Very good collection. To the standard type variables, I would add: i for an index s for state or stream Also, in the context of lens specifically, s,

Very good collection. To the standard type variables, I would add: i for an index s for state or stream Also, in the context of lens specifically, s, t, u for the nth "containing structure" in the type signature. There's a funny story Kmett told about exploring abstractions until he wound up with a type parameterized by i m a s t a b u and deciding he should probably call it quits when the code starts threatening him.