{"ast_node_type":"struct","tokens":[{"end":68,"kind":"keyword","start":0,"text":"struct"}]}
    struct $Name: ident impl$( <$( $lifetime : lifetime ),+> )? Fn =
    {$( $( #[$attr: meta] )*
        |$( $arg: ident: $ArgTy: ty ),*| -> $ReturnTy: ty $body: block;