Operational Assignments

[faultyserver]

Operational assignments are common shorthands for "dual expressions", where an operation is performed, and then the result is re-assigned to the same left hand value used in the operation. For example:

a += 1
# is equivalent to
a = a + 1

For non-logical operations, this is essentially a simple syntax rewrite that takes any expression in the form a {{op}}= b and rewrites it as a = a {{op}} b. This works for all of the arithmetic and comparative operators.

However, ||= and &&= are generally handled differently, something that the semantics of which are surprisingly complex. I won't bother going into those semantics here, as it could easily take up multiple articles on its own.

In any case, the parser is already capable of parsing these statements, and has the corresponding OpAssign node to represent them. However, the interpreter does not actually support visiting these nodes, and will instead raise an error when encountered.

I would recommend a two-step approach to this, unless the second step becomes more simple.

1. Implement OpAssign for the arithmetic and comparative operators, but raise an UnsupportedError or similar when encountering ||= or &&=.

2. Go back and flesh out ||= and &&= properly once assignment methods are implemented (rewrites of obj.method = value to be equivalent to obj.method=(value), where method= is a method name.

[faultyserver]

This should be fully possible now that #24 has been implemented.