thread 'main' panicked at 'already borrowed: BorrowMutError', src/libcore/result.rs:1188:5
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:84
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1025
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1426
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:193
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:471
  11: rust_begin_unwind
             at src/libstd/panicking.rs:375
  12: core::panicking::panic_fmt
             at src/libcore/panicking.rs:84
  13: core::result::unwrap_failed
             at src/libcore/result.rs:1188
  14: core::result::Result<T,E>::expect
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/result.rs:983
  15: core::cell::RefCell<T>::borrow_mut
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/cell.rs:879
  16: gkquad::single::workspace::provider::WorkSpaceProvider::get_mut::{{closure}}
             at gkquad/src/single/workspace.rs:324
  17: std::thread::local::LocalKey<T>::try_with
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libstd/thread/local.rs:262
  18: std::thread::local::LocalKey<T>::with
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libstd/thread/local.rs:239
  19: gkquad::single::workspace::provider::WorkSpaceProvider::get_mut
             at ./src/single/workspace.rs:324
  20: <gkquad::single::algorithm::qags_finite::QAGS_FINITE as gkquad::single::algorithm::Algorithm<F>>::integrate
             at ./src/single/algorithm/qags_finite.rs:114
  21: <gkquad::single::algorithm::qags::QAGS as gkquad::single::algorithm::Algorithm<F>>::integrate
             at ./src/single/algorithm/qags.rs:37
  22: gkquad::single::integral::integral
             at ./src/single/integral.rs:18
  23: invalid::main::{{closure}}
             at gkquad/examples/invalid.rs:6
  24: <F as gkquad::single::common::Integrand>::apply
             at ./src/single/common.rs:135
  25: <gkquad::single::util::IntegrandWrapper<F> as gkquad::single::common::Integrand>::apply_to_slice::{{closure}}
             at ./src/single/util.rs:96
  26: core::iter::traits::iterator::Iterator::for_each::call::{{closure}}
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/iter/traits/iterator.rs:629
  27: core::iter::traits::iterator::Iterator::fold::ok::{{closure}}
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/iter/traits/iterator.rs:1829
  28: core::iter::traits::iterator::Iterator::try_fold
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/iter/traits/iterator.rs:1710
  29: core::iter::traits::iterator::Iterator::fold
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/iter/traits/iterator.rs:1832
  30: core::iter::traits::iterator::Iterator::for_each
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libcore/iter/traits/iterator.rs:632
  31: <gkquad::single::util::IntegrandWrapper<F> as gkquad::single::common::Integrand>::apply_to_slice
             at ./src/single/util.rs:96
  32: gkquad::single::qk_impl::imp::qk
             at ./src/single/qk_impl/naive.rs:62
  33: gkquad::single::qk::qk25
             at ./src/single/qk.rs:67
  34: <gkquad::single::algorithm::qags_finite::QAGS_FINITE as gkquad::single::algorithm::Algorithm<F>>::integrate
             at ./src/single/algorithm/qags_finite.rs:144
  35: <gkquad::single::algorithm::qags::QAGS as gkquad::single::algorithm::Algorithm<F>>::integrate
             at ./src/single/algorithm/qags.rs:37
  36: gkquad::single::integral::integral
             at ./src/single/integral.rs:18
  37: invalid::main
             at gkquad/examples/invalid.rs:4
  38: std::rt::lang_start::{{closure}}
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libstd/rt.rs:67
  39: std::rt::lang_start_internal::{{closure}}
             at src/libstd/rt.rs:52
  40: std::panicking::try::do_call
             at src/libstd/panicking.rs:292
  41: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:78
  42: std::panicking::try
             at src/libstd/panicking.rs:270
  43: std::panic::catch_unwind
             at src/libstd/panic.rs:394
  44: std::rt::lang_start_internal
             at src/libstd/rt.rs:51
  45: std::rt::lang_start
             at /rustc/eb3f7c2d3aec576f47eba854cfbd3c1187b8a2a0/src/libstd/rt.rs:67
  46: main
  47: __libc_start_main
  48: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.