Loyc.Syntax - how are classes (etc) represented?

[furesoft]

does a class node for example exists in loyc.syntax? its unusual to make an ast only for commands. i cant map properties events classes and so on?

[qwertie]

Loyc.Syntax implements Loyc trees, which only define literals, identifiers, calls and attributes. EC# is defined in terms of these concepts. For example class Foo {} is represented as a call to #class, specifically #class(Foo, #(), {}). (edit: corrected) Similarly, {} is represented as a call to '{}.

Using the Loyc.Ecs package you can construct one of these call nodes from text using ParseSingle, e.g.

var node = EcsLanguageService.Value.ParseSingle("public class Derived: Base {}");

There are methods in EcsValidators to deconstruct these nodes, but they are sometimes not intuitive to use. In the case of classes you can do

LNode name, baseList, body;
Symbol kind = EcsValidators.SpaceDefinitionKind(node, out name, out bases, out body);
if (kind == CodeSymbols.Class)
    Console.WriteLine("class {0} has these base types: {1}", name.Name, bases);
else
    Console.WriteLine("it wasn't a class");

It's called SpaceDefinitionKind because it detects any kind of "name space" - namespace, class, struct, interface, or enum.

If you're using LeMP/EC# it is easier to construct and detect these syntax trees using the quote and matchCode macros. Here is some EC# code that constructs and then deconstructs the same code:

LNode node = quote {
    public class Derived: Base {}
};
matchCode(node) {
    case { class $name: $(..baseList) { $(.._); } }:
        Console.WriteLine("class {0} has these base types: {1}",
            name.Name, String.Join(" ", baseList));
    default:
        Console.WriteLine("it wasn't a class");
}

Tips:

• $(..baseList) means to match a list of nodes, not just a single base
• The _ in $(.._); means "I don't care what's in here so don't create a variable to hold this information".
• The semicolon in $(.._); is important - the code won't work without it, but currently you don't get an error message when it is missing.

[qwertie]

It should be understood that Loyc trees themselves do not understand classes, functions, events, properties or anything else. Loyc trees are like XML: XML doesn't understand that <p>This</p> is a paragraph, because <p> is defined by HTML, not XML. In the same way, the LES code #fn(#int32, Five, #(), 5) represents the function int Five() => 5; in EC#, but LES doesn't know that. LES and Loyc trees don't have a concept of "functions" in the same way that XML doesn't have a concept of "paragraphs".