feat: Add intersperse()

Author: koraa

src/sequence.js

@@ -1439,6 +1439,29 @@ const zipLongest = curry('zipLongest', (seqs, fallback) => pipe(
  */
 const zipLongest2 = curry('zipLongest2', (a, b, fallback) => zipLongest([a, b], fallback));
 
+/**
+ * Inserts an element between every two elements of the given sequence.
+ *
+ * ```
+ * const { intersperse } = require('ferrum');
+ * assertSequenceEquals(
+ *   intersperse('ABC', '|'),
+ *   ['A', '|', 'B', '|', 'C']);
+ * ```
+ *
+ * @function
+ * @param {Any} what – The element to intersperse
+ * @param {Sequence} a
+ * @returns {Sequence}
+ */
+const intersperse = curry('intersperse', (seq, e) => pipe(
+  seq,
+  map(v => [e, v]),
+  flat,
+  trySkip(1)
+));
+
+
 /**
  * Forms a sliding window on the underlying iterator.
  *
@@ -1812,6 +1835,7 @@ module.exports = {
   zipLeast2,
   zip2,
   zipLongest2,
+  intersperse,
   slidingWindow,
   trySlidingWindow,
   lookahead,

test/sequence.test.js

@@ -26,7 +26,7 @@ const {
   take, takeWhile, takeUntilVal, takeDef, flat, concat, prepend, append,
   mapSort, zipLeast, zip, zipLongest, zipLeast2, zip2, zipLongest2,
   slidingWindow, trySlidingWindow, lookahead, mod, union, union2,
-  cartesian, cartesian2,
+  cartesian, cartesian2, intersperse,
 } = require('../src/index');
 const { ckEq, ckEqSeq, ckThrows } = require('./util');
 
@@ -525,3 +525,10 @@ it('union/union2', () => {
   ckEq(m2.get('b'), 99);
   ckEq(m2.get('x'), 13);
 });
+
+it('intersperse', () => {
+  ckEqSeq(intersperse('', 'x'), '');
+  ckEqSeq(intersperse('a', 'x'), 'a');
+  ckEqSeq(intersperse('ab', 'x'), 'axb');
+  ckEqSeq(intersperse('abc', 'x'), 'axbxc');
+});