Crosstwine Labs

From: redacted

I’m trying to study SKILL, but don’t know much about the language. I’ve only been writing small scripts so far—less that 2,000 lines.

Can you show me some larger examples of SKILL/SKILL++ code, and give me some goals to attempt?

Thanks, redacted

From: Damien Diederen <dd@crosstwine.com>
Date: Tue, 15 Jan 2013 11:59:12 +0100

Hello redacted,

SKILL++ is easy to get started with: just rename your script from <something>.il to <something>.ils!

If your code is simple enough, it is likely that it will still work and produce the same results as before. A big difference is that functions and variables are now in the same namespace, that is:

procedure(Foo(list)
  list(list)
)

println(Foo(42))

works in SKILL (.il file extension), but fails in SKILL++ (.ils), because of the confusion between list and… list.

In this case, Foo is better written as:

procedure(Foo(x)
  list(x)
)

which works in both dialects.

Try putting some of your code in .ils files (start small!), and tell me if something breaks that you cannot understand.

Note that even if these baby steps are not impressive, using .ils/SKILL++ is actually a huge improvement: it provides you access to modern language features. A very important one is lexical scoping; you can now use local helper functions!

let( ()
  procedure(Square(x)
    x*x
  ) ; procedure

  println(Square(2))
  println(Square(4))
) ; let

Note how the code above, while not terribly interesting, does what one would expect, and that the Square procedure is only visible within the let() block.

As to what is possible with SKILL++, the sky’s the limit! It’s a full-featured programming language; the only thing that is lacking is general-purpose libraries. I’ve started working on that; you can have a look at the source code of a lightweight CSV parser of mine:

http://crosstwine.com/veda/0.2.0/pkg/csv/csv.ils.html

Note that I’m using traditional Lisp syntax, but that’s not the point. One can perfectly write SKILL++ in infix notation.

Feel free to download my (growing) collection of SKILL/SKILL++ tools and libraries, and to use it for evaluation/learning purposes:

http://crosstwine.com/veda/

Note the version number, though: 0.2.0. It’s still very young; gotchas are to be expected. I’d be happy to have your feedback!

Cheers, -D