update repo layout

en/src/functional-programing/iterator.md

@@ -0,0 +1,21 @@
+# Iterator
+
+https://doc.rust-lang.org/stable/rust-by-example/flow_control/for.html#for-and-iterators
+
+```rust,editable
+// (all the type annotations are superfluous)
+// A reference to a string allocated in read only memory
+let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
+println!("Pangram: {}", pangram);
+
+// Iterate over words in reverse, no new string is allocated
+println!("Words in reverse");
+for word in pangram.split_whitespace().rev() {
+    println!("> {}", word);
+}
+
+// Copy chars into a vector, sort and remove duplicates
+let mut chars: Vec<char> = pangram.chars().collect();
+chars.sort();
+chars.dedup();
+```