Developer Whitebeard tackled a quirky challenge: implementing Infocom’s 1980s Z-machine in Elm, a language built around immutable data and pure functions. The Z‑machine expects direct memory writes and a mutable stack, making Elm seem like the opposite of a natural fit. Still, the author pursued the experiment to see if Elm’s persistent structures could survive the low‑level demands.

Elm’s arrays rely on a RRB‑trie implementation, which allows efficient slicing and appending without copying the entire structure. Early tests confirmed acceptable speed, so the project progressed to full compliance. After weeks of parsing the Z‑machine spec—including a painful text‑encoding phase—the author produced a working emulator that loads .z3 files and passes the Czech compliance suite. It also supports snapshot save and restore.

The public API reduces interaction to a few pure functions: ZMachine.load converts a byte stream into a machine, ZMachine.runSteps executes a bounded instruction count, and step results enumerate output events such as PrintText or NeedInput. This design lets developers embed an interactive‑fiction player in browsers or Node apps with minimal glue code, demonstrating Elm’s surprising suitability for low‑level emulation.