Add functions example

Author: seanmccann

README.md

@@ -149,6 +149,65 @@ client.chat(
 # => "Anna is a young woman in her mid-twenties, with wavy chestnut hair that falls to her shoulders..."
 ```
 
+### Function Calling
+
+Developers can describe functions and have the model intelligently choose to output a JSON object containing arguments to call those functions.
+
+```ruby
+def get_current_weather(location:, unit: "fahrenheit")
+  # use a weather api to fetch weather
+end
+
+response =
+  client.chat(
+    parameters: {
+      model: "gpt-3.5-turbo-0613",
+      messages: [
+        {
+          "role": "user",
+          "content": "What is the weather like in San Francisco?",
+        },
+      ],
+      functions: [
+        {
+          name: "get_current_weather",
+          description: "Get the current weather in a given location",
+          parameters: {
+            type: :object,
+            properties: {
+              location: {
+                type: :string,
+                description: "The city and state, e.g. San Francisco, CA",
+              },
+              unit: {
+                type: "string",
+                enum: %w[celsius fahrenheit],
+              },
+            },
+            required: ["location"],
+          },
+        },
+      ],
+    },
+  )
+
+message = response.dig("choices", 0, "message")
+
+if message["role"] == "assistant" && message["function_call"]
+  function_name = message.dig("function_call", "name")
+  args =
+    JSON.parse(
+      message.dig("function_call", "arguments"),
+      { symbolize_names: true },
+    )
+
+  case function_name
+  when "get_current_weather"
+    get_current_weather(**args)
+  end
+end
+```
+
 ### Completions
 
 Hit the OpenAI API for a completion using other GPT-3 models: