AC_CHECK_LIB([expr], [_ZN3nix9EvalState17parseExprFromFileERKSs], [:],

AC_CHECK_LIB([expr], [_ZN3nix9EvalState8evalFileERKSsRNS_5ValueE], [:],

        [ "--with-nix=${nix}"

        [ "--with-nix=${nixUnstable}"

    Expr * e = state.parseExprFromFile(releaseExpr);

    state.mkThunk_(v, e);

    state.evalFile(releaseExpr, v);