Domain-Specific Languages vs. Notation (spin.atomicobject.com)

Before you start throwing insults, what exactly is a language to you? I'm pretty confident that determining the difference between a language and an API is not so easy a thing to do.

A language has syntax and semantics; the combination of domain specific semantics with general purpose syntax is a domain-specific language.

Of course, with host languages that support user-defined syntax rules, an internal DSL may also have specialized syntax.

The cumbersome term you invented is not an accurate replacement for internal DSL.

I've seen the distinction between internal and external DSL in academia as well.

> it's pretty common for programmers to be undereducated...

[citation needed]

Usually you call something an internal DSL when it reads like its own language. The reason that Ruby lends itself to internal DSLs is how optional a lot of its punctuation is, especially parens around method parameters, making it easier to write code that looks like a variant of English. A good example of this is Rake.

I think the difference becomes clear when you consider that a language syntax is not just source code. Raw, text source code is just the means by which humans express utilizing the syntax of the language. Once that source code file is tokenized and parsed, it's no longer tied to whatever that text was. It becomes an abstract object in memory that either represents a process (a series of machine instructions) or is fed to a process to be manipulated and processed (i.e. interpreted scripting languages).

For example, this blog post walks through McCarthy's original specification for Scheme: http://programmingpraxis.com/2011/11/01/rip-john-mccarthy/

    apply[fn;x;a] =
         [atom[fn] → [eq[fn;CAR] → caar[x];
                     eq[fn;CDR] → cdar[x];
                     eq[fn;CONS] → cons[car[x];cadr[x]];
                     eq[fn;ATOM] → atom[car[x]];
                     eq[fn;EQ] → eq[car[x];cadr[x]];
                     T → apply[eval[fn;a];x;a]];
         eq[car[fn];LAMBDA] → eval[caddr[fn]; pairlis[cadr[fn];x;a]];
         eq[car[fn];LABEL] → apply[caddr[fn];x;cons[cons[cadr[fn];caddr[fn]];a]]]

This is a type of source code. Notice it even includes non-ASCII characters. But this code isn't executable as it is. It has to first be translated into a program, somehow. See the first reply at the original link, which I will not reproduce here, for brevity.

It is a Scheme interpreter. The call to `evaluate` at the end of each test function is where the program gets interpreted. No, it is not a Scheme source file, but it is Scheme syntax, written in Python.

Similarly, LINQ to SQL is a SQL syntax written in C#. Your LINQ expressions are C# code that construct objects that will be interpreted in a SQL context. LINQ to Objects, on the other hand, is NOT a SQL syntax, it's just a library. Even though the function calls look exactly the same, because the C# code you write defines objects that then execute in a C# context.

Of course, that's not to say most "DSL"s haven't misused the term "language". I see it applied a lot to interfaces of chainable method calls. It isn't a new language, it's an exploitation of the existing language. The code still executes in the host language's context, it does not define its own contexts or semantics in any way.

Look at Emscripten. Is it C because that was what the code was written as, or is it JavaScript because that is what the code gets translated to? It's C, because it creates an execution context within the JavaScript code to recreate C semantics.

Look at this toy language I once wrote (https://github.com/capnmidnight/betty-boop/blob/master/loosp...) and a Pong game that uses it (https://github.com/capnmidnight/betty-boop/blob/master/pong....). Is the Pong game Scheme because that's what it was written as, or is it JavaScript? It's JavaScript, because though the code looks like Scheme, it executes like JavaScript, it's just a different syntax that gets translated away.

shrug I just didn't like the attempt at language policing, because it seemed pointless. This, however, is a good question that I don't know the answer to.

The need to perform a platform-independent parse + compile is a large part of my personal concept of a DSL. This is not the same thing as writing shims and grafting new methods onto objects to mutate aspects of the language you're writing in already while tying yourself to, for example, variable scoping rules that is inherited from an implementor language. In fact, I've seen some people describe what amounts to a "Fluent API" as a DSL. Fluent APIs are great and help with usability of an API considerably, but I don't think of jQuery or Scalding as DSLs, just libraries that meet all the rules of their implementation languages. Perhaps some people simply don't care and just think of a DSL as a subset of a language regardless of implementation.

If I want to be a bit more specific, I think a DSL needs to be independent in syntax and semantics from any implementation environment or platform and that by leveraging the compiler of your implementation language that it limits the "language" aspect of the DSL. I believe most people are concerned about the "DS" aspect and in this respect that reduces a DSL to being just a higher-level API - an API is not necessarily Turing complete, after all, and while some APIs require some parsing to use, they are still.

An embedded language like how Lua is used oftentimes is not a DSL to me because it is general purpose and is perfectly fine to implement another DSL - a DSL to me should also imply that you can't use it to implement another arbitrary DSL. This will blur as what used to be DSLs add features that make them Turing complete (lots of crazy things possible with SQL and CSS these days).

I don't like to be a terminology Nazi or something, but I have no real rational explanation for why "DSL" in practice rubs me funny.

Not sure I understand the relevance. Especially when it is contrasted with API level thinking, which would hit this question equally oddly.

> It doesn't stack up well compared to FORTRAN or LISP, which were both its contemporaries, neither of which were actually really designed with readability in mind, whereas COBOL was.

I dunno that I'd say that without substantial qualifications. Much as I hate COBOL, and little as I've used either, from what I remember of each I'd probably still prefer COBOL to Fortran for a large business application, if those were the only two choices I had.

I wouldn't want to use COBOL over Fortran for scientific computing, and I prefer Lisp over either for most things.

> Further, everything I know that was designed to be "English-like", cut out the programmers, and let the business people program directly has been a total and utter failure, on that metric.

I would agree, though in many cases (SQL particularly is a strong example) that's often more a failure of the organizations using the technology than the technology itself.

It doesn't matter if you have business-side analysts that can use SQL if you by policy don't let anyone outside of the IT side of an organization have access and tools that allow the user to use SQL directly against the database.

The IT-as-high-priesthood cult in organizations is strong, and resistant to any application of technology that challenges the priesthood. And this is, IME, especially true in organizations where the IT organization (and particularly its leadership) isn't particularly technically strong to start with.