Support ? operator

[franziskuskiefer]

The question mark operator is not supported.

The following Rust code

fn inner() -> Result<(), u8> {
    Err(1)
}

fn call_it() -> Result<(), u8> {
    inner()?;
    Ok(())
}

generates the following C code.

core_result_Result_55 eurydice_tests_call_it(void)
{
  KRML_HOST_EPRINTF("KaRaMeL abort at %s:%d\n%s\n",
    __FILE__,
    __LINE__,
    "Eurydice error: Failure(\"TODO: TraitTypes core::result::{core::ops::try_trait::Try for core::result::Result<T, E>[TraitClause@0, TraitClause@1]}#26<T@0, T@1>[TraitClause@0, TraitClause@1]::Residual\")\n");
  KRML_HOST_EXIT(255U);
}

[msprotz]

This boils down to support for associated types, which would require a little bit of feature work, to encode the associated types in trait parameters as type arguments to pre-monomorphized functions.