Compound assignment is syntactic sugar to shorten expressions in which a binary operation (such as addition) uses a variable for the left-hand side, then assigns the result back to that variable.
More generally, it expands
a OP= b into
a = a OP b, where
OP is any supported binary operator.
All binary arithmetic and logic operators support compound assignment using a second set of operators.
Simply suffix the operation with
= like the following:
<$a = 10> <a *= 10> # desugars into: <a = <a> * 10> <a += 1> # desugars into: <a = <a> + 1> # etc...