ccmix is a simulator for the MIX computer written in fully constexpr C++. Finally there's a way to run MIX programs in your C++ compiler!
MIX programs written in ccmix look like this
machine m;
// Set initial values for registers
m.reg_a = word{0};
m.reg_i[0] = word{x};
m.reg_i[1] = word{y};
// The program
m.memory[0] = word{AXA, 0, 1, INC};
m.memory[1] = word{AXA, 0, 2, INC};
m.memory[2] = word{SPECIAL, 0, 0, HLT};
// Run, starting from memory location 0
m.run();
See more complete live example in Compiler Explorer.
Note that ccmix doesn't simulate MIX completely. Missing features include at least overflow toggle, I/O and some operators (shifts, move...).