I'm 
with @AliSoftware 's answer.
A type with prefix func / and postfix func / will conflict with /foobar/ regex syntax.
One extra note I want to add is that we might want to also consider about syntactic-level-macro like Rust has.
I won't push this macro idea further here in detail (because it's off topic), but when taking a look at its example:
let stylesheet: Stylesheet = css! {
.root {
width: 500px;
height: 120px;
flex-direction: row;
padding: 20px;
}
.image {
width: 80px;
margin-right: 20px;
}
.text {
height: 25px;
align-self: center;
flex-grow: 1;
}
};
let node: DOMNode = rsx! {
<view style={stylesheet.take(".root")}>
<image style={stylesheet.take(".image")} src="..." />
<text style={stylesheet.take(".text")}>
Hello world!
</text>
</view>
};
New DSL can be designed and written inside the macro scope.
This is almost analogous to #regex(...) being discussed so far, except that DSL design can be made by any developers (Rust) or compiler-internal only (Swift).
I'm OK with compiler-internal for now, but we could probably make them scalable to open syntactic-macro for any developers in future with minimal changes.