Try/Catch

In Tele there is a typical convention of returning a tuple as a result to signify an error or not. This is a bit like the Result type in Rust.

For example some function foobar. Might return a result like this:

#('ok, v) = foobar()

OR

#('error, err) = foobar()

However, there are times when actual exceptions can happen. There are times when we might want to catch those exceptions for a variety of reasons. For that we use a try/catch expression. A try must be followed by a catch. An example might look like this:

try maybe_result():
  #('ok, _v) = foo: foo
catch:
  _._: #('error, 'oops)

Notice that the body of the try is pattern matching on the successful result of maybe_result. However we could match on other results:

try maybe_result():
  #('ok, 42): #('ok, 'right_number)
  #('ok, 43): #('ok, 'almost_right_number)
  _: #('error, 'undefined)

Here we are matching on an ok tuple that contains the number 42, or the number 43. If nothing matches we return an error tuple with the 'undefined atom. This works exactly like a case statement.

The catch expression works in a similar way except it matches on exceptions.

TODO: Describe exceptions in more detail