114: The Business Case for Experimentation with Elm with Dillon Kearns

Guest:

Dillon Kearns: @dillontkearns | GitHub | Incremental Elm

In this episode, Dillon Kearns joins the show to talk about techniques for experimentation with Elm, making those experiments safe, the concept of mob programming, why you would want to experiment with Elm in the first place, and how you too can begin to experiment with Elm.

Resources:

• Grant Maki's talk on experimenting in your team
• "Types Without Borders" by Dillon Kearns @ Elm Conf 2018
• Dillon's Elm GraphQL library
• How Elm Code Tends Towards Simplicity by Dillon Kearns
• The CSS as ByteCode Talk by Richard Feldman

This show was produced by Mandy Moore, aka @therubyrep of DevReps, LLC.

Transcript:

CHARLES: Hello, everybody and welcome to The Frontside Podcast, Episode 114. My name is Charles Lowell. I'm a developer here at the Frontside. With me today as co-host on the show is David. Hello, David.

DAVID: Hey, guys.

CHARLES: David is also a developer here at Frontside and we are going to be talking about something that we've been talking, I guess a lot about recently and we're talking about Elm. I think we first started talking about this several years ago and then it kind of simmer down a little bit but recently, it's been top of tongue. With us to talk about Elm today is Dillon Kearns. Welcome Dillon.

DILLON: Thank you so much for having me.

CHARLES: I understand that you are a full time Elm consultant. You have a background as a Lean and Agile coach but have recently transitioned to doing Elm consulting full time. Now, what exactly does that mean in 2018 to be an Elm consultant.

DILLON: Actually a lot of my motivation for getting into Elm consulting in the first place is I kind of realize that Elm to me is just an extension of the things that I was passionate about with Agile and software craftsmanship. I'm trying to help teams have a better experience with their code, make it more maintainable, make it easier to change, make it easier to drive things based on customer feedback and I really believe that Elm helps people do that. I used a lot of the background and experiences that I've had with Agile and Lean coaching and a lot of those same skills, in order to help organizations adopt Elm.

One thing I've seen a lot of teams struggling with is trying out a lot of different frameworks. I've encountered teams that have spent months, very painfully trying out different frontend frameworks and having trouble coming to consensus about that. One of the things that I think really helps address that is having an experimental and iterative approach, that you can really use the scientific method to focus on learning, rather than getting it right the first time. I think that there's really a need to help teams through that process of introducing a new frontend framework like Elm, so that that's why I've gone into full time Elm consulting.

CHARLES: That's an interesting process. It sounds like you really need to be constantly sending out spikes, doing research on whether it's Elm or some other technology to help you kind of bridge the chasm to the next generation. How do you actually do that as an organization? My guess, this kind of a question independent of Elm but maybe we can talk about how you see that play out in the context of Elm.

DILLON: Right and actually, for any listeners interested in that question, I would really highly recommend Grant Maki's ElmConf talk from this year. He spoke about exactly that topic and it was at ElmConf that it's relevant whether your team is considering Elm or looking at other frameworks. I think that the key is you need to get good at experimenting in a way that's low risk and in a way that you can be constantly learning and seeing how these different technologies fit in your codebase and fit for your team.

There's a quote that I really like from Woody Zuill. Have you guys heard of mob programming before?

CHARLES: I heard of mob programming from a paper by Richard Garfield a long, long time ago, almost 20... I don't know if it's the same concept.

DILLON: Yes. It gained a lot of momentum these days. Mob programming is essentially pair programming but with more people involved. I've really enjoyed that process actually. I think it's actually a great way to experiment with different technologies because you get all of the minds together and it's a very good way to kind of transfer knowledge and explore things together but Woody Zuill talks about mob programming and he likes to ask the question, "Why did we begin doing mob programming for the team at Hunter Industries that originally started mob programming?"

People would give answers like, "Because it cuts out code review from the process because you have lots of eyeballs on it in real time," or, "Because it reduces bugs," or, "Because it gives you better quality code. It gives all the best ideas into the product in real time," and all those things are valid points that are really good benefits of mob programming. But he says those things may be true but actually, they're not why we tried mob programming. The reason we tried mob programming was because the team wanted to try it. That's a really important point.

The team needs to be experimenting with things that they're passionate about and they need to be exploring things on their own terms. But with that said, another lesson from that story of kind of his team at Hunter Industries discovering mob programming is that the team didn't discover mob programming in a vacuum. Really, the team discovered mob programming because the team became really excellent at experimenting and evaluating those experiments and then, they like to talk about this phrase that Kent Beck coined, 'turn up the good.' When something is working well, we often focus on the negative things and trying to eliminate those things but what happens if we take the things that are working well and 'turn that dial up to 11.'

CHARLES: Yeah, I love that. I remember in the kind of the original layout of extreme programming, talking about how I really just wanted to turn up all the things that were working for 11 or to 11, so testing, refactoring, incremental releases and things like that.

DILLON: Exactly.

CHARLES: I actually had one question that's maybe a little bit of a diversion. This is actually the first time I've heard of mob programming. It's definitely not the same sort of mob programming I learned about in Richard Garfield's paper. I think it was more referring to massively distributed open source in the form which is really kind of commonplace now that happens on GitHub. I think it's maybe, an obsolete definition of mob programming but how many people would be in a mob like two, three, four, five, six, seven, 10?

DILLON: That's a great question. Really, the answer is of course, it depends. That's a consultant's favorite answer but it really does. My rule of thumb is I find it usually three people is a very nice size for a mob. I find that mobs tend towards around three or four people but that being said, it's important to note that mob programming is all about this idea that what is the true cost of programming.

I think that often we look at programming as the act of writing code, initially and that's a very limited way of looking at coding. Because of course, 90% of our effort is spent maintaining code, making decisions around code, reproducing bugs, fixing bugs, communicating with customers about bugs -- bugs are extremely expensive -- the farther out they get, until eventually they get to the point of a customer discovering them, bugs are in extremely expensive part of software. If we can minimize bugs, that's very valuable.

When you look at programming on this bigger scale and look at the bigger picture of programming, then you realize that you may be able to get one person to write the code faster but then, that person needs to code review it. That person needs to go and ask somebody question down the line when they don't have context because they weren't involved in the decision making.

For example, maybe there's a UX person who doesn't have context on certain choices that were made, so there's a lot of churn, so you can kind of eliminate that churn by getting all the relevant people involved right away and that's the idea. In my experience with mob programming, it works really well to keep kind of a core of around three people. Sometimes, somebody goes up to have a conversation with somebody, take a break or answer somebody's question, maybe somebody from another team has a question that type of thing and so, the team can keep coding as a pair or whatever. But ultimately, the idea is that you get faster because you're building up this shared context and you're not spending as much time down the line answering questions, doing code reviews and things like that.

CHARLES: Right. I see.

DAVID: That kind of matches with my experience. Mob programming on previous teams, the way we had it set up is there was a regular mob programming chat session that the whole team was invited to but it was optional. You can just show up if you wanted to and really, that sort of made it so that there was a set of people who regularly attend -- three to five people in a session -- and they were the core group, essentially.

DILLON: Right. That's another great point. Invitation is a powerful technique. If you're kind of mandating the people try an experiment or work in a certain way, ultimately it's much more powerful to let the team experiment on their own and follow their passion and they'll discover great things. It's about experimenting, rather than choosing specific experiments.

While we're on this topic of kind of the real cost of coding, I think this is a good point to talk about this quality in Elm because, I think that this is one of the things that really motivates me to use Elm myself and introduce it to others is that, I think that Elm really get something about programming where there's a sort of superficial ease of certain techniques that Elm kind of goes beyond and says, "Actually, let's optimize for a different set of things that we think make code more maintainable and more delightful to work with in the long run."

CHARLES: I wanted to also transition between, we were on a little diversions on mob programming but do you use mob programming as explicit technique for introducing Elm when a team is considering adopting it?

DILLON: That's a fantastic question. I absolutely do. Of course, I honor the ways of working in a particular organization or team. I think that's important to do but I do strongly encourage using mobbing as a technique for knowledge sharing and when I'm on-site with a client, I find it extremely powerful as a technique for knowledge sharing and also, let's say you do an experiment, somebody is off in a corner and they're trying out Vue.js or they're trying out Elm or they're trying a particular coding technique. Then they come back to their team and they say, "Hey everybody, I tried this great thing," and now they have to spend this time convincing everybody and saying like, "Wait a minute. You didn't try this, you didn't try it that way. It wouldn't actually work in our context because of this." I think that it's very powerful to have everybody kind of involved in that process so that you can evaluate it together as a team.

CHARLES: Because the thing is like, when you experience win or you experience fail, it's a very visceral feeling and that's the thing that sells you or turns you away. You can argue until you're blue in the face but words have a very limited capacity to convince, especially when compared with like physical and emotional feeling. It sounds like you can get everybody to have that shared experience, whether for the good or for the bad, you're going to arrive at a decision, orders of magnitude more quickly. They have to rely in conviction of that decision spread around the team.

DILLON: Exactly. I think that hits the nail on the head and you say that we have this sort of skepticism of arguments from theoretical conversations, rather than 'show me the money,' but it's actually, try solving a real problem in this and that's exactly as it should be. I think that's one of the big antidote from this problem that I've seen in a lot of environments, where there's this analysis paralysis, especially with the state of the JavaScript ecosystem these days. I think that one of the keys to improving that situation is to get good at trying things, rather than theorizing about things.

We have a tendency to want to theorize and when we do that, then we say, "Can it solve this problem? Can it solve this problem? Can it solve that problem?" You can talk about that until the cows come home but it doesn't get you anywhere and it doesn't really convince anybody of anything. The key is to find very small experiments and what I really recommend and what I'm dead focused on when I'm initially working with a client is getting something into production.

Now, that doesn't mean that you need to have a road map for turning your entire application into Elm. In fact that's the whole point, is that you're not trying to do that. The point is you're trying to get as realistic of an experience as possible for what problems might occur if we do this? Will the team enjoy working with this language? Will it work well with our built pipeline? Will there be any unforeseen issues? You don't know until you actually try it, so you've got to try it and you've got to try it in tiny, tiny steps and low risk experiments.

CHARLES: Right but you've got to try it for real. You don't want to try it with a TodoMVC.

DILLON: Exactly. It needs to be meaningful, to really have a good understanding of what it's going to be like.

CHARLES: I would say that I tend to agree but I've definitely encountered the counterargument and I also think this counterargument makes sense or perhaps where the pushback lies is if I'm constantly experimenting, then what I'm doing is I'm internally fragmenting my ecosystem and there is power in similarity. Any time you introduce something different, any time you introduce one fragment, you're introducing complexity -- a mental complexity -- like maybe I have to maintain my Elm app and I also have to have my Legacy... Or not Legacy, I've got my other JavaScript tool kit that does it in one way. Maybe I've got a couple of more because I've run these other experiments. I'm not saying that there is one way but there is power in uniformity. There is power in diversity. Where do you find the balance?

DILLON: Those are all excellent points. To me, I think really the key is it's about the scientific method, you could say. The thing with the scientific method is that we often forget the last part. We get really good at hypothesizing about things. Sometimes people leave it at that, which we kind of just discussed. Sometimes, people go past the hypothesizing stage and they actually run the experiment and that's great. But then, the majority of people, if they get to that point, will forget to do the last step which is to evaluate the results.

I think the key here is you need to be experimenting and this is what it means for it to be a low risk experiment. It means that you're not setting yourself off in a direction where you can't turn back. You want to set it up in such a way that you can turn away from it with minimal cost. One of the things that is really helpful for that is if you build a tiny, independent, little widget in your application, try building that in Elm. Some people will do that with a little sort of login badge in the corner of their application.

One of the teams where I've introduced Elm at a Fortune 10 company, actually where we introduced Elm, we started out with just a tiny little table in one page and if we wanted to back that out, it would have been trivially easy but we decided that we wanted to go in further and invest more.

CHARLES: That makes a lot of sense. Effectively, you need to have a Plan B. Don't sync all of the available time that you have to invest in an experiment. Make sure that you have a Plan B and if you need to do this widget or this table in Angular or React or Ember or whatever, you are thinking about that -- how would that work.

DILLON: Exactly and the thing with experiments is the purpose of an experiment is not to build something. It's to learn. I really like this kind of ethos of lean startup, which I think is really getting much more into the mainstream in the software industry, which is a wonderful thing. The idea of lean startup, the kind of core concept is this idea of validated learning. Basically, in an environment where there's uncertainty, which is pretty much most of the things you're doing in software, the main goal is you're not shipping a product like you would be if you're trying to manufacture cars as quickly as possible. The main thing that you're producing is what they call 'validated learning' and so, you want to minimize the amount of time it takes to validate or invalidate your assumptions about something and then, you want to make it as cheap as possible to move on from that.

CHARLES: I like that. So if you're going to organize your development process around this principle or maybe not organize it but integrate it into development process, how do you know that you're conducting a healthy number of experiments, versus I may be conducting too many experiments? Is there a metric that you can look at? We need to have this many experiments running at all times or this is just too many or something else.

DILLON: That's a really interesting question. I think I would tend to think about that more again, as looking at the way the experiments are run, rather than 'are there too many experiments?' That's just not a problem that I've seen there being too many experiments. The pain that we tend to really see in environments where experiments are hurting teams is the way the experiments are being done. It's hard to backtrack from those experiments and as you were saying before, you kind of put yourself down this path where you can't walk it back and you create this sort of rift in the way the code is being written, which makes it more difficult to work in that codebase.

The thing with experiments is they can have really big payoff. Now, you want to make sure that you're not just going in and picking up every shiny object that you see. One thing that can keep you honest with that is if you're kind of coming up with a hypothesis before you start. If you're saying, "This is the value to our business and to our team if we attempt this thing and this is what will prove that it seems to have that value and this is what will tell us, 'Actually, it doesn't have that value and we should drop it and cut our losses.'"

CHARLES: That's a great heuristic. As you're saying and imagining how that might have saved my bacon in the past because I've definitely made the mistake of playing with too many shiny objects and picking things because I didn't fully evaluate what I thought the value. I was explicit with myself about what is the value that is going to bring to this project or this business. I have a theory about it but I am not thinking what is my hypothesis and how am I going to validate or invalidate? I'm thinking, I've got a short term pain that I'm experiencing and I'm grasping for this thing, which I think will solve it and I'm not properly evaluating how it's going to affect me long term.

DILLON: Right and that could be a great team practice to play around with is often, teams will kind of come up with action items out of retrospectives. One thing that I think can be really beneficial for teams is to kind of flip that notion of doing action items which again, it's really just doing the middle part of the experiment where you're conducting the test but you cut out the hypothesis part and the evaluation part. Try to bring that into your team's retrospective and try to have explicit hypotheses in the retrospectives and then, in the next retrospective, evaluate the results.

CHARLES: All right. I will definitely keep that in mind but this feels like a fresh take on kind of how you manage software development that I haven't encountered too much, being more scientific about it. It sounds like science-oriented development.

DILLON: Right.

DAVID: I like that.

DILLON: There are a lot of buzzwords these days in software development, in general and it's really becoming a problem, I think in the Agile community but really, what it boils down to is these basic elements and basing decisions on feedback is one of those fundamental unit. You can call the scientific method, you can call it lean startup and validated learning, you can call it agile, you can call it whatever you want but ultimately, you need to be basing things on feedback.

I think of it almost like our nerves. There's actually a disorder that some people have, which can be fatal, which is that their nerves don't tell them when they're feeling pain. I think this is a great analogy for software because that can happen to companies too. They don't feel the pain of certain decisions not landing well. Because they're not getting feedback from users, they're not getting feedback from metrics and recording, they're not getting feedback from doing that final evaluation step of their experiments, so when you fall on the ground, a small cut could be extremely harmful because you don't know the damage it's doing to you.

CHARLES: I think that is a good analogy. One of the things that I'm curious about is we've been discussing a lot of techniques for experimentation and how you can integrate that into your process and how you can make your experiments safe, so let's talk a little bit about -- first of all, two things -- why would I want to experiment with Elm in the first place? Because ultimately, that's why we're here and why we're having this conversation. What's compelling about it that would make me want to experiment? And then how can I begin to experiment with Elm?

DILLON: I actually just published a blog post yesterday. It's called 'How Elm Code Tends Towards Simplicity.' To your question of why would a team consider Elm, I kind of talk a little bit in this blog post about a case study at a Fortune 10 company where I introduced Elm to a few of the teams there. One of the teams there, we had actually seen an Angular project that they had worked on and often, in an enterprise environment, you have projects moving from one team to another.

I actually had my hands on this Angular project. It kind of moved over to another team and we were experiencing some major pain trying to make changes in this codebase. Even making the simplest change, we were finding that there were a lot of bugs that would be introduced because there's some global variable. There's some implicit state. Sometimes, it was even reaching in and tweaking the DOM and really, the topic of conversation at our team lunches was how afraid we were to touch this codebase.

Fast forward a few months and this team was asking my advice on picking a new frontend framework and I introduced them to Elm. They took a run with it and it was pretty remarkable to see this same team that had really struggled with AngularJS and they didn't really have a strong sense of what were the best practices. They weren't getting any guidance from the framework itself and the tooling around it and they actually loved the experience of working with Elm because they were saying, "This is amazing. Maybe it takes a little time to figure out how to solve a particular problem on Elm but once we do, we know that we've done it in a solid way."

One of the things that I think is most powerful about Elm is that it keeps you from shooting yourself in the foot. I think that's a really good headline kind of summary of what I love about Elm. For example, tweaking the DOM. Now, it might seem like a pretty obvious thing that we just won't tweak the DOM and that's fair enough. That might not be a problem for a lot of teams. People wouldn't even reach for that technique because they're disciplined about it. But at a certain point, you start taking on enough things and then go from kind of those basic things that are going to make your code more unreliable and unsafe like tweaking the DOM and you start getting into the realm of best practices.

There's so much discussion these days in the JavaScript community about best practices, which is great. It's great to discuss that but my concern is that there's a new best practice each week and the team has to agree on it, you have to find techniques for enforcing it, people have to make sure that these best practices are being followed in code reviews. Then when you look at a given piece of code, you have to trust that those best practices are being followed, so it requires a lot of work to make sure, in your reducers, in redux that you are not mutating anything. With Elm, data is just immutable. That's just how it is.

There are a lot of these kind of things that are baked into the language and the expressivity of the type system allows you to bake in your own constraints. One of the things that I find really compelling about Elm is its design really prevents you from shooting yourself in the foot and it gives you tools for making sure that you take it even a step further and it helps you enforce these best practices at a compiler level.

CHARLES: Now what's interesting here is it's almost like the opposite tension of experimentation is a work, right? like here, we have an example of uniformity being the more powerful track but then inside the actual macroscopic process, you want a lot of experimentation and diversity. But at the microscopic level, inside your application, it sounds like you want less experimentation and you derive a lot of strength from that but --

DILLON: That's a great point.

CHARLES: -- Experiments that are possible, yeah.

DILLON: I think that there is a lot of pain these days in the JavaScript community. We hear people talking often about JavaScript fatigue and it's a real thing. It takes a lot of work to stay on top of the latest best practices and frameworks and that can be a lot of fun. I love learning about the latest new frameworks and tooling but ultimately as you're saying, we don't want that experimentation so much about the fundamentals. We want some dependable, solid fundamentals and then we want the experimentation to happen within there. I think that's exactly what we see in the Elm ecosystem.

We have a single kind of data store or way of managing state in Elm. It's called the Elm Architecture. In fact, it's what Redux is based on and it worked extremely well and you don't have to experiment with different data stores in Elm because that's just what Elm code looks like. Now, if you want to experiment in Elm, then there is a lot of innovation happening. One of my favorite things about Elm is that the compiler and its expressiveness has sparked a lot of creativity. One of my favorite things about Elm is the library called Elm UI.

Actually, a client that I'm working with right now, it's a really interesting case study. They are kind of a very small startup. They just kind of branched off of a larger startup. They're building some tooling for this ecosystem. They were engineers at a company called Procore that does cloud document management for construction companies. They wanted to get a product-ready for a big conference for their potential clients. The reason they brought me in to help them was because they wanted to reach this ambitious target of being able to do a demo of this brand new product at this conference and they wanted to iterate very quickly. One of the things that really drew them into Elm in the first place is this library Elm UI.

Elm UI essentially, Richard Feldman gives a talk on it, where he uses the analogy of it being treating CSS and HTML as bytecode for your views. I think that's a really apt way to put it. If you break down this idea of CSS -- Cascading Style Sheets, it removes the cascading part of CSS and it removes the sheets part of CSS. What you're left with is a way of expressing style and it's a way of expressing style that is able to part ways with all of the baggage of the entire history of backwards compatible decisions that CSS has ever made.

If you want to vertically aligned something, then you just say, "Align vertically," you know, center vertically. If you want to center something horizontally, you say center X. It creates a high level language for expressing views. My experience with Elm UI, this may not be the right choice for every team but I love it. I use it on all of the projects that I maintain personally. I love using it because it gives you that same sense of invincibility refactoring that you get with Elm, which is remarkable that you could have that feeling with managing views.

CHARLES: It's definitely something that feels like a dark art and it can't be called science. It's an art. It's a science for some people but it's historically been a dark art and something fiddly to work with. In terms of being able to make the experiment with Elm, when we talked a little bit about why you might want to experiment with it in the first place, what the business case is, I guess my next question is or a question that immediately comes to mind is supposing that we have decided to experiment with this, how do you mitigate that experiment?

We talked about lowering the cost, having a way to turn away from it, having a way to make it inexpensive. For example, one of the things that I think of when evaluating a new technology is how well can I use it with old technologies. I have a lot about best practices in my tool bag. We all do. We got our all favorite libraries and pathways that are just familiar to us. One of the things that I've noticed is when adopting a new technology, one of the things that makes it easy to experiment with is how well it works with the existing technologies. I know that, we talked about Elm UI, kind of rethinking style in CSS and your views and Elm itself as a completely different language within JavaScript, that can be both liberating but it can also be limiting in the sense that I can't reach back for my existing tool if no tool exists in this new space.

The kind of experience that I've had where this is really worked is systems like JRuby or Clojure, where there's a very clear pathway to be able to use Java libraries from those environments, so you always have kind of an escape hatch. What's that like in Elm?

DILLON: This is a really interesting conversation because it highlights, in some ways some of the most defining features of Elm. In terms of how do you kind of pull Elm into an existing application, there are a lot of different techniques for that. It's pretty straightforward to create a little Elm app. We usually don't call them components for reasons that we can get into if we want to but that's a whole can of worms.

But if you've got a little Elm application that you want to use to render a widget on your page, then it's as simple as just calling Elm.yourmodule.init and rendering it onto the page there. That's quite straightforward and if you want to interface with your existing code there are several ways to do that. There's something called port in Elm, which is how you kind of communicate by sending these messages and data back and forth between your Elm app and JavaScript.

Now, this is one of the decisions, I think that defines Elm as the language and the reason this is important is because Elm decided not to make the choice that a lot of other compile to JS languages do. For example, if you look at ReasonML or PureScript or a more extreme example, TypeScript. TypeScript is a superset of JavaScript, so it's trying to allow you to gradually introduce this to get some incremental improvements for your JavaScript code, so it's extremely easy to experiment with it, which we've talked about the importance of experimentation.

Now, the challenge with this technique, the tradeoff here is it's great, that it then becomes very easy to transition into it and that's an excellent strategy for the goals of TypeScript. Elm has a different set of goals, so the things that elm is focused on giving you is a truly type-safe experience. When you're working with Elm, if your Elm code says that this data is a float, then it is a float. Either, it is a float or that code is not being run and so, that's very different than the experience in TypeScript where you have these escape hatches.

This is an inevitable choice for any compiled to JS language. Are you going to have escape hatches or not? Elm is really the only language out there, I think that chooses not to have escape hatches and that is actually the thing that that I love about the language because that's the only way you can truly have guarantees, rather than, "Yeah, I'm pretty sure that these type guarantees hold."

DAVID: Yeah, wishes and dreams.

DILLON: Yeah.

CHARLES: What does it mean to have no escape hatches? because you talked about ports. Does it mean like it's impossible to use an external JavaScript library?

DILLON: That's an excellent question. You absolutely can use JavaScript libraries. It means that it's being explicit and upfront about the fact that there's uncertainty in these areas. That's what it comes down to. Take for example dealing with JSON. In a JavaScript application, what we get when we're dealing with JSON is you make a request up to the server, you have some callback that passes in the data you get back and then you start pulling bits and pieces off of it and you say 'response.users subzero.firstname' and you hope that none of those things are null, none of those types are different than what you expected.

In a way, it's kind of letting you pretend that you have certainty there when in fact, you don't and with Elm, the approach is quite different. You have to explicitly say, "I expect my response to have this shape. I expect it to be a list of things, which have a first name and last name which are strings," and then Elm says, "Okay, great. I'm going to check your assumptions," and if you're right, then here you go and you're in a well typed-space where you know exactly what the types are and if you're wrong, then that's just another type of data, so it's just a case statement where you say, "If my assumptions were correct, then do something and if my assumptions were incorrect, then you decide what to do from there."

CHARLES: Right. For me, it sounds like there is some way because ultimately, I'm going to be getting unstructured but I'm going to be getting JSON back from the server and maybe, I have some library that's going to be doing that for me and enhancing it and adding value to that JSON in some way. But then at some point, I can present it to Elm but what you just saying is I need to be complete in making sure that I handle each case. I need to do or handle the case. Explicit about saying if the assumptions that Elm wants to make, turn out to not be true, Elm is going to make me handle the case where those assumptions were not true.

DILLON: Exactly. I think that TypeScript of any type is the perfect illustration of the difference. TypeScript of any type is sort of allowing you to say, "Don't type check this. Trust me here," and Elm's approach is more kind of just be explicit about what you want me to do if your assumptions are incorrect. It doesn't let you kind of come in and say, "No, I know I'm going to be right here."

CHARLES: Right but there is a way to pass data structures back and forth.

DILLON: There absolutely is and actually, there's a technique that's starting to gain some traction now, which I'm really excited about, which is rather than using this sort of JavaScript interrupt technique we talked about, which is again, it's very much like communicating with a server where you're kind of sending messages and getting data back -- getting these messages with data back. But there's an alternative to that which is using web components. Actually, there's quite good support for assuming that you don't need to be compatible with Internet Explorer.

Basically in a nutshell, if you can wrap a sort of declarative web component around anything, it could be a Google Maps API, it could be a syntax highlighting JavaScript library, something that you don't have an Elm library for but you want to use this JavaScript library, it's actually quite a nice experience. You just render that custom element using your Elm code just as you would any other HTML in Elm.

CHARLES: Yeah I like that, so the HTML becomes the canvas or composition with other JavaScript and the semantics are very well-defined and that interface is actually pretty thin.

DILLON: Exactly and the key again is that you wanted to find a declarative interface, rather than an imperative one where you're kind of just doing a series of statements where you say, "Do this and then set this value and then call this and then set this call back." Instead, you're saying, "Render this Google Maps custom element," which is centered around these coordinates and has this zoom level on. You declaratively give it the bit of information that it needs to render a particular view.

CHARLES: Okay. Then I guess the final question that I have around this area is about being able to integrate existing tools and functions inside of an Elm application. Because it sounds like you could theoretically develop large parts of your application, is there a way that you can actually have other areas of your application that are not currently invested in Elm still benefit from it, in the sense for kind of need of JavaScript APIs that Elm can make available.

DILLON: Right, so you're kind of talking about the reverse of that Elm reaching out to JavaScript. You're asking about, can JavaScript reach out to Elm and benefit from some of its ecosystem?

CHARLES: Exactly. I say that is that another potential vector for experimentation.

DILLON: It's a really interesting thought. I haven't given it too much thought, to be honest but I actually have heard it come up before and my gut feeling is that it's probably more fruitful to explore the inverse, reaching out to JavaScript from Elm and the reason is kind of the main appeal of Elm is that when you're operating within Elm, you have this sense that if it compiles, it works. Because again, this central decision to not allow escape hatches is what allows you to have that sort of robustness, so you have this feeling of bullet proof refactorings and adding new features seamlessly where you change your data modeling to say, "Here's this other case that can be represented," and then suddenly, the Elm compiler says, "Tell me what to do here, tell me what to do here and tell me what to do there," and you do it and your app is working. That's the real appeal of Elm, I think and you don't really get much of that by just calling out to an Elm library from within JavaScript. That's my gut feeling on it.

CHARLES: Okay, that's fair enough. On the subject of interrupt and using tools like JSON, you actually maintain a GraphQL library for Elm. You probably have a lot of experience on this. Maybe we can talk about that as a concrete case that highlights the examples.

DILLON: Yeah. I think to me this is one of the things that really highlights the power of Elm, to give you a really amazing refactoring and kind of feature creating experience. A lot of Elm libraries are prefaced by the author name, so it's still DillonKearns/ElmGraphQL. I spoke about it this year at ElmConf.

In a nutshell, what it does is it actually generates code based on your GraphQL schema. For anyone who doesn't know, GraphQL is just kind of a language for expressing the shape of your API and what types of data can return. What DillonKearns on GraphQL does is it looks at your GraphQL schema and it generates an API that allows you to query that API. using this library, you can actually guarantee that you're making a valid query to your server. Again, you get this bulletproof experience of refactoring in Elm where you can do something like make a change in your API and recompile your Elm code and see whether you've made a backwards incompatible change.

All of this effort of doing sort of this JSON decoding I was talking about earlier where you kind of have to explicitly say, "These are my assumptions about the shape of the JSON that I'm getting back." When you're using this library, you no longer need to make any assumptions because you're able to rely on this sort of schema of your API and so you know when you're requesting this data, you don't have to run it, see if it works and then tweak it and run it again -- this sort of cycle of checking your assumptions at runtime.

It moves those assumptions that you're making from runtime to compile time and it can tell you when you compile your application, it can say, "Actually, this data you're requesting, it doesn't exist," or, "It's actually called this," or, "This is actually the type of the data."

CHARLES: Right. I love that. How do you do that? Because it seems like you've got a little bit of a chicken and the egg problem because the schema is defined outside of Elm, so you have to be able to parse and understand the schema in order to generate the Elm types to be able to compile Elm code against them. Maybe I'm not --

DILLON: That's exactly right. That's exactly what it does. Now, the nice thing is that GraphQL is really designed for these types of use cases. It supports them in a first class way. If you have a GraphQL API, that means you have built into it whether you know about it or not, a way to introspect the schema. All of the queries for kind of interrogating that GraphQL server and asking what types of data does this return, what are all your queries that I can run, it's built into it by the framework, so that comes for free. Getting up and running with this package I built is as simple as running a little npm CLI, pointing it to either your URL for your server or the JSON form of your schema, if you prefer and then, it generates the code for you.

CHARLES: Wow, that sounds fantastic. This is the exact kind of thing that feels like it would be cool if I could just start using this library to manage the GraphQL of my application but I'm consuming that GraphQL from other JavaScript but it's the Elm code that's managing it. Do you see what I mean?

DILLON: I hadn't considered that. I guess you could. You're right. Maybe I’m so smitten with Elm that it's hard to see an in-between but I guess, you could get some benefits from that approach.

CHARLES: Right and as an experiment of course.

DILLON: There you go. There you go.

CHARLES: All right. With that, I think we'll wrap it up. Thank you so much, Dillon for coming on and talking with us on the podcast.

DILLON: My pleasure. I really enjoyed the conversation.

CHARLES: I actually got so many great tidbits from so many different areas of software development in Elm but also, just in kind of other things that I'm interested in trying. It was a really great conversation.

DILLON: I had a lot of fun and I love discussing these things. For any listeners who are interested in this stuff, feel free to reach out to me on the Elm Slack or on Twitter. I'm at @DillonTKearns. I'm also offering a free intro Elm talk for any companies that are kind of entertaining the idea of doing an experiment with Elm. If you go to IncrementalElm.com/Intro, you can find out about some of the talks that I'm offering.

CHARLES: All right. Well, thank you very much and we, as always are the Frontside. We build software that you can stake your future on and you can get in touch with us at @TheFrontside on Twitter or Contact@Frontside.io on email. Please send us any questions you might have, any topics that you'd like to hear about and we look forward to hearing from you and we will see you next week.