Error

Errors and exceptions in angle are tightly linked with the concept of optionally in variables:

The function parse string as int? either returns an int or a typed error "missing int" !int with associated (?todo) type format error or number to large etc

The result can be handled positively:
if result { print "we have a number %d" % result }
if no result { print "parse did not return a number" }
if result failed { print "we have an error %e" % result } or
if result failed { print "we have an error %s" % result.error }
on error { print "we have an error %e" % error }

Just like in swift optionals can be unwrapped with tailing ! which throws if the variables value is missing or erroneous.

Note that no result is true both for missing and erroneous objects, which might be sufficient for most control flow, otherwise one can distinguish with result == 0 == result null result missing result empty and result failed