382: Domain-Specific Languages
Episode 382 · May 2nd, 2023 · 36 mins 9 secs
About this Episode
Joël has been integrating a third-party platform into a testing pipeline...and it has not been going well. Because it's not something she usually keeps up-to-date with, Stephanie is excited to learn about more of the open-source side of things in Ruby, what's new in the Ruby tooling world, and what folks are thinking about regarding the future of the language.
Today's topic is inspired by an internal thoughtbot Slack thread about writing a custom matcher for Rspec. Stephanie and Joël contrast DSLs vs. Object APIs and also talk about:
- CanCanCan vs Pundit
- RSpec DSL
- When is a DSL helpful?
- Why not use both DSLs & Object APIs?
- When does a DSL become a framework?
This episode is brought to you by Airbrake. Visit Frictionless error monitoring and performance insight for your app stack.
- RubyKaigi 2023
- Mystified by RSpec’s DSL? by Jason Swett
- Building Custom RSpec Matchers with Regular Objects
- Writing a Domain-Specific Language in Ruby by Gabe Berke-Williams
- Acceptance Tests at a Single Level of Abstraction
- Discrete Math and Functional Programming
STEPHANIE: Hello and welcome to another episode of The Bike Shed, a weekly podcast from your friends at thoughtbot about developing great software. I'm Stephanie Minn.
JOËL: And I'm Joël Quenneville. And together, we're here to share a little bit of what we've learned along the way.
STEPHANIE: So, Joël, what's new in your world?
JOËL: I've been integrating a third-party platform into our testing pipeline for my client. It has not been going well. We've been struggling a little bit, mostly just because tests just kind of crash. Our testing pipeline is pretty complex. It's a lot of one script, some environment variables, does a few things, shells out to another script, which is in a different language. Does a few more things, shells out to another script, maybe calls out to rake, calls out to a shell script. There are four or five of these in a chain, and it's a bit of a mess.
Somewhere along in there, something is not compatible with this third-party service that we're trying to integrate with. I was pairing this week with a colleague. And we were able to reproduce a situation where we were able to get a failure under some conditions and a success under other conditions. So these are basically, if we run the whole chain of scripts that call each other from the beginning, we know we get a failure. And if we skipped entirely the chain of scripts that set up things and then just manually try to invoke a third-party service, that works.
And so now we know that there's something in between that's incompatible, and now it's just about narrowing things down. There are a few different approaches we could take. We could try to sort of work our way forward. We know a known point where it breaks and then just try to start the chain one step further and see where it fails. We could try to get fancy and do a binary search, like split it in half and then half and half again.
We ended up doing it the other way, where we started at the end. We had our known good point and then just stepping one step back and saying, okay, now we introduce the last script in the chain. Does that work? Okay, that pass is great. Let's go one step further; two scripts up in the chain. And at some point, we find, okay, here's the one script that fails. Now, what is it within this script? And it was a really fun debugging session where we were just narrowing things down until we found the source of the bug.
STEPHANIE: Wow, that sounds pretty complicated. It just seems like there are so many layers going on. And it was really challenging to pinpoint where the source of the issue was.
JOËL: Definitely. I think all the layers made it really complicated. But having a process that we could follow and then kind of narrowing it down made it almost mechanical to figure out where the bug was once we got to a point where we had a known good point and a known bad point.
STEPHANIE: Yeah, that makes sense. Kind of sounds like if you are using git bisect or something like that to narrow down the scope of where the issue could be. I'm curious because this is like a bunch of shell scripts and rake tasks or commands or whatever. What would have made this debugging process easier?
JOËL: I think having fewer scripts in this chain.
STEPHANIE: [laughs] That's fair.
JOËL: We don't need so many scripts that call out to each other in different languages trying to share data via environment variables. So we've got a bit of a Rube Goldberg machine, and we're trying to patch in yet another piece in there.
STEPHANIE: Yeah, that's really tough. I was curious if there was, I don't know, any logging or any other clues that you were getting along the way because I know from experience how painful it is to debug that kind of code.
JOËL: It's interesting because I feel like normally logging is something that's really useful. In this particular case, we run into an exception at some point. So it's more of under what conditions does the exception happen? The important thing was to find that there is a point where it breaks, and there's a point where it doesn't, and realizing that if we ran some of these commands just directly without going through the whole pipeline, that things did work and that we were not triggering that exception.
So all of a sudden, now that tells us, okay, something in our pipeline is wrong. And then we can just start narrowing things down. So yeah, adventures in debugging. Sometimes it's really frustrating, but then when you have a good process, and you find the bug, it's incredibly satisfying.
STEPHANIE: I like that you used a process that can be applied to many different problems, in this particular case, debugging a testing pipeline. Maybe not something that we do every day, but certainly, it comes up, and now we have tools to address those kinds of issues as well.
JOËL: So my week has been up and down with all of this debugging. What's been new in your world?
STEPHANIE: I've been doing some travel planning because I'm going to RubyKaigi in Japan.
STEPHANIE: This is actually going to be my first international conference, so I'm really looking forward to that. I just have never been compelled to travel abroad to go to a tech conference. But I'm really looking forward to going to RubyKaigi because now I've been to the U.S.-based conferences a few times. And I'm excited to see how things are different at an international conference and specifically a RubyKaigi because, obviously, there's a lot of really cool Ruby work happening over there in Japan.
So I'm excited to learn about more of the open-source side of things of Ruby, what's new in the Ruby tooling world, and just what folks are thinking about in terms of the future of the language. That's not something I normally keep super up-to-date on. But I'm excited to be around people who do think and talk about these things a lot and maybe get some new insights into my own work.
JOËL: Do you find that you tend to keep up more with some of the frameworks like Rails rather than the underlying language itself?
STEPHANIE: Yeah, that's a good question. I do think because the framework changes a little more frequently, new releases are kind of more applicable to the work that I'm doing. Whereas language updates or upgrades are a little bit less top of mind for me because the point is that it doesn't have to change [laughs] all that much, and we can continue to work with things as expected and not be disrupted.
So it is definitely like a whole new world for me, but I'm really looking forward to it. I think it will be really interesting and just kind of a whole other space to explore that I haven't really because I've usually been focused on more of the web development and industry work side of things.
JOËL: What's a Ruby feature that either is coming out in the future or that came out in the last couple of releases that got you really excited?
STEPHANIE: I think the conversation about typing in Ruby is something that has been on my radar but has also been ebbing and flowing over time. And I did see a few talks at RubyKaigi this year that are going to talk about how to introduce gradual typing in Ruby. And now that it has been out for a little bit and people have been using it, how people are feeling about it, pros and cons, and kind of where they're going to take it or not take it from there.
JOËL: Have you done much TypeScript?
JOËL: Types definitely, I think, change the way you think about code; at least, that's been my experience.
STEPHANIE: Yeah, absolutely. I haven't gotten the pleasure to work with types in Ruby just yet, but I've just heard different experiences. And I'm excited to see what experts have to say about it.
JOËL: That's the fun of going to a conference.
STEPHANIE: Absolutely. So yeah, if any listeners are also headed to RubyKaigi, yeah, look out for me.
JOËL: I was recently having a conversation with someone about the fact that a lot of languages provide ways to sort of embed many languages within them. So the Lisp family of languages are really big into macros and metaprogramming. Some other languages are big into giving you the ability to build your own ASTs or have really strong parsing capabilities so that you can produce your own, again, mini-language.
And Ruby does this as well. It's pretty popular among the Ruby community to build DSLs, Domain-Specific Languages using some of Ruby's built-in abilities. But it seems to be a sort of universal need or at the very least a universal desire among programmers. Have you ever found yourself as a code author wanting to embed a sort of smaller language within your application?
STEPHANIE: I don't think I have, to be honest. It's a very interesting question. Because I think the motivation to build your own mini-language using Ruby would have to be you'd have to have a really good reason for it, and in my experience, I haven't quite encountered that yet. Because, yeah, it seems like a lot of upfront work, a lot of overhead to introduce something like that, especially if it's not necessarily either a really, really particular domain that others might find a use for, or it just doesn't end up seeming worthwhile if I can just write regular, old Ruby code.
JOËL: I think you're not alone. I think the Ruby community has been kind of a bit of a pendulum here where several years ago, everything that could be made into a DSL was. Now the pendulum kind of has been swinging the other way. And we see DSLs, but they're not quite as frequent. For those who maybe have not experienced a DSL or aren't quite familiar with the concept, how would you describe the idea?
STEPHANIE: I think I would describe domain-specific languages as a bit of a mini-language that is created for a very particular problem space in mind to make development for that domain easier. Oftentimes, I've also kind of seen people describe the benefit of DSLs as being able to read that language as if it were plain English.
And so, in my head, I have kind of, at least in the Ruby world, right? We see that a lot in different gems. RSpec, for example, has its own internal DSL, and many people really enjoy it because it took the domain of testing. And the way you write it kind of is how you might read or understand it in English. And so it's a bit easier to talk about what you're expecting in your tests.
JOËL: Yeah, it's so high-level and minimal and domain-specific that it almost stops feeling like it's a programming language and can almost feel like it's a high-level configuration for this very particular domain, sometimes even to the point where the idea is that a non-programmer could read it and understand what's going on.
STEPHANIE: I think RSpec is actually one of the first Ruby DSLs that you might encounter when you're learning Ruby for the first time. And I've definitely seen developers who are new to Ruby, you know, they're writing code, and they're like, okay, I'm ready to write a test now. And the project uses RSpec because that's what most of us use in our Rails applications. And then they see, like you said, almost a configuration language, and they are really confused. They're not really sure what they're reading. They struggle with the syntax a lot. And it ends up being a point of frustration when they're first starting out if they're not just copying and pasting other existing RSpec tests. I'm curious if you've seen that before.
JOËL: I've definitely seen that. And it's a little bit ironic because oftentimes, an argument for DSL is that it makes things simpler that you don't even have to know Ruby; you can just write it. It's simpler. It's easier to write. It's easier to understand. And to a certain extent, maybe that's true. But for someone who does know Ruby and doesn't know your particular little domain language, now they're encountering something that they don't know. And they're having to learn it, and they're having to struggle with it. And it might behave a little bit weirdly compared to how Ruby normally works. And so sometimes it doesn't make it easier for adoption. But it does look really good in a README.
STEPHANIE: That's totally fair. I think the other thing that's interesting about RSpec is that a lot of it is really just stylistic. I actually read a blog post by Jason Swett and the headline of it was "Mystified by RSpec's DSL? Some parentheses can add clarity." And he basically goes on to tell us that really RSpec is just leaning on some of Ruby's syntactic sugar of omitting parentheses for method calls. And if you just add the parentheses back in your it blocks or your describes, it can read a lot more like regular Ruby. And you might have a better time understanding what's going on when you realize that we're just passing our descriptors as arguments along with some blocks.
JOËL: That's ironic given that oftentimes, the goal of these is to make it look like not Ruby.
STEPHANIE: I agree; it is ironic. [laughs]
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JOËL: I think another drawback that I've seen with DSLs is that they oftentimes are more limited in their capabilities. So if the designer of the gem didn't explicitly think of your use case, then oftentimes, it can be really hard to extend or to support edge cases that are not specifically designed for that language in the way that plain Ruby is often much more flexible.
STEPHANIE: Yeah, that's really interesting because when a gem does have some kind of DSL, a lot of effort probably went into making that the main interface that you would work with or you would use. And when that isn't working for your use case, the design of the underlying objects may or may not be helpful for the changes that you want to make.
JOËL: I think it's interesting that you mentioned the underlying objects because those are often sort of not meant for public consumption when you're building a gem that's DSL forward. I think, in many cases, my ideal gem would make those underlying objects the primary interface and then maybe offer DSL as a kind of nice-to-have layer on top for those situations that maybe aren't as complex where writing things in the domain language might actually be quite nice. But keeping those underlying objects as the interface, it's nice to use and well-documented for the majority of people.
STEPHANIE: Yeah, I like that too because then you can get the best of both worlds. So speaking of trying to make a DSL work for you, have you ever experienced having to kind of work around the DSL to get the functionality you were hoping to achieve?
JOËL: So I think we're talking about the idea of having both a DSL and the underlying objects. And RSpec is a great example of this with their custom matchers. RSpec itself is a DSL, but then they also offer a DSL to allow you to create custom matchers. And it's not super well documented. I always forget how to define them, and so I oftentimes don't bother. It's just kind of too much of a pain for something that doesn't always provide that much value. But if it were easy, I would probably do it more. Eventually, I realized that you could use just regular Ruby objects as custom matchers. And they just seemed to respond to certain methods, just regular old objects and polymorphism.
And all of a sudden, now I'm back into all of the tools and mechanisms that I am familiar with, like the back of my hand. I can write objects all day. I can TDD them. I can apply any patterns that I want to if I'm doing something really complicated. I can extract helpers. All of that works really well with the knowledge that I already have without having to sink a lot of time into trying to learn the built-in DSL.
So, for the most part, now, when I define custom matchers, I'll often jump directly to creating a regular object and making it conform to the matcher interface rather than relying on the DSL for that. So once we go back to the test, now we're back in DSL land. Now we're no longer talking in terms of objects so much. We'll have some nice methods and they will all kind of read like English. So to pull a recent example that I worked on, I might say something like expect this policy object method to conform to this truth table.
STEPHANIE: That's a really interesting example. It actually kind of sounds like it hits the sweet spot of what you were describing earlier in the sense that it has a really nice DSL, but also, you can create your own objects, and that has an interface that you can implement. And yes, have your cake and eat it too. [laughs] But the idea that then you're kind of converting it back to the DSL because that is just what we know, and it has become so normalized.
I was talking earlier about okay; when is a DSL worthwhile? When is the use case a good reason to implement it? And especially for gems that I think that are really popular that we as a Ruby community have collectively used most of the time on our projects because we have oftentimes a lot of the same problems that we're solving. It seems like this has become its own shared language, right?
JOËL: Yeah, there are definitely some DSLs that we all end up learning because they're just so prominent in the Ruby community, even Rails itself ships with several built-in DSLs.
STEPHANIE: Yeah, absolutely. FactoryBot is another one, too. It is a gem by thoughtbot. And actually, in preparation to talk about DSLs with you today, I scoured our blog and found a really great blog post, "Writing a Domain-Specific Language in Ruby" by Gabe Berke-Williams. And it is basically like, here's how to write something like FactoryBot and creating your own little mini Ruby DSL for something that would be very similar to what FactoryBot does for fixtures.
JOËL: That's a great resource, and we'll make sure to link that in the show notes. We've been talking about some of the limitations of DSLs or some aspects of them maybe that we personally don't like. What are maybe examples of DSLs that you do enjoy working with?
STEPHANIE: Yeah, I have an example for this one. I really enjoy using Capybara's DSL for acceptance testing. I did have to go down the route of writing some custom selectors for...I just had some HTML elements within kind of a complicated table and was trying to figure out how to write some selectors so that I could write the test as if it were in, you know, quote, unquote, "plain English" like, within this table, expect some value.
And that was an interesting journey. But I think that it really helped me have a better understanding of accessibility of just the underlying building blocks of the page that I was working with. And, yeah, I really appreciate being able to read those tests from a user perspective and kind of know exactly what they're doing when they're interacting with this virtual browser without having to run it in headful mode and see it for myself.
JOËL: It's always great when a DSL can give you that experience of abstracting enough to where it makes the code delightful to work with while also not having too high a cost to learn or being too restrictive in what it allows you to do. Would you make a difference between something that's a DSL versus maybe just code that's written at a higher level of abstraction?
So maybe to get back to your example with Capybara, it's really nice to have these nice custom matchers and all of these things to work with HTML pages. If I'm writing, let's say, a helper method at the bottom of a test, I don't think that feels quite like it's a DSL yet. But it's definitely a higher level than specifying CSS selectors. So would you make a difference between those two things?
STEPHANIE: That's a good question. I think it's one of those you know it when you see it kind of questions because it just depends on the amount of abstraction, like you mentioned, and maybe even metaprogramming. That takes something from the core language to morph into what you could qualify as a separate language. What do you think about this?
JOËL: Yeah, part of me almost wonders if this exists kind of on a continuum, and the boundary might be a little bit fuzzy. I think there might be some other qualifications that come with it as well. Even though DSLs are typically higher-level helpers, it's usually more than just that. There are also sort of slightly different semantics in the way that you would tend to use them to the point where while they may be just Ruby methods, we don't use them like Ruby methods, and even to the point that we don't think of them as Ruby methods.
To go back to that article you mentioned from Jason, where just reminding people, hey, if you put params on this, all of a sudden, it helps you remember, oh, it's just a Ruby method instead of being like, oh, this is a language keyword or something.
STEPHANIE: Yeah, I wonder if there's also something to the idea of domain specificity where it should be self-service within the domain that you're working. And then it has limitations once you are trying to do something separate from the domain.
JOËL: Right, it's an element of focus to this. And I think it's probably also a language is not just one helper; it's a collection typically. So it's probably a series of high-level helpers, potentially. They might not be methods, even though that is ultimately one of the primary interfaces we use to run code in Ruby. So it's a collection of methods that are high-level, but the collection itself is focused. And oftentimes, they're meant to be used in a way where it's not just a traditional method call.
STEPHANIE: Right. There's some amount of you bringing to the table your own use case in how you use those methods.
JOËL: Yeah, so it might be mimicking a language keyword. It might be mimicking the idea of a configuration. We see that a little bit with ActiveRecord and some of the, let's say, the association and validation APIs. Those kind of feel like, yes, they're embedded in a class, but they feel like either keywords or even just straight-up configuration where you set key-value pairs of things to configure how a particular class is going to work.
STEPHANIE: Yeah, that's true for a lot of things in Rails, too, if we're talking about routes and initializers as well.
JOËL: So I've complained about some things I don't like about DSLs. I really like the routing DSL in Rails.
STEPHANIE: Why is that?
JOËL: I think it's very compact and readable. And that's an element that's really nice about DSLs is that it can make things feel very readable and, oftentimes, we read code more often than we write it. And routes have...I was going to say fewer edge cases, but I have seen some really gnarly route files that are pretty awful to work with, especially if you're mostly writing RESTful controllers, and I would recommend that people do. It's really nice to just be able to skim through a route file and be like, oh, these are the resources in my app and the actions I can do on each resource. And here are the ones that are nested.
STEPHANIE: Yeah, it almost sounds like a DSL can provide guardrails towards the recommended way of tackling that particular domain. The routes DSL really discourages you from doing anything too complicated because they are encouraging you to follow the Rails convention. And so I think that goes back to the specificity piece of if you've written a DSL, it's because you've thought very deeply about this particular domain and how common problems show up and how you would want people to be empowered by the language rather than inhibited by it.
JOËL: I think, thinking more about that, the word that comes to mind is declarative. When you read code that's written with DSLs, typically, it's very declarative. It's more just describing a thing as opposed to either procedural, a series of commands to do, or even OO, where you're composing objects and sending messages to each other. And so problems that lend themselves to being implemented through more descriptive and declarative approaches probably are really good candidates for a DSL.
STEPHANIE: Yeah, I like that a lot because when we talk about domains, we're not necessarily talking about a business domain, which is kind of the other way that some folks think about that word. We're talking about a problem space. And the idea of the language being declarative to describe the problem space makes a lot of sense to me because you want it to be flexible enough for different use cases but all within the idea of testing or browser navigation or whatever.
JOËL: Yeah. I feel like there's a lot of... there are probably more problems that can be converted to declarative solutions than might initially kind of strike you. Sometimes the problem isn't quite as bounded. And so when you want customizations that are not supported by your DSL, then it kind of falls apart. So I think a classic situation that might feel like something declarative is authorization.
Authorization are a series of rules for who can access what, and it would seem like this is a great case for a DSL. Wouldn't it be great to have just one file you can just kind of skim, and we can just see all of the access rules? Access rules that are basically asking to be done declaratively. And we have gems like that. The original CanCan gem and then the successor CanCanCan are trying to follow that approach. Have you used either of those gems?
STEPHANIE: I did use the CanCanCan gem a while ago.
JOËL: What was your experience with that style of authorization?
STEPHANIE: It has been a while but I do remember having to check that original file of like all the different authorizations kind of repeatedly coming back to it to remember, okay, for this rule, what should be allowed to happen here?
JOËL: So I think that's definitely one of the benefits is that you have all of your rules stored in one place, and you can kind of scan through the list. My experience, though, is that in practice, it often kind of balloons up and has all of these edge cases in it. And in some earlier versions, I don't know if that's still a problem today, it could even be difficult to accomplish certain things.
If you're going to say that access to this particular object depends not on properties of that object itself but on some custom join or association or something like that, that could be really clunky to do or sometimes impossible depending on how esoteric it is or if there's some really complex custom logic to do. And once you're doing something like that, you don't really want to have that logic in your...in this case, it would be the abilities file but inside because that's not really something you express via the DSL anymore. Now you're dropping into OO or procedural world.
STEPHANIE: Right. It seems a bit far removed from where we do actually care about the different abilities, especially for one-off cases.
JOËL: That is interesting because I feel like there's a bit of a read-versus write-situation happening there as well. It's particularly nice to have, I think, everything in one abilities file for reading and for auditing. I've definitely been in code where there's like three or four ways to authorize, and they're all being used inconsistently, and that's not nice at all.
On the other hand, it can be hard with DSL sometimes to customize or to go beyond the rules that are built in. In the case of authorization, you've effectively built a little mini-rules engine. And if you don't have a good way for people to add custom rules without just embedding procedural code into your abilities file, it's going to quickly get out of hand.
STEPHANIE: Yeah, that makes sense. On the topic of authorization, you did mention an example earlier when you were writing a policy object.
JOËL: I've generally found that that's been my go-to pattern for authorization. I enjoy the Pundit gem that provides some kind of light scaffolding around working with policy objects, but it's a general pattern, and you can absolutely write your own. You don't need a gem for that. Now we're definitely not in the DSL world. We're not doing this declaratively. We're leaning very heavily on OO and saying we're just going to create objects. They talk to each other. They can do anything that any Ruby object can do and as simple or as complex as they need to be.
So you have the full power of Ruby and all the patterns that you're used to using. The downside is it is a little bit harder to read and to kind of just audit what's happening in terms of permission because there's no high-level overview anymore. Now you've just got to look through a bunch of classes. So maybe that's the trade-off, flexibility, extensibility versus more declarative style and easy overview.
STEPHANIE: That makes a lot of sense because we were talking earlier about guardrails. And because those boundaries do exist, that might not give us the flexibility we want compared to just writing regular Ruby objects. But yeah, we do get the benefit of, like you said, auditing, and at least if we don't try to do some really gnarly, custom stuff, [laughs] something that's easier to read and comprehend.
JOËL: And, again, maybe that's where in the best of both worlds situation, you say, hey, I'm creating some form of rules engine, whether it's for describing routes, or authorization, permissions, or users can build custom business rules for a product or something like that. And it's all object-based under the hood. And then, we provide a DSL to make it nice to work with these rules.
If a programmer using our gem wants to write a custom rule that just really extends what the ones we shipped can do, allow them to do that via the object API. We have all the objects available to you that underlie the DSL. Add more rules yourself. And then maybe those can be plugged back into the DSL like we saw with the RSpec and custom matchers. Or maybe you have to say, okay, if I have a custom rule object, now I have to just stay in the object space. And I think both of those solutions are okay. But now you've sort of kept those two worlds separate and still allowed people to extend.
STEPHANIE: I like that as contributing to the language because language is never static. It changes over time. And that's a way that people can continue to evolve a language that may have been originally written at a certain time and place.
JOËL: Moving on from DSLs, we got some listener feedback recently from James, who was listening to our episode on discrete math. And James really appreciated the episode and wanted to share a resource with us. This is the book "Discrete Math and Functional Programming" by Thomas VanDrunen. It's an introduction to discrete math as a theoretical concept taught side by side with the very practical aspect of learning to use the language standard ML, and both of those factor into each other.
So you're kind of learning a little bit of theory and some practice, at the same time, getting to implement some discrete math concepts in standard ML to get a feel for them. Yeah, I've not read this book, but I love the concept of pairing a theoretical piece and a practical piece. So I'll drop a link to it in the show notes as well. Thank you, James.
STEPHANIE: Yeah, thanks, James. And I guess this is just a little reminder that if our listeners have any feedback or questions they want to write in about, you can reach us at firstname.lastname@example.org.
JOËL: On that note. Shall we wrap up?
STEPHANIE: Let's wrap up. Show notes for this episode can be found at bikeshed.fm.
JOËL: This show has been produced and edited by Mandy Moore.
STEPHANIE: If you enjoyed listening, one really easy way to support the show is to leave us a quick rating or even a review in iTunes. It really helps other folks find the show.
JOËL: If you have any feedback for this or any of our other episodes, you can reach us @_bikeshed, or you can reach me @joelquen on Twitter.
STEPHANIE: Or reach both of us at email@example.com via email.
JOËL: Thanks so much for listening to The Bike Shed, and we'll see you next week.
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