Added multi-prompt format

Fix linter errors

FIx linter comment

Added backwards compatibility

chains/llm.go

@@ -19,6 +19,8 @@ type LLMChain struct {
 	Memory           schema.Memory
 	CallbacksHandler callbacks.Handler
 	OutputParser     schema.OutputParser[any]
+	// When enabled usesMultiplePrompts will not 'flatten' the prompt into a single message.
+	UseMultiPrompt bool
 
 	OutputKey string
 }
@@ -41,6 +43,7 @@ func NewLLMChain(llm llms.Model, prompt prompts.FormatPrompter, opts ...ChainCal
 		Memory:           memory.NewSimple(),
 		OutputKey:        _llmChainDefaultOutputKey,
 		CallbacksHandler: opt.CallbackHandler,
+		UseMultiPrompt:   false,
 	}
 
 	return chain
@@ -56,12 +59,17 @@ func (c LLMChain) Call(ctx context.Context, values map[string]any, options ...Ch
 		return nil, err
 	}
 
-	result, err := llms.GenerateFromSinglePrompt(ctx, c.LLM, promptValue.String(), getLLMCallOptions(options...)...)
+	var output string
+	if c.UseMultiPrompt {
+		output, err = llms.GenerateFromMultiPrompt(ctx, c.LLM, chatMessagesToLLmMessageContent(promptValue.Messages()), getLLMCallOptions(options...)...)
+	} else {
+		output, err = llms.GenerateFromSinglePrompt(ctx, c.LLM, promptValue.String(), getLLMCallOptions(options...)...)
+	}
 	if err != nil {
 		return nil, err
 	}
 
-	finalOutput, err := c.OutputParser.ParseWithPrompt(result, promptValue)
+	finalOutput, err := c.OutputParser.ParseWithPrompt(output, promptValue)
 	if err != nil {
 		return nil, err
 	}
@@ -87,3 +95,22 @@ func (c LLMChain) GetInputKeys() []string {
 func (c LLMChain) GetOutputKeys() []string {
 	return []string{c.OutputKey}
 }
+
+// Convert ChatMessage to MessageContent.
+// Each ChatMessage is directly converted to a MessageContent with the same content and type.
+func chatMessagesToLLmMessageContent(chatMessages []llms.ChatMessage) []llms.MessageContent {
+	msgs := make([]llms.MessageContent, len(chatMessages))
+	for idx, m := range chatMessages {
+		msgs[idx] = chatMessageToLLm(m)
+	}
+	return msgs
+}
+
+func chatMessageToLLm(in llms.ChatMessage) llms.MessageContent {
+	return llms.MessageContent{
+		Parts: []llms.ContentPart{
+			llms.TextContent{Text: in.GetContent()},
+		},
+		Role: in.GetType(),
+	}
+}

llms/llms.go

@@ -50,3 +50,20 @@ func GenerateFromSinglePrompt(ctx context.Context, llm Model, prompt string, opt
 	c1 := choices[0]
 	return c1.Content, nil
 }
+
+// GenerateFromMultiPrompt allows for calling an LLM with
+// a multiple prompts.
+func GenerateFromMultiPrompt(ctx context.Context, llm Model, msg []MessageContent, options ...CallOption) (string, error) {
+	resp, err := llm.GenerateContent(ctx, msg, options...)
+	if err != nil {
+		return "", err
+	}
+	choices := resp.Choices
+
+	if len(choices) < 1 {
+		return "", errors.New("empty response from model")
+	}
+
+	c1 := choices[0]
+	return c1.Content, nil
+}