{"ast_node_type":"variable","tokens":[{"end":64,"kind":"keyword","start":0,"text":"let"}]}
                let fresh_var = self.next_ty_var(lhs_expr.span);
                let lhs_ty = self.check_expr(lhs_expr);
                self.demand_coerce(lhs_expr, lhs_ty, fresh_var, Some(rhs_expr), AllowTwoPhase::No)