Underload Interpreter in Redcode

Underload is a stack-based esoteric programming language designed by ais523. A set of 8 single character instructions operate on a stack of variable length strings:

Ins	Description
:	copy the top stack entry
!	drop the top stack entry
~	swap the top two stack entries
*	join the top two stack entries
S	display then drop the top stack entry
^	drop then run the top stack entry
a	enclose the top stack entry in parentheses
( )	add a new stack entry

A combination of different factors make an interpreter for Underload an interesting project to tackle in Redcode:

• parsing single character instructions is easy, I don't like writing parsers
• handling variable length data can be tricky
• no operands / no side effects to worry about
• only 8 instructions, the size of the interpreter should be reasonable
• ^ is the only means of flow control

The final code weighs in at a mere 79 instructions. Here's the final version of the Underload Interpreter. If you have any improvements to suggest, please leave a comment below.