SO: What's the motivation to use a phantom type?

### The question

Don Stewart's Haskell in the Large's presentation mentioned Phantom Types:

data Ratio n = Ratio Double
1.234 :: Ratio D3

data Ask ccy = Ask Double
Ask 1.5123 :: Ask GBP

What's the motivation to use a phantom type?

### The answer

To answer the "what's the motivation to use a phantom type". There is two points:

• to make invalid states inrepresentable
• carry some of the information on the type level

Read rest the rest on StackOverflow

• 2024-06-24 – hashable arch native
• 2024-05-28 – cabal fields
• 2024-04-21 – A note about coercions
• 2024-04-18 – What makes a good compiler warning?
• 2024-04-12 – Core Inspection

twitter github email linkedin stackoverflow