Control Theory in Haskell

This module is the beginning of a set of data structures, algorithms, transfomers and adapters that implement concepts from control theory to modify the behavior of state machines and queues along the lines of proportional/integral/derivative controllers.

Some concepts:

• Feedback loops
• Rate-limiting
• Exponential back-off
• Introducing jitter
• Multi-point control systems
• Lag sensitivity (i.e., data freshness)
• Queue exhaustion
• Event vs. level triggering
• Flow control (using feedback to determine fair flow rates)
• Multi-variate controllers
• Hysteresis (history dependent behavior)

Example applications:

• Only spooling the same print job N times within X minutes

• Have 'make -j' be adaptive based on available memory and load average. This could be implemented by simply stopping (SIGSTP) and resuming child processes based on system feedback.

Data structures and algorithms:

• Queue adapters (also called moderators, governors)
• Age-based membership
• Retrying adapter with above behaviors (also called a mediator)
• Window-based triggers