doc(context-fun): fix context-function literal

Author: robstoll

docs/docs/reference/contextual/context-functions.md

@@ -43,8 +43,17 @@ For example, continuing with the previous definitions,
 
   g(f(2))    // is expanded to g((using ev: ExecutionContext) => f(2)(using ev))
 
-  g((using ctx: ExecutionContext) => f(22)(using ctx)) // is left as it is
+  g(ExecutionContext ?=> f(22)) // is left as it is
 ```
+
+<!-- 
+
+TODO the previous proposed syntax does not compile:
+g((using ctx: ExecutionContext) => f(22)(using ctx)) // is left as it is
+results in `not a legal formal parameter`
+
+-->
+
 ### Example: Builder Pattern
 
 Context function types have considerable expressive power. For