Function syntax::ext::tt::transcribe::transcribe

pub fn transcribe(
    cx: &ExtCtxt, 
    interp: Option<FxHashMap<Ident, Rc<NamedMatch>>>, 
    src: Vec<TokenTree>
) -> TokenStream

This can do Macro-By-Example transcription. On the other hand, if src contains no TokenTree::{Sequence, MetaVar, MetaVarDecl}s, interp can (and should) be None.