: Ruby, Python, Perl, PHP), but probably not in C or Java. Hence, modifying the DSL (let alone writing your own) is considerably harder. I’ll come back when I can. In a nutshell, declarative programming consists of instructing a program on what needs to be done, instead of telling it how to do it. Occasionally a nice balance between flexibility and general purpose use arises, and that language becomes popular. If FILTER is not empty, we will iterate through the categories of the product until we find one that is contained within FILTER. In a real application, DATA will be generated dynamically from a database query. For those who are still with me, I would like to go back to the main claim of this section, which is that a dsDSL has the advantages of both the high and the low level: But how is this truly different from purely imperative code? I would like to be one of those “highly paid Google engineers”. A Declarative Solution where we compose various functions to form a higher-order composite function that solves the problem, typically using java.util.stream.Stream or variants thereof. Creating smart applications powered by cognitive services such as machine learning, natural language processing, speech, vision, reasoning will require a look beyond today’s status quo of building imperative code in .NET or JavaScript. It’s not easy, but let’s just say a DSL is a clean, shiny layer on top of low-level constructs. Your database applications code will get much better. To go under the hood and change the tool, you need to learn about tokenizing and parsing, which is interesting and challenging, but hard. First, it defines a function, drawTable, to contain the presentation logic of drawing the product table. Readability/usability: a DSL is usually closer to a natural language (like English) than to pseudocode, hence more readable and also easier to learn by non-programmers. To the left is a flow-chart diagram trying to simulate an intelligent conversation for a fairly simple chatbot that can organize meetings for employees at Progress. In the example above we are defining several options for getting the specific doctor: In Angular 4 the data binding, template syntax, structural directives and pipes that you can use in your templates are one of the best examples of declarative syntax. Declarative languages like sql are not a dead end. To sum up; declarative templating tools suffer because: I would like to close the critique with an argument that is logically disconnected from the thread of this article, but deeply resonates with its emotional core: We have limited time to learn. There is literally an infinite number of example candidates that can be used for code metrics evaluation. In the end, we will also see how the learnings of this article can be applied in the field of database applications. Last month, I explained to Forbes how declarative programming helped us create a chatbot for a hospital 16 times faster and 2 cheaper than building it using imperative programming … (If you’ve ever written three nested callbacks in node.js, you know what I mean.). When relating all of this theory to your day-to-day work, there are several observations to make: While there are significant differences between CSS and JavaScript (and other imperative languages), I would definitely call both of them programming. Imagine that you need to write a web application with a non-trivial number of views. We have based our product on top of Wit.ai, since it has support for more than 55 languages, and has outstanding API. So the plumbing is a bit of a mess. Folks who work with XML a lot know about XSLT. The cognitive computing and AI definitely have the potential to change the way we develop software in the long-term. For instance, PHP is considered ‘lazy’ language, and JavaScript is ‘difficult predictable magic’. If it did, it wouldn’t be a DSL anymore, but rather a full programming language. One last question remains to be answered: What do I mean by walk, then slide? Read this article and understand how to become a better programmer using declarative code with functional composition. So, logical languages (like Prolog, miniKanren, etc.) The implementation details are abstracted away from us, but they are still there. In a nutshell, declarative programming consists of instructing a program on what needs to be done, instead of telling it how to do it. For HTML, these are the following: Believe it or not, these are the patterns you need to create an unfolding dsDSL layer that generates HTML. Let’s go back to our dsDSL for generating HTML. So, don’t run away from a worthy problem. But for more complex examples, reading the declarative code may not immediately make it apparent what the imperative rule is from which the code is derived. There's no hard line there. But they mostly are as they are. Both the inputs and the outputs of these functions can be contained and generated by a programming language without a separate syntax. Before we explore the limits of declarative programming, it is necessary to understand its merits. In a nutshell, declarative programming consists of instructing a program on what needs to be done, instead of telling it how to do it. In the case of SQL, the argument is weak because most of the things SQL offers are nothing like what you find in a normal programming language. Live Deep Fakes — you can now change your face to someone else’s in real time video applications. I think the general purpose vs special purpose/domain specific spectrum is much more relevant. Also declarative “code” is being more widely used to control cutting edge products like Docker and Kubernetes. You can write arbitrary code as long as that code returns a literal that conforms to a very specific, non-arbitrary form. But then perhaps this might counteract the benefits that you're talking about. The page shall be returned as an unmodifiable List of Person objects. In theory you can. At every step, each change (or differentiation, to use Alexander’s term) remains in harmony with any previous structure, when previous structure is, simply, a crystallized sequence of past changes. When we deal with a problem domain, we want to use a tool that delivers us from the nasty details of that domain. Brian Kernighan famously stated that, “Controlling complexity is the essence of computer programming.” If a tool adds significant complexity to your project, why even use it? Other notable declarative languages are regular expressions (which can be immensely useful for any computer user) and SQL (a database query language). If generate thoroughly validates its input (and it is both easy and important to thoroughly validate input, since these validation rules are the precise analog of a DSL’s syntax), it will tell you exactly where you went wrong with your input. Speedment Stream is a Stream-based Java ORM tool that can turn any database table/view/join into Java streams and thereby allows you to apply your declarative skills in database applications. Business logic certainly has no place in a template, but presentation logic exists nevertheless. Template systems are a perfect example. (It should be noted, though, that well-designed declarative languages can also avoid many common performance issues in imperative languages, so it goes both ways.). Cookies help us deliver our Services. The proliferation and success of startups focused on processing natural language in the form of voice and text was marked by key acquisitions. The thing I've realized about "declarative coding" is that it's actually not a separate type of coding. Regardless, it's definitely worthwhile for developers to be able to program effectively in both. While the above are all commonly cited advantages of declarative programming, I would like to condense them into two qualities, which will serve as guiding principles when I propose an alternative approach. And you have regular expressions. For example, the Collectors.toUnmodifiableList(), which would make our declarative Rest solution a bit shorter: Again, this will not impact the code metrics. If you are doing a standard project, a well-written standard tool should fit the bill.” Maybe yes, maybe no. Lowly programmers are becoming more like army generals who commands their forces by issuing orders which can be specific procedural: advance 5 mile to hill x or declarative: surround the enemy seventh corp with battalion ten. The humble HTML tag is a good example of patterns of representation. Indicates the complexity of the code and is a quantitative measure of the number of linearly independent paths through a program's source code. The best languages and tools rarely become popular because as an industry, programmers are more attuned to job protection than productivity. If the patterns of representation are the structures you use to express what you want, the patterns of generation are the structures your tool will use to convert patterns of representation into the lower level structures. Reuse: it is easier to create code that can be used for different purposes; something that’s notoriously hard when using imperative constructs. Some people think that some declarative languages are easily and commonly extended by the lowly programmer. And today, they are struggling to create text-based conversation.