Function syntex_syntax::ext::deriving::generic::cs_fold

pub fn cs_fold<F>(use_foldl: bool, f: F, base: P<Expr>, enum_nonmatch_f: EnumNonMatchCollapsedFunc, cx: &mut ExtCtxt, trait_span: Span, substructure: &Substructure) -> P<Expr> where F: FnMut(&mut ExtCtxt, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>

Fold the fields. use_foldl controls whether this is done left-to-right (true) or right-to-left (false).