A great question. Maybe everything should have been built on Scheme once . and . for . all But people and the world aren't like that. We are restless souls.
Getting a Lisp to run efficiently and effectively is more difficult than just writing an interpreter. I consider work on this problem to still be incomplete. For example, it should be possible to implement generic functions even more efficiently in Common Lisp implementations than is currently the case, in a way that preserves the ability to redefine the functions (and the classes they work with) dynamically. Robert Strandh has been working on general mechanisms supporting this and other improvements.
The answer is, "because somebody made it because they weren't happy with what already existed"
They also had Visual J# which ran on .NET, allowing Visual J++ and Java programs to target that platform.
(I think that the difference between Java and C# is similar to the difference between Common Lisp and Scheme.)
Dozens. The standard language has been through numerous revisions (C++ 2.0, 98, 03, 11, 14, 17, 23), with no doubt many more to come - each version is a dialect. And there have been dozens of compilers, all of which define extensions to the standard - some of those extensions are copied by other compilers (and may eventually end up in the standard), others are unique to that implementation - so each compiler (even each of its successive major releases) can be viewed as a dialect. And then there are dialects defined, not by the core language features, but by which features are used, by which external libraries are used, etc. One C++ programmer is addicted to esoteric template metaprogramming, another avoids templates and treats C++ as a slightly improved version of C. One C++ programmer uses every Boost library they possibly can, another refuses to use any third party dependencies. Aren’t those effectively different dialects, even if they are both using the exact same version of the same tools?
And then there are entire languages defined as extensions of C++, such as Apple’s Objective C++, or Microsoft’s Managed Extensions for C++ and then C++/CLI - and also more modest extensions such as OpenMP
Considering C++ is an object-oriented extension to C, it belongs alongside other such extensions - most notably Objective C and D, but there have been other attempts at that which weren’t successful - aren’t they all (in a sense) C dialects?
Why are there multiple dialects of real-world languages?
LISP is pretty minimal and simple. It's less of a language than a set of constructs for computation. Computers are made of abstractions on top of abstractions, so it makes sense for Lisp-based languages to evolve continuously. No one is better than the other, each target to their own niche. Just like other prog. languages, or real-world dialects.
The production-ready lisps are:
- Common Lisp: this one is standardized and the ecosystem is NOT fractured. Many implementations exist and work in parallel: SBCL, CCL, LispWorks, ECL, ABCL…
- Clojure (though there is also ABCL and I keep hearing good things about LispWork's Java interface)
- Schemes: some coming from university, with a fractured ecosystem.
Of course, nobody uses Arc for serious stuff (but we can have its syntax in CL and probably in Racket too).
(Lisp Flavored Erlang)
I remember in the 1980s someone remarked that C and Pascal were more similar than Maclisp and Interlisp.
Anyone who is interested in the design of prgramming languages will find it easy to make their own Lisp and try out any ideas that seem congenial to them. The natural and obvious consequence is a lot of Lisps.
Creatives gotta create.
Somehow, someone who makes a scripting language with C syntax , like Awk or Javascript, instinctively knows that it isn't C and not to call it that.
Because any time someone makes an (operator arg1 arg2 ...) language, they either put Lisp in the name, or else state elsewhere that it's a Lisp dialect.
Why does there need to be an endless progression of C-like dialects? They don't get called C, or rarely so.
The semantic differences between things called Lisp can be as large as between C++, Java, Javascript and Awk.
Many programming languages have been modeled on Algol; why are there so many Algols and why aren't they called that way? A lot of it is because of syntactic differences.
In the Lisp world, there are some mainstream languages that have the most users; if that's important to someone, they can stick with those and pretend the rest don't exist.
Isn't the point of Lisps to be endlessly customizable, making the invention of a new dialect less necessary?
The only Lisp I'd consider for a real project is probably Clojure and I'd even be hesitant about that. Sure, you can make a simple web project with Arc (HN), but it seems like you get 0 libraries, 0 interfaces with other systems and 0 tooling. Why would I bother with that?