ocaml · ggsmith842 · Jun 26, 2024 · Jun 27, 2024 · Jun 27, 2024 · Jun 27, 2024
diff --git a/data/cookbook/extract-links-from-html/00-Re.ml b/data/cookbook/extract-links-from-html/00-Re.ml
@@ -0,0 +1,68 @@
+---
+packages:
+  - name: "re"
+    tested_version: "1.11.0"
+    used_libraries:
+      - re
+---
+
+(*
+
+Given an HTML document or string, we can use the `re` library to create a regular expression that finds the `href` tags containing web links.
+For example, in the sample below we would expect to find three links for this HTML document.
+
+Sample HTML: 
+
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>Sample HTML Page</title>
+</head>
+<body>
+    <header>
+        <h1>My Cool Learning Links</h1>
+    </header>
+    <main>
+        <section>
+            <H2>Click a link to get started!</H2>
+            <ul>
+                <li><a href="https://ocaml.org/docs">The Ocaml.org Learning Page</a></li>
+                <li><a href="https://pola.rs/">Pola.rs: Modern Python Dataframes</a></li>
+                <li><a href="https://www.nonexistentwebsite.com">It used to work.com</a></li>
+            </ul>
+        </section>
+    </main>
+</body>
+</html>
+
+`find_links` accepts an argument `html_content` of type string that contains our HTML content.
+
+Using `Re.Perl.re` create a Perl flavored regular expression that searches for the `a href` tags. You can view the pattern using  
+to understand more about what is going on. [Regex101](https://regex101.com/r/2Bs442/1)
+
+`Re.all` searches the entire `html_content` string for the `pattern`.
+
+We then pipe the output to `List.map`, since `Re.all` returns a list of all matches and applies the `Re.group.get` function to each group
+in the list. Passing `1` we get the substring versus the entire matching group. This way we only get the URL link and not the entire HTML tag.
+
+`List.iter` iterates through the `links` list and prints the URLs.
+
+*)
+let find_links html_content = 
+  let pattern = Re.compile (Re.Perl.re "<a[^>]* href=\"([^\"]*)") in
+  let links = Re.all pattern html_content 
+  |> List.map (fun group -> Re.Group.get group 1) in
+  List.iter print_endline links
+
+
+(*
+Example usage:
+First, define helper function `read_file` to read in HTML content at the path. Note: you may need to include `Open Stdlib` to access `In_channel`
+*)
+let read_file file = 
+  In_channel.with_open_text file In_channel.input_all
+
+
+(* Open the HTML file using `read_file` and find the links using the `find_links` function. *)
+let () = find_links (read_file "lib/webhtml/index.html")