013: Make Impossible States Impossible

The talks

• Make Impossible States Impossible from Elm Conf 2016
• Make Data Structures from Elm Europe 2018
• Elm Radio Episode 2: Intro to Opaque Types

Dealing with Impossible States

• Building up a "truth table" of possible states (see Evan's guide Types as Sets)
• Which rows are invalid?
• Create a new type with only the valid ones possible

More references

• elm-css

• Tereza's line-charts package

• Tereza's elm Europe talk

• elm-graphql

• Gilded rose live stream

• Snapshot testing (also called Approval Tests)

• Jeremy Fairbank's Boolean Blindness talk