and then i'll call console.log while
08:45 : spreading those
08:46 : arguments back onto the console.log so
08:49 : if you had this function then that
08:52 : program
08:52 : should work a quick way of testing this
08:56 : is you can just paste this in here in
08:58 : the generated code
09:00 : and try running it that's kind of a
09:02 : cheat
09:03 : and it does show that this works if this
09:06 : function
09:06 : existed right so now to make the whole
09:09 : thing work
09:09 : what we want to do is have this
09:11 : generate.js script
09:13 : read in this runtime js and append its
09:16 : contents
09:17 : to the output let's go ahead and do that
09:20 : so we
09:21 : again use fs.read file
09:25 : i'll say this is runtime.js
09:28 : and we'll read the runtime.js
09:32 : this time and the runtime.js code should
09:36 : be appended
09:37 : to the end of this js code so we'll just
09:39 : do
09:40 : plus runtime js
09:44 : with a new line just before it how about
09:47 : that
09:47 : so now if we're lucky then everything
09:50 : just works
09:51 : yeah everything just works great now
09:54 : let's go back to the first
09:55 : code example that needed an add function
09:58 : a multiply function and a subtract
10:00 : function
10:00 : in order for that to work i also might
10:03 : as well print
10:04 : out the sum as sum
10:07 : hope we don't have commas in this
10:09 : language so
10:10 : we already have the print function we
10:12 : just need to add these three
10:14 : more functions to the runtime
10:20 : might as well throw in a divide
10:23 : okay i think we have what it takes to
10:26 : run this file at this point so let's try
10:28 : it
10:29 : yeah the sum is three awesome is it
10:32 : supposed to be three is that correct
10:33 : four minus three is one one multiplied
10:36 : two is two
10:37 : one plus two is three yes it's supposed
10:40 : to be three
10:40 : great uh previously i have uh
10:43 : added this example three program and it
10:47 : requires a few more
10:48 : math functions you know what let's do a
10:50 : bonus and
10:52 : add all the functions that it requires
10:54 : this program to work
10:55 : okay let's have the square root function
10:57 : and the pow
10:59 : function and i think that's actually all
11:01 : that we need
11:03 : in javascript there's math dot square
11:05 : root
11:07 : so that's easy and in javascript there's
11:10 : also pow
11:12 : see if that works yeah there's the
11:15 : distance
11:16 : uh yeah so so that's adding some runtime
11:19 : functions
11:20 : i'm gonna stop this episode here next
11:22 : time i think
11:23 : it's the time to add the lambda function
11:26 : to this language
11:28 : that's kind of the big boss
11:31 : in terms of difficulty so uh i'm excited
11:34 : about it
11:34 : i hope you are too so see you next time