Make a Parser with Nearley.js

In this episode we’ll add function expressions to our arithmetic syntax and Toby was force to go off script as Waikit forgot to implement the power functions. We’ll see if Toby holds it together. Again we’ll use Nearley.js as the parser generator.

Transcript

The following transcript was automatically generated by an algorithm.

00:00 : hello there welcome to another video
00:01 : about building parsers using nearly Jas
00:04 : so at this point we're gonna continue
00:07 : from last time in which we made this
00:12 : parenthesis syntax work for this
00:17 : calculator we've been working on so at
00:20 : this point our calculator is able to
00:23 : take some calculation based on that
00:29 : subtract multiply that were divided and
00:33 : give you the calculate the answer for
00:36 : you and it can this syntax can support
00:41 : parentheses now so this should first do
00:46 : this calculation this calculation and
00:48 : then the total calculation combined
00:52 : let's see if it works
00:53 : point six six six repeating so this is
00:57 : should be six four divided by 6
01:01 : that's right point six six six repeating
01:04 : is two over three so that that seems
01:06 : correct so now in this episode we're
01:08 : gonna add the ability to have built-in
01:12 : functions such as square root square
01:16 : power I don't remember if we did power
01:20 : sign and this syntax is gonna be like
01:24 : this so it's gonna be something like
01:28 : square root of four should get us two
01:39 : for example I think we're also doing
01:40 : power so we do power like this the
01:44 : answers should be 4 so this syntax
01:46 : involves a short name for the function
01:50 : so that's the function name and left
01:55 : paren and a right paren
02:01 : my writing is horrible
02:04 : and then some some some normal
02:08 : expression in them inside of as the
02:12 : argument of the function and I would
02:14 : just be whatever at up at this point
02:17 : whatever expression this calculator can
02:19 : handle and the whole thing is yet
02:22 : another expression which can again be
02:24 : compounded with some other symbols to
02:30 : create a even more complicated
02:33 : expression so let's see how we did this
02:36 : way kick wrote this code and I'm gonna
02:39 : replay what he did and I explained his
02:43 : train of thought as we go okay so so the
02:48 : way we're gonna do it is we you created
02:51 : this thing last bit so called uneri
02:54 : expression which is like it's a
02:56 : one-owner e meaning one whereas binary
03:00 : meaning two so an under a expression is
03:03 : visually thing only has one thing in it
03:06 : and we said that that was an expression
03:09 : that's surrounded by parentheses or it
03:11 : could be a number I'm gonna add one more
03:13 : thing to it now it's gonna be is gonna
03:16 : be the result of executing a function
03:18 : we'll call that the function and then
03:21 : define it so what is a function a
03:23 : function is a function name first a
03:25 : function name it's actually gonna call
03:27 : it built-in function okay function name
03:29 : and then an O right parameter or I
03:33 : should say left parameter and then an
03:36 : additive which is like some expression
03:41 : and then I write print that makes sense
03:45 : and what is a built-in function let's
03:47 : have some building we're gonna have
03:49 : square square root sine cosine absolute
03:52 : value we didn't even add power here oops
03:55 : I think he forgot to add power
04:01 : we might have to rectify that later but
04:04 : okay so how are you gonna do the
04:07 : calculation here well depending on which
04:09 : built-in function it is we're gonna have
04:10 : to do a different thing that's why we're
04:12 : gonna use a switch statement
04:14 : we're gonna pick so there's a FN is name
04:17 : of the function which was picked out of
04:20 : this array of matches here and if you
04:22 : remember this array of mattress is like
04:25 : this and I'll write the indices for you
04:30 : here the first one is zero second one is
04:32 : one etc Oh again my handwriting is
04:37 : horrible
04:38 : so data at zero that's that the built-in
04:41 : function and they'll give you the
04:42 : function name because that came from
04:44 : over here oh we need some IDs here to
04:49 : unpack this one I think you'll have to
04:52 : do that pretty soon and then the value
04:55 : is gonna come from index 3 this one so
05:00 : the additive is gonna come in here and
05:02 : that will get us the value because our
05:04 : editors symbol already will calculate
05:07 : the number for us at this point okay and
05:11 : then so depending on what the function
05:14 : name is if it's a square and we're just
05:17 : gonna multiply the value by itself if
05:20 : it's a square root we're gonna use
05:21 : JavaScript's math square root function
05:27 : okay he's testing the square root
05:30 : function out in genius make sure that
05:34 : exists and in JavaScript there's also a
05:37 : sine function cosine further than the
05:38 : absolute function and again he forgot
05:40 : about the power okay so we're gonna run
05:43 : the parser again and then let's see if
05:47 : it handles the square root function now
05:50 : no why is that probably because he
05:54 : forgot these IDs okay so putting them
05:58 : back in now makes it work and if you
06:02 : don't know what these IDs stand for I'll
06:06 : go back to our I believe the second
06:11 : second video in this series about using
06:16 : nearly je s and will have an explanation
06:18 : about why this ID transformer function
06:22 : is needed and yeah at this point we're
06:25 : able to we're able to call these
06:29 : functions that seems pretty cool let's
06:33 : do absolute value so like if I do - -
06:37 : for ABS here so absolute value of 2
06:44 : minus 4 is 2 2 times the square root of
06:48 : 10 is 20 the square root of 16 2 times
06:54 : the square root of 16 is 4 4 times 2
06:57 : okay so we've got these functions
07:00 : working now and they all right
07:02 : let's go off script here and make powers
07:06 : work so in order for powers to work here
07:09 : we actually need to be able to support
07:12 : multiple arguments so we need a thing
07:15 : called argument list and then use the
07:17 : recursive trick to have multiple
07:20 : arguments so first of all let's call
07:23 : this guy argument list and then define
07:29 : what that is okay so an argument list
07:34 : can either be just one argument or it
07:37 : can just be an argument in there
07:39 : followed by yet another argument list
07:41 : which allows it to recurse what's an
07:44 : argument we'll start with additive right
07:46 : I'll start with our editor series
07:48 : additive some optional whitespace a
07:52 : comma some more optional white space and
07:55 : then another argument list or it could
07:59 : simply be one additive and let that be
08:02 : yet yeah let's go with that
08:06 : there's a possibility of allowing empty
08:09 : argument list but I'm actually not Debbi
08:13 : for something like generating a random
08:14 : number or something nothing gonna not
08:17 : allow that for now and if you do want to
08:22 : allow it I'll give that to you the
08:25 : viewer as a homework assignment okay so
08:29 : Oh actually this is not gonna work
08:32 : because we want to represent an argument
08:34 : list as an array so we're gonna take
08:38 : this edit path here take the data from
08:44 : it and return an array that takes the
08:49 : zero element or the first element of
08:51 : this match but this one where I know the
08:56 : argument list is gonna get returned me
08:58 : an array probably from this one I'm
09:01 : gonna also return an array so data is
09:04 : gonna return an array which has data
09:07 : zero in it so zero is that one and then
09:11 : what's this one zero one two three four
09:16 : this is for I'm no this data at four is
09:20 : gonna be give me an array because here
09:24 : I'm returning array and the other one
09:26 : also returns me array so I'm gonna
09:27 : spread it into this array so now this
09:31 : argument list it's going to be could
09:39 : have multiple things in it so data at
09:43 : three is gonna be the arguments uncle
09:47 : arcs could be more than one value but in
09:53 : these cases they're not gonna be more
09:57 : than one value so I'm gonna say first
10:00 : part is X 0 and second part is arts one
10:10 : and then
10:13 : change these value references to first
10:17 : art and then for power I'll do math at
10:25 : POW has in first art and then second
10:29 : argh okay so now that's done they can
10:33 : regenerate the parser can be a run gen
10:39 : parser and then let's try power POW to
10:49 : to to third oh that does not work
10:58 : oh I know why I forgot to know I don't
11:04 : know why let's read the error message
11:06 : unexpected P instead of instead I was
11:10 : expecting to see one of the following oh
11:13 : I didn't add power to the list of
11:16 : built-in functions that is why okay
11:23 : fixing that I'm gonna send a parse for
11:27 : one more time and now it works we can do
11:32 : powers now two to the fourth is 16 2 to
11:38 : the fifth so what is 2 to the 12th 4096
11:46 : awesome now you know your binary numbers
11:49 : um and that's I think that's a good
11:52 : place to stop for this episode and I
11:55 : hope to see you next time for some more
11:57 : parser in some parser information some
12:03 : information about parsers next episode
12:07 : we'll probably get in more into AST
12:10 : abstract syntax trees so if you're
12:13 : interested in that I will see you next

Make a Parser with Nearley.js - Part 7

Transcript