Function map

map<T, O>(decoder: Decoder<T>, fn: (value: T) => O): Decoder<O>
Transforms the decoded value of a successful decoder.
Type Parameters
- T
- O
Parameters
- decoder: Decoder<T>
- fn: (value: T) => O
Returns Decoder<O>
Example
```
const date = map(string(), iso => new Date(iso));
```