Merge pull request #8 from moonbitlang/hongbo/tweak_refine_todo

tweak & refine todo proposal

Author: bobzhang

proposals/0003-todo-cases.mbt.md

@@ -1,12 +1,13 @@
 # Support `...` in match cases
 
-* Proposal: [ME-0003](https://github.com/moonbitlang/moonbit-evolution/blob/0003-todo-cases/proposals/0003-todo-cases.mbt.md)
-* Author: [Yu-zh](https://github.com/Yu-zh)
-* Review and discussion: [Github issue](https://github.com/moonbitlang/moonbit-evolution/pull/4)
+- Proposal: [ME-0003](https://github.com/moonbitlang/moonbit-evolution/blob/0003-todo-cases/proposals/0003-todo-cases.mbt.md)
+- Author: [Yu-zh](https://github.com/Yu-zh)
+- Review and discussion: [GitHub issue](https://github.com/moonbitlang/moonbit-evolution/pull/4)
 
 ## Introduction
 
 In MoonBit, we can use `...` as a placeholder for unimplemented code. For example:
+
 ```moonbit
 fn init {
   fn unimplemented() {
@@ -22,22 +23,39 @@ further compiled. If `...` is reached at runtime, the program will panic.
 
 Currently, `...` is only allowed when a statement is expected. Therefore, if we
 want leave the code in match cases unimplemented, we have to write `_ => ...`:
+
 ```moonbit
-pub fn f1(x: Int) -> Unit {
+pub fn f1(x : Int) -> Unit {
   match x {
     0 => ()
-    _ => ...
+    ...
   }
 }
 ```
 
 We propose to extend the support to match cases so that we can write `...`
 directly:
+
 ```moonbit
-pub fn f2(x: Int) -> Unit {
+pub fn f2(x : Int) -> Unit {
   match x {
     0 => ()
     ...
   }
 }
-```
+```
+
+Note this means `...` can be used in any action case, including such cases:
+
+```moonbit
+pub fn f3() -> Unit {
+  ...
+  try {
+    ...
+  } catch {
+    ...
+  } noraise {
+    ...
+  }
+}
+```