Concrete implementations will perform their optimizations here
(peepholeOpt: StringAdd).self
(peepholeOpt: StringFormat).self
(peepholeOpt: ArrowAssoc[PeepholeOpt]).x
(Since version 2.10.0) Use leftOfArrow instead
(peepholeOpt: Ensuring[PeepholeOpt]).x
(Since version 2.10.0) Use resultOfEnsuring instead
Peephole optimization.