Write plugin to be used in app

src/lib.rs

@@ -4,3 +4,15 @@ use extism_pdk::*;
 pub fn greet(name: String) -> FnResult<String> {
     Ok(format!("Hello, {}!", name))
 }
+
+#[plugin_fn]
+pub fn count_vowels(sentence: String) -> FnResult<String> {
+    let vowels = "aeiouAEIOU";
+    let mut vowel_count = 0;
+    for c in sentence.chars() {
+        if vowels.contains(c) {
+            vowel_count += 1;
+        }
+    }
+    Ok(format!("{vowel_count}"))
+}