SwiftModeStep2

Swift Mode Tutorial Step 2

Basic Language Features

Now that we have our basic Swift.seemode bundle in place, let's add some language specific highlighting.

Keywords and States

Let's have a look at the SyntaxDefinition.xml (for a complete Reference you can look in the Mode Documentation ).

The basic building blocks of a SyntaxDefinition are hierachical states and keywords living in that hierachical states. A state is something that has a defined begin and end, let's say for example a { } block. states are utilised for code folding and indenting.

keywords on the other hand are used for the actual highlighting. You can use simple strings like: if, else, class, import. For more complex constructs like number literals, or recognizing a function call you can also use regex to describe them. The scope attribute defines which type of keyword it is, and this scope is used in the .sss style sheet files to assign them a specific color.

The Keyword scopes

The scope="keyword.control" is meant to represent all basic control structure keywords. So let's lookup all of them in the Swift documentation and add the to the already existing keywords tag with the id="Control Flow Keyords".

<keywords id="Control Flow Keywords" scope="keyword.control" casesensitive="yes" useforautocomplete="yes">
	<string>for</string>
	<string>in</string>
	<string>do</string>
	<string>while</string>
	<string>if</string>
	<string>else</string>
	<string>switch</string>
	<string>case</string>
	…

After these we add additional keywords, which are not managing control flow with scope="keyword". In our default Style sheets the difference is visible so that keyword.control scoped keywords are shown bold, keywords are shown in normal weight. However, although the scope ulitmately is the deciding factor for the coloration, you should try and make the scope distinction a semantic one, not one that is based on how it is colored.

With the keywords in place, we already can see some progress in terms of highlighting:

States

Next up, let's add a state. A typical state is the comments. In Swift we have single and multiline comments almost the same way as in C - But there is a slight twist: multiline comments can now be nested. So to get a good head start, let us just grab the Comment state from the C mode, by finding and copying them into our top level default state. That is always something to keep in mind: if you know that a built-in mode already has a similiar feature, you can just look into the .seemode bundle and look up how it is done.

<state id="Comment" type="comment" scope="comment.block">
	<begin><regex>/\*</regex><autoend>\*/</autoend></begin>
	<end><regex>\*/</regex></end>
	<import mode="Base" state="EmailAndURLContainerState" keywords-only="yes"/>
</state>

<state id="SingleComment" type="comment" scope="comment.line">
	<begin><regex>//</regex></begin>
	<end><regex>[\n\r]</regex></end>
	<import mode="Base" state="EmailAndURLContainerState" keywords-only="yes"/>
</state>

So here we go. The begin and end tags enclose a regex tag which defines the begin and ends. We don't use special regex features here, but note that we needed to escape the * as it would otherwise be treated as a Regex modifier. Also of interest: we added the autoend to the multiline so the default shortcut option-command-. will insert a */ to close the current comment. This also needs to be escaped as it is a regular expression replace expression. You can have a look at the XML mode to see how to reference something from the begin in it.

The import tag imports the EmailAndURLContainerState from the base mode, which makes emails and urls clickable in comments. Also nice.

However, in the current form we don't support the correct way of highlighting the multiline comment in Swift. Swift allows nesting of /* */ comments and for us to enable it, we also need to nest the comment state in itself.

<state id="Comment" type="comment" scope="comment.block">
	<begin><regex>/\*</regex><autoend>\*/</autoend></begin>
	<end><regex>\*/</regex></end>
	<import mode="Base" state="EmailAndURLContainerState" keywords-only="yes"/>
	<state-link state="Comment" />
</state>

To achieve that we use the state-link tag. The state-link tag places the referenced state at this position. In contrast, the import tag places all the contents of the referenced state.

Also note that this state has the type="comment" attribute. You should always add this to comment states. There is a second variant - type="string" - which you also should use for all your String states. This can later be used by the SymbolParser to skip comment and string regions when recognizing items that should appear in the symbol popup in the top bar of SubEthaEdit.

Okay great. So now we have comments and basic keywords going on. Next up: Regex based keywords for numbers, functions and other neat things.

Step 1 - Getting Started - Overview - Step 3 - Regex based keywords