Why Vim is great (Exhibit 2: Vim is scriptable)

One great feature of Vim is that it is scriptable, which allows pretty much infinite customizability. I already blogged about a plugin I wrote for speeding up C++ coding, but there are many other far more useful plugins out there. The point is, if you're a programmer and you want to speed up something you're doing often, you can easily do it yourself if an appropriate plugin doesn't already exist or you can't find it. My example above is obviously covered by some excellent plugins, but they are much more heavyweight than what I wanted to do.

Another example where an existing script (probably) doesn't exist and that I encountered recently was reformatting some context free grammars encoded in LaTeX. I was helping organize all the exam problems from the last several years of our compiler design course into a problem book to give out to students for practice. There were probably more than 50 grammars in these problems, written in several different styles of marking nonterminals, listing rules etc. For example, these were three of the styles we had originally:

S \(\to\) aAbBa | bBaAb
A \(\to\) AaBb | Ba | a
B \(\to\) Ab | b

S \(\to\) A a A b
A \(\to\) A b
A \(\to\) d B
A \(\to\) f
B \(\to\) f

S \(\to\) AB | dC     A \(\to\) aCB | \(\varepsilon\) 
B \(\to\) eS | bC     C \(\to\) c | aB

We obviously wanted to have a uniform style for all these grammars, so I wrote a short script that reads in a grammar in any of the original styles and reformats it. Obviously, you could write a program in any language to do that, but since these grammars were part of a large document, you'd have to delimit them somehow for the external program or copy/paste them around. If you think about it, the problem was an exact fit for an editor because it is part of editing a document. Also, it's not really possible to do this with a macro that doesn't itself contain some code. In any case, writing the script took probably less than 20 minutes; far less than it would have taken me to manually convert all the grammars, not to mention far less error prone.

So how do you write these scripts? Vim has a buit-in scripting language (commonly referred to just as Vimscript) which is a dynamic language that feels sort of like Python, but has somewhat clunky syntax. I'm not going to talk about the language very much here because it's covered well elsewhere, for example in a series of IBM DeveloperWorks articles, and in Vim's help by typing :help script.

The other thing to note is that you can actually script Vim using several other (better) languages, namely Python, Ruby, Perl, Scheme and Tcl. You can find great info on these in Vim's help under python, ruby, perl, mzscheme and tcl, respectively. I've only tried the Python interface myself and found it more enjoyable than using Vimscript. However, there are some unfortunate caveats. First, you'll need Vim compiled with the appropriate flag set to enable each interface (for example +python or +python3). This in itself motivates people to write plugins in Vimscript since it is the only language guaranteed to be supported (I read somewhere that Python was supposedly included in all the binaries after Vim 7.0, but I haven't been able to verify that right now). Furthermore, debugging these external scripts is a lot harder as the error messages you get aren't very helpful.

In any case, scriptability is a great feature that opens up a lot of opportunities for increased productivity, and that's what we're all after :). Happy Vimming!