Parsing (Validation) done right for Elm

... in my mind, the difference between validation and parsing
lies almost entirely in how information is preserved.

Basic types

Lets look at the Parser type and dissect it:

type alias Parser inp err out =
    inp -> Result (Cons err) out

Type parameter	Meaning	Example
`inp`	Input type (what is parsed/validated)	User input typically its a `String`
`err`	Error type	Could be your custom error type `type Error = Empty
`out`	Output type	Could be your domain type `type Email = Email String`

Graphically:

 inp ────────┬──────── ▶ Ok out
             │
             ▼
      Err (Cons err)

(Cons is a non-empty list from this library)

Take a look at this examples: