Add typed exceptions

[jonnyboyC]

Problem

So far we've only had a small subset of the functionality for exceptions. Currently we supports the syntax but not the behavior of typed and multiple arm exception handlers.

Solution

Built out the remaining functionality in order to implement exceptions. This includes

• New methods on the base Fiber class to handle the generation of an appropriate backTrace
• New instructions to implement the exceptions systems
• Update the compiler to emit instructions for each catch arms.

Below is an example.

try {
  try {
    raise Error("test");
  // check if raised error matches Runtime Error
  } catch e: RuntimeError {
    assert(false);
  // check if raised error matches Syntax Error
  } catch e: SyntaxError {
    assert(false);
  }
// check if raised error matches Error
} catch e: Error {
  assert(true)
}

Overall some of the goals with the design are to basically make both exception paths and non exception paths as fast as possible.

None Exception

• We take a small performance hit for having the fiber be larger
• We now typically have larger jumps as we have more instructions in place when handlers as present

Overall these both are still relatively cheap

• When we raise and don't catch we should exit basically immediately and print the trace
• For caught exceptions we do have to allocate a list of IPs which we use later to generate the backtrace

Overall we should be able to optimize this slightly as we have to do some double allocation at the moment.