Add transformed

README.md

@@ -74,6 +74,7 @@ required and will default to an generic version of the parser.
 - `Parse.regex(regex: RegExp): (val: unknown) => string`
 - `Parse.literal(literal: unknown): (val: unknown) => literal`
 - `Parse.instanceOf<T>(classDef: Class): (val: unknown) => T`
+- `Parse.recordOf<K, V>(keyParser: Parser<K>, valParser: Parser<V>): (val: unknown) => Record<K, V>`
 
 ```ts
 // An array of strings
@@ -117,6 +118,26 @@ const numberOrNull = Parse.nullable(Parse.number);
 const optionalArrayOfStrings = Parse.optional(Parse.arrayOf(Parse.string)));
 ```
 
+Both `nullable` and `optional` can be passed `true` as a second parameter
+to allow parsing `null` or `undefined` into the respective empty value.
+
+For example, if you want to allow parsing a field that may be `null` or `undefined`,
+but want to return only `null` if either is parsed, you can use:
+
+```typescript
+const nullifiedVal = Parse.nullable(undefined, true); // parses to null
+```
+
+### Defaulting and Transforming
+
+Use `Parse.defaulted()` and `Parse.transformed()` to wrap parsers and provide
+a default value or value transformer
+
+```typescript
+const parsedWithDefault = Parse.defaulted(Parse.number, 42)(undefined); // 42
+const asNum = Parse.transformed(Parse.string, (val) => parseInt(val, 10))("42"); // 42
+```
+
 ### Extracting Types from Parsers
 
 When composing parsers to create more complex types, you can use the `ReturnType`