From 37f9cc184f0fff9d7b4c62aefc56fcecd2588d11 Mon Sep 17 00:00:00 2001
From: Yu Zhang <yu.zhang.yz862@yale.edu>
Date: Wed, 25 Dec 2024 19:03:31 +0800
Subject: [PATCH] add loop label

---
 next/language/fundamentals.md              | 11 +++++
 next/sources/language/src/controls/top.mbt | 48 +++++++++++++++++++++-
 2 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/next/language/fundamentals.md b/next/language/fundamentals.md
index d9741bfe..e13849c4 100644
--- a/next/language/fundamentals.md
+++ b/next/language/fundamentals.md
@@ -779,6 +779,17 @@ A functional loop consumes arguments and returns a value. It is defined using th
 Currently in `loop exprs { ... }`, `exprs` is nonempty list, while `for { ... }` is accepted for infinite loop.
 ```
 
+### Labelled Continue/Break
+
+When a loop is labelled, it can be referenced from a `break` or `continue` from
+within a nested loop. For example:
+
+```{literalinclude} /sources/language/src/controls/top.mbt
+:language: moonbit
+:start-after: start loop label
+:end-before: end loop label
+```
+
 ## Iterator
 
 An iterator is an object that traverse through a sequence while providing access
diff --git a/next/sources/language/src/controls/top.mbt b/next/sources/language/src/controls/top.mbt
index 768859cc..6b4cc9d5 100644
--- a/next/sources/language/src/controls/top.mbt
+++ b/next/sources/language/src/controls/top.mbt
@@ -1,3 +1,4 @@
+///|
 fn a() -> Int {
   let x = 1
   let y = 1
@@ -16,6 +17,7 @@ fn a() -> Int {
   // end conditional expressions 1
 }
 
+///|
 fn c() -> Unit {
   let size = 0
   // start conditional expressions 3
@@ -108,6 +110,7 @@ test "for loop 1" (t : @test.T) {
   t.snapshot!(filename="for_loop_1")
 }
 
+///|
 fn d() -> Unit {
   // start for loop 2
   for i = 0, j = 0; i + j < 100; i = i + 1, j = j + 1 {
@@ -116,6 +119,7 @@ fn d() -> Unit {
   // end for loop 2
 }
 
+///|
 fn infinite_loop() -> Unit {
   // start for loop 3
   for i = 1; ; i = i + 1 {
@@ -143,6 +147,7 @@ test "for loop 4" (t : @test.T) {
   t.snapshot!(filename="for_loop_4")
 }
 
+///|
 fn e() -> Unit {
   // start for loop 5
   for x in [1, 2, 3] {
@@ -211,7 +216,6 @@ test {
     i += j
   }
   assert_eq!(i, 45)
-
   let mut k = 0
   for l in 0..=10 {
     k += l
@@ -220,7 +224,42 @@ test {
 }
 // end for loop 10
 
+// start loop label
+test "break label" {
+  let mut count = 0
+  let xs = [1, 2, 3]
+  let ys = [4, 5, 6]
+  let res = outer~: for i in xs {
+    for j in ys {
+      count = count + i
+      break outer~ j
+    }
+  } else {
+    -1
+  }
+  assert_eq!(res, 4)
+  assert_eq!(count, 1)
+}
+
+test "continue label" {
+  let mut count = 0
+  let init = 10
+  let res =outer~: loop init {
+    0 => 42
+    i => {
+      for {
+        count = count + 1
+        continue outer~ i - 1
+      }
+    }
+  }
+  assert_eq!(res, 42)
+  assert_eq!(count, 10)
+}
+// end loop label
+
 // start guard 1
+///|
 fn guarded_get(array : Array[Int], index : Int) -> Int? {
   guard index >= 0 && index < array.length() else { None }
   Some(array[index])
@@ -231,17 +270,20 @@ test {
 }
 // end guard 1
 
+///|
 fn process(string : String) -> String {
   string
 }
 
 // start guard 2
+///|
 enum Resource {
   Folder(Array[String])
   PlainText(String)
   JsonConfig(Json)
 }
 
+///|
 fn getProcessedText(
   resources : Map[String, Resource],
   path : String
@@ -255,6 +297,7 @@ fn getProcessedText(
 }
 // end guard 2
 
+///|
 fn g() -> Unit {
   let condition = true
   let expr = Some(5)
@@ -266,6 +309,7 @@ fn g() -> Unit {
 }
 
 // start match 1
+///|
 fn decide_sport(weather : String, humidity : Int) -> String {
   match weather {
     "sunny" => "tennis"
@@ -277,4 +321,4 @@ fn decide_sport(weather : String, humidity : Int) -> String {
 test {
   assert_eq!(decide_sport("sunny", 0), "tennis")
 }
-// end match 1
\ No newline at end of file
+// end match 1