Wish

Definition

A wish in Zef is a pure data structure that describes a side-effectful operation. It can be passed to the Zef runtime (specifically the FX system) with the intent/ wish to be executed. The FX system accepts the data structure and does the dirty work of interacting with the outside world. See Introduction to Zef-FX to learn more more about the managed effect system in Zef.

Naming across Ecosystems

Expressing effects to be performed as pure data structures that only describe what is to be done is a concept that is common across different languages and libraries.
We chose the name wish after we stumbled across it in Bret Vicotor's Realtalk, since the name was the least overloaded and expresses the fact that it is only an intent.

Naming in other ecosystems:

• Elm: "command"
• JS / Redux: "action"
• Scala / Zio: "effect"

Further Material and References

• Exotic Programming Ideas: Part 3 (Effect Systems) by Stephen Diehl
• Side Effects, Front and Center! by Pat Helland
• Effects as Data by Richard Feldman
• Magic Tricks with Functional Effects by John de Goes