created April 29, 2008 · complexity intermediate · author Clearmoments · version 7.0
Introduction
Since there isn't a lot of material on creating your own syntax files in Vim, I've decided to write a tutorial on the process. Currently, this tutorial only shows how to make Vim interpret the syntax of files by their file extension. Another tutorial may extend this to show how to interpret the syntax of files by their contents.
Example: Celestia star catalogs
For this tutorial I am creating a syntax file for Celestia star catalogs. Celestia is a great program for anyone who likes astronomy and space, but I digress. All we need to know for this tutorial is that a star catalog lists a star name along with its positional information, distance and attributes (color, radius, mass, brightness). An example entry in a star catalog file (.stc) can be:
600000 "My Star"
{
RA 24.406489
Dec -9.404052
SpectralType "Q"
Mass 1.09
AbsMag 1.29
Distance 124.729260
}
As you can see it consists of a number, a string, and a block ({...}), with some keywords within that block ("RA", "Dec", etc). Comments are marked out by a "#" like in shell scripts or conf files. In fact, the syntax looks a lot like a conf file. There can be multiple entries like this with a number (the HIP number), the string, and the block containing the attributes. Celestia gets more complicated than this because you can have multiple stars going around a barycenter, etc, but we are not going to get fancy. We'll cover only stars.
Syntax files
Get your directory straight
Syntax files are editor scripts, just like everything else, and are generally located in your personal $HOME/.vim/syntax directory. If that directory does not exist you can create it. There should also be a system-wide syntax file directory. It is preferable to use the personal syntax directory over the system-wide one since it is less likely to be overwritten by a newer Vim installation. A good reason to use the system-wide directory is if more than one user requires use of a syntax file. You can see these in Vim with the command:
:set rtp?
The system-wide syntax directory is going to be one of the entries separated with commas. The first value is normally your Vim personal syntax directory. You may want to study those syntax files and see how they are put together before playing around with it.
The system-wide and user syntax directories are OS and system dependent.
Unix
/usr/share/vim/vimxx/syntax
Where xx is the vim version. You can verify its location using the previous editor command, set :rtp?.
Windows
%PROGRAMFILES%\vim\vim71\syntax %PROGRAMFILES%\vim\vim71\cream\syntax
Under Windows you can create a $HOME environment variable manually. From Change the color scheme:
- On Windows, the $HOME environment variable can be set by going to your desktop, right click on "My Computer", click the "Advanced" tab, select "Environment Variables". If HOME is not in the list of variables, create a new variable named HOME and point it to the location of your vimrc.
Mac OS
For the terminal Vim it's the same as *nix:
/usr/share/vim/vimxx/syntax
If you're using the fantastic MacVim it's:
/Applications/MacVim.app/Contents/Resources/vim/runtime/syntax
(To get there, right click MacVim in the Applications directory and "Show Package Contents.") Keep in mind that they have separate system-wide directories, but will share the current personal directory at ~/.vim/
Build a syntax file
First, create a new file in Vim, and add the following contents:
" Vim syntax file
" Language: Celestia Star Catalogs
" Maintainer: Kevin Lauder
" Latest Revision: 26 April 2008
if exists("b:current_syntax")
finish
endif
Vim comments start with a quote. So I am following the convention of the built-in syntax files, and making a little comment flower box. The test if exists("b:current_syntax") ... checks whether an earlier file has defined a syntax already. If so, the script exits with finish.
Keyword, match and region elements
There are three major syntax elements, and commands to describe those elements. In order to syntax highlight, we must be able to describe what to highlight. Here is an example of what they look like:
" Keywords syn keyword syntaxElementKeyword keyword1 keyword2 nextgroup=syntaxElement2 " Matches syn match syntaxElementMatch 'regexp' contains=syntaxElement1 nextgroup=syntaxElement2 skipwhite " Regions syn region syntaxElementRegion start='x' end='y'
Keywords
Keywords are simple. Take for example the programming language BASIC. In BASIC there are several keywords like PRINT, OPEN and IF. Let's say you would like the editor to recognize them. You can define them like so:
syn keyword basicLanguageKeywords PRINT OPEN IF
For now we are not going to worry about nextgroup=.
The editor will now recognize the keywords PRINT, OPEN and IF as syntax elements of type basicLanguageKeywords. You can add more on the same line, or add another line with the same type (basicLanguageKeywords). In other words if I wanted to add the keywords DO, WHILE and WEND to my list, I could add to the previous line like this:
syn keyword basicLanguageKeywords PRINT OPEN IF DO WHILE WEND
Or, I could add another line, like this:
syn keyword basicLanguageKeywords PRINT OPEN IF syn keyword basicLanguageKeywords DO WHILE WEND
Let's use a more relevant example. Take our star catalog entry from above
600000 "My Star"
{
RA 24.406489
Dec -9.404052
SpectralType "Q"
Mass 1.09
AbsMag 1.29
Distance 124.729260
}
We can group the following keywords as part of a syntax element called celBlockCmd by adding the following to our syntax file.
syn keyword celBlockCmd RA Dec SpectralType Mass Distance AbsMag
The editor will now recognize them. Maybe that's enough for your purposes, but I wanted to make things a little more interesting with matches following the keywords, like those numbers and string values. How do we get those to be recognized?
Matches (and addendum to keywords)
All this keyword stuff logically leads to matches. Take the above example once again. After the keywords ("RA", "Dec", "AbsMag" etc) there are numbers. Let's say we want Vim to know that following a certain keyword there is going to be some set of characters to follow (defined as a regular expression maybe).
This is where matches come in; along with an additional caveat to using keywords, the nextgroup and skipwhite arguments as seen above.
syn match celNumber '\d\+' syn keyword celBlockCmd RA Dec Mass Distance AbsMag nextgroup=celNumber skipwhite
Now as you can see the match was given a regular expression \d\+ meaning to match one or more (\+) digits 0-9 (\d). The keyword syntax element celBlockCmd has been modified slightly because following the SpectralType keyword is not a number but a string. Hence it has been excluded from the list of keywords for now. Later in this article, we will address that problem by creating another regular expression to match strings and apply it to that keyword.
Notice the nextgroup argument. We are telling the editor to expect a celNumber after the keyword. So that's the first pattern the editor will attempt to match after finding one of those keywords.
The skipwhite argument simply tells the editor to expect some whitespace (tabs, spaces etc) between the keyword and the number.
You may have noticed a slight problem with my implementation. It will only match numbers like 19938, 93, and 0. It won't match decimals 3.91881 or negative numbers (-9).
How do we fix that? With more interesting regular expressions of course! This was taken from one of the existing Vim syntax files and modified slightly to work for our needs.
" Regular int like number with - + or nothing in front syn match celNumber '\d\+' syn match celNumber '[-+]\d\+' " Floating point number with decimal no E or e (+,-) syn match celNumber '\d\+\.\d*' syn match celNumber '[-+]\d\+\.\d*' " Floating point like number with E and no decimal point (+,-) syn match celNumber '[-+]\=\d[[:digit:]]*[eE][\-+]\=\d\+' syn match celNumber '\d[[:digit:]]*[eE][\-+]\=\d\+' " Floating point like number with E and decimal point (+,-) syn match celNumber '[-+]\=\d[[:digit:]]*\.\d*[eE][\-+]\=\d\+' syn match celNumber '\d[[:digit:]]*\.\d*[eE][\-+]\=\d\+'
Notice how we can keep creating more lines of syn match celNumber 'a pattern' to match all those patterns as one syntax element type (in this case celNumber.)
Regions
But we have another challenge that awaits us. Let's look at the star catalog entry again.
600000 "My Star"
{
RA 24.406489
Dec -9.404052
SpectralType "Q"
Mass 1.09
AbsMag 1.29
Distance 124.729260
}
The first number is outside of the brackets, and that's not really a number, that's an HIP catalog entry (more like a star's ID number rather than a value with physical meaning like mass or distance). The real numbers are the arguments to the keywords (like "RA" and "Dec"). It would be nice if we could have the editor match those differently than regular numbers. But, since celNumbers and HIPs consist of the digits 0-9 they conflict with one another. How can we fix that discrepancy?
Note that numbers with values exist only within brackets. Outside of the brackets it is an ID number rather than a value. We have to add another argument to the keyword and match definition blocks, and introduce another type of syntax element: a region.
First, we have to let the editor know that the aforementioned keywords only exist within brackets. Second, we specify that celNumber syntax elements only exist within brackets. This is the concept of a region.
syn region celDescBlock start="{" end="}" fold transparent
There we go, and we threw in some arguments for kicks. The fold argument means that Vim can increase the fold count inside brackets so you can press Ctrl+<F9> to expand and contract the code. The transparent is the important keyword here. It tells the editor to continue to apply matches and keywords to what's inside the region. Otherwise the region would not be colorized properly.
We must add another additional argument to finish off everything.
syn region celDescBlock start="{" end="}" fold transparent contains=celNumber,celBlockCmd
The contains argument tells the editor which syntax elements this region will contain. In this case keywords and numbers. But we have strings too, right? So let's implement the required syntax elements since we know all about keywords, matches and regions now. In addition we pickup another argument along the way, contained.
Let's define comments as a syntax element and see how contained works.
syn keyword celTodo contained TODO FIXME XXX NOTE syn match celComment "#.*$" contains=celTodo
Comments start with a "#" and run until the end of line. So that's a simple regular expression '#.*$'. Starts with a "#" and match all characters until the end of a line.
contained simply tells the editor that the keyword is only valid when contained by another syntax element, in this case a celTodo is only treated as a separate syntax element when contained by celComment.
So let's redefine everything from before, and implement all the required grammar, and bring this puppy together.
Bringing it together
syn keyword celTodo contained TODO FIXME XXX NOTE
syn match celComment "#.*$" contains=celTodo
"----------------------------------------------------------------
" Celestia Star Catalog Numbers
"----------------------------------------------------------------
" Regular int like number with - + or nothing in front
syn match celNumber '\d\+' contained display
syn match celNumber '[-+]\d\+' contained display
" Floating point number with decimal no E or e (+,-)
syn match celNumber '\d\+\.\d*' contained display
syn match celNumber '[-+]\d\+\.\d*' contained display
" Floating point like number with E and no decimal point (+,-)
syn match celNumber '[-+]\=\d[[:digit:]]*[eE][\-+]\=\d\+' contained display
syn match celNumber '\d[[:digit:]]*[eE][\-+]\=\d\+' contained display
" Floating point like number with E and decimal point (+,-)
syn match celNumber '[-+]\=\d[[:digit:]]*\.\d*[eE][\-+]\=\d\+' contained display
syn match celNumber '\d[[:digit:]]*\.\d*[eE][\-+]\=\d\+' contained display
syn region celString start='"' end='"' contained
syn region celDesc start='"' end='"'
syn match celHip '\d\{1,6}' nextgroup=celString
syn region celDescBlock start="{" end="}" fold transparent contains=ALLBUT,celHip,celDesc
syn keyword celBlockCmd RA Dec Distance AbsMag nextgroup=celNumber
syn keyword celBlockCmd SpectralType nextgroup=celString
Telling Vim how to highlight + final touches
You've reached the easiest part, just take the syntax element names you've used and use the hi def link command to tell Vim how to highlight.
Set the b:current_syntax variable to a name. I called it "cel". You'll need that name to modify the Un/Commentify (<F6>/Shift+<F6>) script in Cream for example to block comment-out lines with your new file types.
let b:current_syntax = "cel" hi def link celTodo Todo hi def link celComment Comment hi def link celBlockCmd Statement hi def link celHip Type hi def link celString Constant hi def link celDesc PreProc hi def link celNumber Constant
The hi def link command has different types of highlighting options that we needn't consider. The ones used here are:
- Todo: used for the todo comments (ones that have "TODO: blah blah" in them)
- Comment: indicates a code comment
- Statement: a code statement like a for loop or something
- Type: a user defined type generally
- PreProc: a pre-processor (like a C #include <stdio.h>)
- Constant: like a string or number in code
These of course are guidelines. For our purposes we really don't have statements or pre-processor commands, since this is really more like a conf file or like HTML. As you can see I set the celBlockCmds to use the Statement highlighting. As for the celHip I set that to a Type (seems like a close match to meaning).
You can view more options in Vim help: :help syntax
Save your work
Finally save your file as cel.vim (that's what I called it), in your Vim syntax directory (preferably your local one $HOME/.vim/syntax).
Setup your filetype.vim file
Okay, now we have to make sure Vim knows how to interpret your file. Add your filetype detection to filetype.vim, in this case your vim script is named cel.vim so you are going to use the filetype "cel".
au BufRead,BufNewFile *.stc setfiletype cel
See also
- Syntax folding of Vim scripts for an example of adding to an existing syntax instead of creating your own as this tip demonstrates.
- An actual stc syntax file: celstarcat.vim
- An actual ssc syntax file: celssc.vim
Comments
TO DO
- Check out that Windows $HOME stuff. The "proper" procedure for setting $HOME on Windows involves setting the home folder on the Profile tab of the user's properties in lusrmgr.msc (Windows 2000 or later). We need a tip on this; then just link to it.
- When I get a chance, I'll think about what to recommend for where syntax files should be placed. I suspect that the following statement is a little too dogmatic: "Syntax files ... are located in your personal $HOME/.vim/syntax directory".
Also mention using the $HOME/vimfiles/syntax (or $HOME/.vim/syntax) directory for syntax files that not everyone on the system will need. Less likely to be "blown away" by accident, and it won't need to be copied every version of Vim that comes out. --Fritzophrenic 13:15, 29 April 2008 (UTC)
You shouldn't add it in the $VIMRUNTIME syntax directory anyways, but in the $VIM/vimfiles/syntax directory for files that should be machine-shared and Vim-version-independent. --JeremyBarton 07:54, 30 September 2008 (UTC)