Program two arms that loop forever and run in lockstep, assembling data records, then race to do it in fewer cycles.
Build instruction lists for two arms (A and B). Every cycle both arms execute one instruction and then loop. Read pulls feed values into bench slots, Grab takes one into the claw, Combine appends it to the record and Output emits a finished record. Meet the spec, then optimize.
Reactor Lines is a parallel-programming optimization puzzle about coordinating two concurrent loops without conflict.
Two arms each executing one instruction per cycle and then looping is the shape of a message-passing machine, and the same territory TIS-100 explores: concurrency without shared memory.
Reads pull values into bench slots, so the arms must agree about timing without being able to ask each other anything.
Getting that agreement by construction rather than by negotiation is what makes concurrent programming hard. Both arms are correct in isolation; the bug, when it comes, is that they are correct at the same moment.
Reactor Lines is a parallel-programming optimization puzzle about coordinating two concurrent loops. It is an original, free browser game built in-house for PlayPendium.