Dissertation: Lazy Evaluation: From natural semantics to a machine-checked compiler transformation

In order to solve a long-standing problem with list fusion, a new compiler transformation, 'Call Arity' is developed and implemented in the Haskell compiler GHC. It is formally proven to not degrade program performance; the proof is machine-checked using the interactive theorem prover Isabelle. To that end, a formalization of Launchbury`s Natural Semantics for Lazy Evaluation is modelled in Isabelle, including a correctness and adequacy proof.