Update type hinting

Author: Sainan

docs/New Features/Type Hinting.md

@@ -2,19 +2,20 @@
 sidebar_position: 1
 ---
 Type-hinting looks like this:
-```pluto showLineNumbers
+```pluto
 local var: string = "hello world"
 ```
 It works with functions too:
-```pluto showLineNumbers
+```pluto
 local function myfunc(a: string, b: string): number
     return tonumber(a) + tonumber(b)
 end
 
 print(myfunc(1, "1")) -- This will emit a warning for argument type mismatch.
 ```
 There's no effect on performance. This is implemented entirely during the compilation phase.
-### What types can I use?
+
+### Primitive Types
 - `string`
 - `number`
   - `int`
@@ -24,15 +25,76 @@ There's no effect on performance. This is implemented entirely during the compil
 - `table`
 - `userdata`
 - `nil`
-- `void` (return type only)
 - `any`
 
+### Multiple Return Values
+
+For function return values, there is the `void` hint to indicate 0 return values, as well as the following syntax for 2 or more:
+
+```pluto
+local function get_status(): (bool, string)
+    return true, "OK!"
+end
+print(get_status())
+```
+
+### Union Types
+
 Prefix a `?` to indicate void-able types, e.g. `?string` indicates that it may be absent, nil, or a string.
 
 You can also use `|` to delimit alternatives, e.g. `string|int` indicates that it may be a string or an int.
 
 Putting all of this together, we could also have e.g. `?string|int` to indicate that it may be absent, nil, a string, or an int.
 
-:::info
-This is a WIP feature, and it's very difficult to implement in a one-pass compiler. Allow tolerance for missing coverage, and report any bugs.
-:::
+### Complex Table Types
+
+You can specify type requirements for fields inside of tables like so:
+
+```pluto
+local point: { x: number, y: number } = { x = 1, y = 2 }
+```
+
+### Named Types
+
+You can use `$type` to assign a name to a type.
+
+```pluto
+$type Point = { x: number, y: number }
+
+local p: Point = { x = 1, y = 2 }
+```
+
+### Complex Function Types
+
+You can also specify type expectations for the parameters and/or return values of functions.
+
+```pluto
+$type LogCallback = function(msg: string): void
+
+function write_env(log: LogCallback)
+    log(_VERSION)
+    log(_PVERSION)
+end
+
+write_env(print)
+```
+
+### `$declare`
+
+The parser can only do typechecking for what it can see, so `$declare` allows you to directly set the type of globals.
+
+```pluto
+$declare _VERSION: string
+```
+```pluto
+$declare function tonumber(str: string, base: ?number): number
+```
+
+### `$getproptype`
+
+If you want to know what type the parser propagation has detected for a given variable, you can use `$getproptype` to ask it:
+```pluto
+local x = "hello"
+print($getproptype(x)) --> string
+```
+Note that the return value of this function should not be relied upon.