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output_parser.ts
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output_parser.ts
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import type { OpenAIClient } from "@langchain/openai";
import { AgentAction, AgentFinish } from "@langchain/core/agents";
import { BaseMessage, isBaseMessage } from "@langchain/core/messages";
import { ChatGeneration } from "@langchain/core/outputs";
import { OutputParserException } from "@langchain/core/output_parsers";
import { AgentActionOutputParser } from "../types.js";
/**
* Type that represents an agent action with an optional message log.
*/
export type FunctionsAgentAction = AgentAction & {
messageLog?: BaseMessage[];
};
/**
* @example
* ```typescript
*
* const prompt = ChatPromptTemplate.fromMessages([
* ["ai", "You are a helpful assistant"],
* ["human", "{input}"],
* new MessagesPlaceholder("agent_scratchpad"),
* ]);
*
* const modelWithFunctions = new ChatOpenAI({
* modelName: "gpt-4",
* temperature: 0,
* }).bind({
* functions: tools.map((tool) => convertToOpenAIFunction(tool)),
* });
*
* const runnableAgent = RunnableSequence.from([
* {
* input: (i) => i.input,
* agent_scratchpad: (i) => formatAgentSteps(i.steps),
* },
* prompt,
* modelWithFunctions,
* new OpenAIFunctionsAgentOutputParser(),
* ]);
*
* const result = await runnableAgent.invoke({
* input: "What is the weather in New York?",
* steps: agentSteps,
* });
*
* ```
*/
export class OpenAIFunctionsAgentOutputParser extends AgentActionOutputParser {
lc_namespace = ["langchain", "agents", "openai"];
static lc_name() {
return "OpenAIFunctionsAgentOutputParser";
}
async parse(text: string): Promise<AgentAction | AgentFinish> {
throw new Error(
`OpenAIFunctionsAgentOutputParser can only parse messages.\nPassed input: ${text}`
);
}
async parseResult(generations: ChatGeneration[]) {
if ("message" in generations[0] && isBaseMessage(generations[0].message)) {
return this.parseAIMessage(generations[0].message);
}
throw new Error(
"parseResult on OpenAIFunctionsAgentOutputParser only works on ChatGeneration output"
);
}
/**
* Parses the output message into a FunctionsAgentAction or AgentFinish
* object.
* @param message The BaseMessage to parse.
* @returns A FunctionsAgentAction or AgentFinish object.
*/
parseAIMessage(message: BaseMessage): FunctionsAgentAction | AgentFinish {
if (message.content && typeof message.content !== "string") {
throw new Error("This agent cannot parse non-string model responses.");
}
if (message.additional_kwargs.function_call) {
// eslint-disable-next-line prefer-destructuring
const function_call: OpenAIClient.Chat.ChatCompletionMessage.FunctionCall =
message.additional_kwargs.function_call;
try {
const toolInput = function_call.arguments
? JSON.parse(function_call.arguments)
: {};
return {
tool: function_call.name as string,
toolInput,
log: `Invoking "${function_call.name}" with ${
function_call.arguments ?? "{}"
}\n${message.content}`,
messageLog: [message],
};
} catch (error) {
throw new OutputParserException(
`Failed to parse function arguments from chat model response. Text: "${function_call.arguments}". ${error}`
);
}
} else {
return {
returnValues: { output: message.content },
log: message.content,
};
}
}
getFormatInstructions(): string {
throw new Error(
"getFormatInstructions not implemented inside OpenAIFunctionsAgentOutputParser."
);
}
}