Add intersperse() method for arrays (#1897)

crates/typst/src/eval/array.rs

@@ -287,6 +287,30 @@ impl Array {
         Ok(result)
     }
 
+    /// Returns an array with a copy of the separator value placed between
+    /// adjacent elements.
+    pub fn intersperse(&self, sep: Value) -> Array {
+        // TODO: Use https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.intersperse
+        // once it is stabilized.
+        let size = match self.len() {
+            0 => return Array::new(),
+            n => (2 * n) - 1,
+        };
+        let mut vec = EcoVec::with_capacity(size);
+        let mut iter = self.iter().cloned();
+
+        if let Some(first) = iter.next() {
+            vec.push(first);
+        }
+
+        for value in iter {
+            vec.push(sep.clone());
+            vec.push(value);
+        }
+
+        Array(vec)
+    }
+
     /// Zips the array with another array. If the two arrays are of unequal length, it will only
     /// zip up until the last element of the smaller array and the remaining elements will be
     /// ignored. The return value is an array where each element is yet another array of size 2.

crates/typst/src/eval/methods.rs

@@ -154,6 +154,7 @@ pub fn call(
                 let last = args.named("last")?;
                 array.join(sep, last).at(span)?
             }
+            "intersperse" => array.intersperse(args.expect("separator")?).into_value(),
             "sorted" => array.sorted(vm, span, args.named("key")?)?.into_value(),
             "zip" => array.zip(args.expect("other")?).into_value(),
             "enumerate" => array

docs/reference/types.md

@@ -1029,6 +1029,12 @@ Combine all items in the array into one.
   An alternative separator between the last two items
 - returns: any
 
+### intersperse()
+Returns a new array with a separator placed between adjacent items.
+
+- separator: any (positional)
+  The value to insert between each item of the array.
+
 ### sorted()
 Return a new array with the same items, but sorted.
 

tests/typ/compiler/array.typ

@@ -216,6 +216,13 @@
 // Ref: true
 #([One], [Two], [Three]).join([, ], last: [ and ]).
 
+---
+// Test the `intersperse` method
+#test(().intersperse("a"), ())
+#test((1,).intersperse("a"), (1,))
+#test((1, 2).intersperse("a"), (1, "a", 2))
+#test((1, 2, "b").intersperse("a"), (1, "a", 2, "a", "b"))
+
 ---
 // Test the `sorted` method.
 #test(().sorted(), ())