Allow custom system prompt for Ollama functions (langchain-ai#3264)

docs/core_docs/docs/integrations/chat/ollama_functions.mdx

@@ -43,3 +43,13 @@ import OllamaFunctionsExtraction from "@examples/models/chat/ollama_functions/ex
 <CodeBlock language="typescript">{OllamaFunctionsExtraction}</CodeBlock>
 
 You can see a LangSmith trace of what this looks like here: https://smith.langchain.com/public/31457ea4-71ca-4e29-a1e0-aa80e6828883/r
+
+## Customization
+
+Behind the scenes, this uses Ollama's JSON mode to constrain output to JSON, then passes tools schemas as JSON schema into the prompt.
+
+Because different models have different strengths, it may be helpful to pass in your own system prompt. Here's an example:
+
+import OllamaFunctionsCustomPrompt from "@examples/models/chat/ollama_functions/custom_prompt.ts";
+
+<CodeBlock language="typescript">{OllamaFunctionsCustomPrompt}</CodeBlock>

examples/src/models/chat/ollama_functions/custom_prompt.ts

@@ -0,0 +1,64 @@
+import { OllamaFunctions } from "langchain/experimental/chat_models/ollama_functions";
+import { HumanMessage } from "langchain/schema";
+import { PromptTemplate } from "langchain/prompts";
+
+// Custom system prompt to format tools. You must encourage the model
+// to wrap output in a JSON object with "tool" and "tool_input" properties.
+const toolSystemPrompt =
+  PromptTemplate.fromTemplate(`You have access to the following tools:
+
+{tools}
+
+To use a tool, respond with a JSON object with the following structure:
+{{
+  "tool": <name of the called tool>,
+  "tool_input": <parameters for the tool matching the above JSON schema>
+}}`);
+
+const model = new OllamaFunctions({
+  temperature: 0.1,
+  model: "mistral",
+  toolSystemPrompt,
+}).bind({
+  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: ["celsius", "fahrenheit"] },
+        },
+        required: ["location"],
+      },
+    },
+  ],
+  // You can set the `function_call` arg to force the model to use a function
+  function_call: {
+    name: "get_current_weather",
+  },
+});
+
+const response = await model.invoke([
+  new HumanMessage({
+    content: "What's the weather in Boston?",
+  }),
+]);
+
+console.log(response);
+
+/*
+  AIMessage {
+    content: '',
+    additional_kwargs: {
+      function_call: {
+        name: 'get_current_weather',
+        arguments: '{"location":"Boston, MA","unit":"fahrenheit"}'
+      }
+    }
+  }
+*/

langchain/src/experimental/chat_models/ollama_functions.ts

@@ -93,7 +93,7 @@ export class OllamaFunctions extends BaseChatModel<ChatOllamaFunctionsCallOption
     } else if (functions.length === 0) {
       functions.push(this.defaultResponseFunction);
     }
-    const defaultContent = await TOOL_SYSTEM_PROMPT.format({
+    const defaultContent = await this.toolSystemPrompt.format({
       tools: JSON.stringify(functions, null, 2),
     });
     const systemMessage = new SystemMessage({ content: defaultContent });