#188: Made List.intersperse use heap, not stack

mperry · mperry · commit b95c232f78a9 · 2015-09-04T08:51:39.000+10:00
diff --git a/core/src/main/java/fj/data/List.java b/core/src/main/java/fj/data/List.java
@@ -1069,7 +1069,7 @@ public final Option<A> find(final F<A, Boolean> f) {
   public final List<A> intersperse(final A a) {
     return isEmpty() || tail().isEmpty() ?
            this :
-           cons(head(), cons(a, tail().intersperse(a)));
+            cons(head(), tail().bind(a2 -> List.list(a, a2)));
   }
 
   /**
diff --git a/core/src/test/java/fj/data/ListTest.java b/core/src/test/java/fj/data/ListTest.java
@@ -64,4 +64,12 @@ public void partition() {
         assertTrue(e.eq(p._2(), List.list(1, 3)));
     }
 
+    @Test
+    public void intersperseOverflow() {
+        // should not overflow
+        int n = 100000;
+        List<Integer> list = List.replicate(n, 1).intersperse(2);
+        String s = list.toString();
+    }
+
 }

Original file line number	Diff line number	Diff line change
`@@ -1069,7 +1069,7 @@ public final Option<A> find(final F<A, Boolean> f) {`
`1069`	`1069`	`public final List<A> intersperse(final A a) {`
`1070`	`1070`	`return isEmpty() \|\| tail().isEmpty() ?`
`1071`	`1071`	`this :`
`1072`		`- cons(head(), cons(a, tail().intersperse(a)));`
	`1072`	`+ cons(head(), tail().bind(a2 -> List.list(a, a2)));`
`1073`	`1073`	`}`
`1074`	`1074`
`1075`	`1075`	`/**`
Original file line number	Diff line number	Diff line change
`@@ -64,4 +64,12 @@ public void partition() {`
`64`	`64`	`assertTrue(e.eq(p._2(), List.list(1, 3)));`
`65`	`65`	`}`
`66`	`66`
	`67`	`+ @Test`
	`68`	`+ public void intersperseOverflow() {`
	`69`	`+ // should not overflow`
	`70`	`+ int n = 100000;`
	`71`	`+ List<Integer> list = List.replicate(n, 1).intersperse(2);`
	`72`	`+ String s = list.toString();`
	`73`	`+ }`
	`74`	`+`
`67`	`75`	`}`