docs: Add langchain_ollama example (#661)

packages/langchain_ollama/example/langchain_ollama_example.dart

@@ -0,0 +1,42 @@
+// ignore_for_file: avoid_print, unused_element
+import 'dart:io';
+
+import 'package:langchain/langchain.dart';
+import 'package:langchain_ollama/langchain_ollama.dart';
+
+void main() async {
+  // Uncomment the example you want to run:
+  await _example1();
+  // await _example2();
+}
+
+/// The most basic building block of LangChain is calling an LLM on some input.
+Future<void> _example1() async {
+  final llm = Ollama(
+    defaultOptions: const OllamaOptions(model: 'llama3.2'),
+  );
+  final LLMResult res = await llm.invoke(
+    PromptValue.string('Tell me a joke'),
+  );
+  print(res);
+  llm.close();
+}
+
+/// The most frequent use case is to create a chat-bot.
+/// This is the most basic one.
+Future<void> _example2() async {
+  final chatModel = ChatOllama(
+    defaultOptions: const ChatOllamaOptions(model: 'llama3.2'),
+  );
+
+  try {
+    while (true) {
+      stdout.write('> ');
+      final usrMsg = ChatMessage.humanText(stdin.readLineSync() ?? '');
+      final aiMsg = await chatModel([usrMsg]);
+      print(aiMsg.content);
+    }
+  } finally {
+    chatModel.close();
+  }
+}

packages/langchain_ollama/pubspec.yaml

@@ -29,4 +29,5 @@ dependencies:
   uuid: ^4.5.1
 
 dev_dependencies:
+  langchain: ^0.7.7+2
   test: ^1.25.8