struct Expr {
    enum class Tag {
        Prim,
        Literal,
        Object,
        New,
        Array,
        Ref,
        VectorShortcut,
        Call,
        DotIndex,
        Subscript,
        Instance,
        Assign,
        BinOp,
        Conditional,
        UnOp,
        Closure,
        Seq
    } tag;
    srcspan_t span;

    Expr(Tag tag, srcspan_t span)
        : tag(tag)
        , span(span) {
    }
};
SYNTHESIZE_PM_BASE(ExprBase, Expr);

struct ExprPrim : public ExprBase<Expr::Tag::Prim> {
    enum class Kind {
        Undefined,
        True,
        False,
        Null,
        This,
        Super
    } kind;

    ExprPrim(srcspan_t span, Kind kind) :
        ExprBase(span),
        kind(kind) {
    }
};

struct ExprLiteral : public ExprBase<Expr::Tag::Literal> {
    enum class Kind {
        Decimal,
        Hexidecimal,
        String
    } kind;
    StringRef contents;

    ExprLiteral(srcspan_t span, Kind kind, StringRef contents) :
        ExprBase(span),
        kind(kind),
        contents(contents) {
    }
};