Like most programming languages, Vimscript has functions. Let's take a look at how to create them, and then talk about some of their quirks.
Run the following command:
You might think this would start defining a function named
Unfortunately this is not the case, and we've already run into one of
Vimscript functions must start with a capital letter if they are unscoped!
Even if you do add a scope to a function (we'll talk about that later) you may as well capitalize the first letter of function names anyway. Most Vimscript coders seem to do it, so don't break the convention.
Okay, let's define a function for real this time. Run the following commands:
:function Meow() : echom "Meow!" :endfunction
This time Vim will happily define the function. Let's try running it:
Vim will display
Meow! as expected.
Let's try returning a value. Run the following commands:
:function GetMeow() : return "Meow String!" :endfunction
Now try it out by running this command:
Vim will call the function and give the result to
echom, which will display
We can already see that there are two different ways of calling functions in Vimscript.
When you want to call a function directly you use the
call command. Run the
:call Meow() :call GetMeow()
The first will display
Meow! but the second doesn't display anything. The
return value is thrown away when you use
call, so this is only useful when the
function has side effects.
The second way to call functions is in expressions. You don't need to use
call in this case, you can just name the function. Run the following command:
As we saw before, this calls
GetMeow and passes the return value to
Run the following command:
This will display two lines:
0. The first obviously comes from
echom inside of
Meow. The second shows us that if a Vimscript function
doesn't return a value, it implicitly returns
0. Let's use this to our
advantage. Run the following commands:
:function TextwidthIsTooWide() : if &l:textwidth ># 80 : return 1 : endif :endfunction
This function uses a lot of important concepts we've seen before:
If any of those sound unfamiliar you should go back a few chapters and read about them.
We've now defined a function that will tell us if the
textwidth setting is
"too wide" in the current buffer (because 80 characters is, of course, the
correct width for anything but HTML).
Let's try using it. Run the following commands:
:set textwidth=80 :if TextwidthIsTooWide() : echom "WARNING: Wide text!" :endif
What did we do here?
if's body wasn't executed.
Because we never explicitly returned a value, Vim returned
0 from the
function, which is falsy. Let's try changing that. Run the following commands:
:setlocal textwidth=100 :if TextwidthIsTooWide() : echom "WARNING: Wide text!" :endif
This time the
if statement in the function executes its body, returns
if we manually typed in executes its body.
:help :call. Ignore anything about "ranges" for now. How many arguments
can you pass to a function? Is this surprising?
Read the first paragraph of
:help E124 and find out what characters you're
allowed to use in function names. Are underscores okay? Dashes? Accented
characters? Unicode characters? If it's not clear from the documentation just
try them out and see.
:help return. What's the "short form" of that command (which I told you
to never use)? Is it what you expected? If not, why not?