Declarative programming : is a programming paradigm that expresses the logic of a computation(What do) without describing its control flow(How do). Well, F# has got you covered. Thanks for sharing! How so? You can love or hate declarative programming, but you cannot afford to ignore it. Let’s see the standard features of template systems and how they correlate to programming language facilities: This argument, that a DSL is limited because it simultaneously covets and rejects the power of a programming language, is directly proportional to the extent that the features of the DSL are directly mappable to the features of a programming language. Now, what are the merits of a dsDSL in contraposition to a DSL? m("body", [ "After examining hundreds of template files that I created over years of jGuru.com (and now in ANTLR v3) development, I found that I needed only the following four basic canonical operations (with some variations): Both the inputs and the outputs of these functions can be contained and generated by a programming language without a separate syntax. Imagine that SaveEmail invokes a SendEmail function that also accepts the string email. Or you can use JSX to create Mithiril: https://github.com/insin/msx That said, it is not necessarily unacceptable for a tool to be somewhat more complex than the lower level it intends to replace; if the tool yields code that is more readable, concise and correct, it can be worth it t. It’s an issue when the tool is several times more complex than the problem it replaces; this is flat-out unacceptable. Because the templating system uses a DSL, the syntax is different, so it cannot be in the same file. More sophisticated patterns, such as conditional iteration through an object to generate a table, may be implemented with functions that return the patterns of representation above, and these patterns map directly to HTML tags. To underline why these are excellent examples of unfolding, I would like to quote a few excerpts of a 1979 paper by Dennis Ritchie, one of the authors of Unix: “… the new process control scheme instantly rendered some very valuable features trivial to implement; for example detached processes (with &) and recursive use of the shell as a command. We will iterate printableFields and generate table headers for each of them: Notice that we have just implemented iteration, the workhorse of HTML generation, and we didn’t need any DSL constructs; we only needed a function to iterate a data structure and return dsDSLs. But what about the separation of concerns? The genius of the Unix pipeline is precisely that it is constructed from the very same commands used constantly in simplex fashion. The following code declares that intent without any unnecessary details: When we look beyond one simple example, we can see even more possibilities. I think IWML from ATOZED software complies more or less with this what youŕe describing, at first it will be a path to modernize DElphi Applications,and then will be disponibilized to any other framework,its a commercial product. The inner variable, printableFields, is the only place where you need to specify which fields are printable ones, avoiding repetition and inconsistencies in the face of changing requirements. So if we run generate (['a', {href: 'views'}, 'Index']), we will get the string Index. Please note that we’re not comparing the lower level solution against the best possible tool, but rather against no tool. could have the wrong initialization or the wrong increment, and if we’re inside a nested loop, we could accidentally mix up our variables. But both are more powerful than your dsDSL. To get in the mindset of thinking declaratively, we’ll start with a few overarching examples before diving into actual code. In other words, the complexity of the tool should remain constant, rather than growing with the amount of problems it solves. Thus, we guarantee that all entities passed parsing and we can rely on their data inside our domain. You are struggling to solve a straightforward problem that squarely belongs in the domain of the tool you are using, but the best Stack Overflow answer you find describes a, When this very straightforward problem could be solved by a certain feature (which does not exist in the tool) and you see a Github issue in the library that features a long discussion of said feature with. CAVEAT: This article emerged as the result of a multi-year personal struggle with declarative tools. Attributes are simply a list of key/value attributes, and contents may be either text or other tags. But of course functions have to be able to take more than one argument—so how does this work? By more complex, I mean more lines of code, code that’s harder to read, harder to modify and harder to maintain, but not necessarily all of these at the same time. By contrast, imperative programming focuses on the control flow and state changes of a program. We now turn to a second problem of declarative tools, which is widespread but not inherent. Although there are different types of template systems, we will sidestep their differences for the purpose of this analysis. A dsDSL has all the power of a programming language. I am exploring the possibilities of this approach for reactive programming and I hope to share it in the future. Business logic certainly has no place in a template, but presentation logic exists nevertheless. This is the dsDSL representation of the

we want to create. At first glance, they look kind of like enums on steroids, and they can carry custom information. And if you enjoy the paradigm and its tools, don’t take me too seriously. I found the language to be powerful and pleasant to use - coming from Javascript I could adapt to it with minimal difficulty. I open an exception for Embedded Ruby templates (ERB), because those are integrated into Ruby source code. React doesn't really use string interpolation as much as escapes to get you back to pure JavaScript, as I understand things. I think that it is, indeed, possible, as long as the language supports: I think this means that dsDSLs are tenable in any modern dynamic language (i.e. Having multiple levels make sense, as evidenced by the usefulness of assembler (a layer on top of object code), C (a layer on top of assembler) and dynamic languages ( (usually a layer on top of assembler or C). We want to overcome the separateness between the DSL and our programming language so that we are free to use the full power of a programming language whenever we need it. Because it is separate, a DSL needs to be located on a separate file; it is harder to modify (and even harder to write your own), and (often, but not always) needs you to add, one by one, the features you miss from a real programming language. I get why you've come down on the side of "it's still logic you need! A single tag with both attributes and contents: A group of tags (standalone or inside another tag): Depending on a condition, place a tag or no tag: Validate the input (this is actually is an universal pattern of generation). :), Programming is a very logical task and hence requires the developer to think about the logic behind the program. Note: There are other operators for functions in F#, but at their core they’re just different variations of the main ideas we’ve reviewed. We need a generate function which will take our dsDSL and yield a string with HTML. I just checked the StringTemplate, and I think you and I have the different understanding of Declarative Programming. Mithrill: I used it a few months ago and became very excited by the fact that it uses plain JS to create views! Its only purpose was to give us access to the current item in the collection. In more general terms, I would like to use expressions all the time, instead of a mixture of expressions and statements - and I feel that function applications written like this (the statements) cut the flow that you otherwise might achieve using 100% expressions. : Ruby, Python, Perl, PHP), but probably not in C or Java. I'll start with the moral of the story: programming is hard indeed!! Now, what the hell are patterns of representation and patterns of generation? An approach that worked well for me is to use arrays of strings to represent paths. I understand what you say and it's entirely tree that using arrays of strings is more verbose (for both reading and writing) than just using a string with a dot as a separator. In fact, lith does both, in ~250 lines of code. Many of its familiar features, like LINQ. In the case of value, I see that you use the dot (".") And not sure it's good to lose touch of what the machine is doing - all software ultimately is about memory and its manipulation, and thinking in those terms can allow insights that greatly simplify code/architecutre complexity.

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