Example session:
```
» 1 + 1
The Roc compiler had an internal error.
Please file a bug report at
https://github.com/roc-lang/roc/issues/new
Please include the following data:
Error message: intentional panic
Stack backtrace:
0: std::backtrace_rs::backtrace::libunwind::trace
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
1: std::backtrace_rs::backtrace::trace_unsynchronized
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
2: std::backtrace::Backtrace::create
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/backtrace.rs:331:13
3: panic_hook
at ./crates/repl_cli/src/lib.rs:52:41
4: call<fn(&core::panic::panic_info::PanicInfo), (&core::panic::panic_info::PanicInfo)>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/ops/function.rs:79:5
5: <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/alloc/src/boxed.rs:2029:9
6: std::panicking::rust_panic_with_hook
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:785:13
7: std::panicking::begin_panic_handler::{{closure}}
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:651:13
8: std::sys_common::backtrace::__rust_end_short_backtrace
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/sys_common/backtrace.rs:171:18
9: rust_begin_unwind
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:647:5
10: core::panicking::panic_fmt
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/panicking.rs:72:14
11: step
at ./crates/repl_ui/src/repl_state.rs:66:9
12: {closure#1}
at ./crates/repl_cli/src/lib.rs:109:21
13: call_once<roc_repl_cli::main::{closure_env#1}, ()>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/ops/function.rs:250:5
14: call_once<roc_repl_ui::repl_state::ReplAction, roc_repl_cli::main::{closure_env#1}>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/panic/unwind_safe.rs:272:9
15: do_call<core::panic::unwind_safe::AssertUnwindSafe<roc_repl_cli::main::{closure_env#1}>, roc_repl_ui::repl_state::ReplAction>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:554:40
16: ___rust_try
17: try<roc_repl_ui::repl_state::ReplAction, core::panic::unwind_safe::AssertUnwindSafe<roc_repl_cli::main::{closure_env#1}>>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:518:19
18: catch_unwind<core::panic::unwind_safe::AssertUnwindSafe<roc_repl_cli::main::{closure_env#1}>, roc_repl_ui::repl_state::ReplAction>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panic.rs:142:14
19: main
at ./crates/repl_cli/src/lib.rs:108:30
20: main
at ./crates/cli/src/main.rs:321:16
21: call_once<fn() -> core::result::Result<(), std::io::error::Error>, ()>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/ops/function.rs:250:5
22: __rust_begin_short_backtrace<fn() -> core::result::Result<(), std::io::error::Error>, core::result::Result<(), std::io::error::Error>>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/sys_common/backtrace.rs:155:18
23: {closure#0}<core::result::Result<(), std::io::error::Error>>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/rt.rs:166:18
24: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/core/src/ops/function.rs:284:13
25: std::panicking::try::do_call
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:554:40
26: std::panicking::try
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:518:19
27: std::panic::catch_unwind
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panic.rs:142:14
28: std::rt::lang_start_internal::{{closure}}
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/rt.rs:148:48
29: std::panicking::try::do_call
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:554:40
30: std::panicking::try
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panicking.rs:518:19
31: std::panic::catch_unwind
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/panic.rs:142:14
32: std::rt::lang_start_internal
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/rt.rs:148:20
33: lang_start<core::result::Result<(), std::io::error::Error>>
at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04/library/std/src/rt.rs:165:17
34: _main
Machine Target: MacArm64
```
left in perfcnt and criterion-perf-events because they are used in
nightly_benches, which is not included in the workspace so cargo doesn't
know about it. All the others are not currently used anywhere in the
repository.
This new flag determines whether we should introduce a new kind to
represent lambda sets, or whether lambdas should be erased. The latter
is not yet implemented.
