Merge pull request #83 from fibonacci1729/profiles

WIT Syntax: `world`

Author: fibonacci1729

design/mvp/WIT.md

@@ -112,6 +112,9 @@ keyword ::= 'use'
           | 'tuple'
           | 'future'
           | 'stream'
+          | 'world'
+          | 'import'
+          | 'export'
 ```
 
 ## Top-level items
@@ -122,20 +125,32 @@ readability but this isn't required.
 
 Concretely, the structure of a `wit` document is:
 ```
-wit-document ::= interface-item*
+wit-document ::= (interface-item | world-item)*
 ```
 
-## Item: `interface`
+## Item: `world`
 
-Interfaces can be defined in a `wit` document. Interfaces have a name and a sequence of items and functions.
+Worlds define a [componenttype](https://github.com/WebAssembly/component-model/blob/main/design/mvp/Explainer.md#type-definitions) as a collection of imports and exports.
+
+Concretely, the structure of a world is:
 
 ```wit
-interface example {
-    thunk: func() -> ()
-    fibonacci: func(n: u32) -> u32
-}
+world-item ::= 'world' id '{' world-items* '}'
+
+world-items ::= export-item | import-item
+
+export-item ::= 'export' id ':' extern-type
+import-item ::= 'import' id ':' extern-type
+
+extern-type ::= ty | func-type | interface-type
+
+interface-type ::= 'interface' '{' interface-items* '}'
 ```
 
+## Item: `interface`
+
+Interfaces can be defined in a `wit` document. Interfaces have a name and a sequence of items and functions.
+
 Specifically interfaces have the structure:
 
 ```wit
@@ -151,7 +166,9 @@ interface-items ::= resource-item
                   | use-item
                   | func-item
 
-func-item ::= id ':' 'func' param-list '->' result-list
+func-item ::= id ':' func-type
+
+func-type ::= 'func' param-list '->' result-list
 
 param-list ::= '(' named-type-list ')'