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version 0.1.0
TODO:
[WORKING] build MCTS() for planning
[] executeplan() to execute the plan
# YiemAgent
Change from version: 0.0.9
-
Julia framework for building agents with tool use and MCP (Model Context Protocol) support.
## Quick Start
```julia
using YiemAgent
# 1. Create an LLM callable (see "Custom LLM Callable" below)
llmCall = ...
# 2. Create a callable MCP server (see "MCP Server Integration" below)
mcpServer = ...
# 3. Create the agent
agent = yiemAgent(llmCall; mcpServer=mcpServer, eventSink=println)
# 4. Interact
promptAgent(agent, "What tools do you have?")
response = takeResponse(agent)
# 5. Stop when done
stopAgent(agent)
```
## Agent API
| Function | Description |
|----------|-------------|
| `promptAgent(agent, text)` | Send plain text to the agent's input channel |
| `promptAgent(agent, msg)` | Send a structured message (OpenAI format dict) to the input channel |
| `takeResponse(agent)` | Block and take the agent's response from output channel |
| `followUp(agent, text)` | Send plain text follow-up while agent is still processing |
| `followUp(agent, msg)` | Send a structured follow-up (OpenAI format dict) while agent is processing |
| `stopAgent(agent)` | Gracefully stop the agent and close channels |
## Creating a yiemAgent
```julia
yiemAgent(llmCall;
systemPrompt::String = "You are a helpful assistant.",
model = nothing,
messages::Vector{agentMessage} = agentMessage[],
prepareContext::Function = prepareContext,
formatMsgForLLM::Function = formatMsgForLLM,
beforeToolCall::Function = beforeToolCall,
afterToolCall::Function = afterToolCall,
sessionId::Union{String, Nothing} = nothing,
maxRetryDelayMs::Union{Int64, Nothing} = nothing,
parallelToolExecute::Bool = false,
eventSink::Function = eventSink,
mcpServer = nothing
)
```
| Parameter | Description |
|-----------|-------------|
| `llmCall` | **(required)** Function that receives formatted messages and returns an LLM response |
| `systemPrompt` | System prompt for the agent |
| `model` | LLM model configuration (`llmModel` struct) |
| `messages` | Initial conversation messages |
| `prepareContext` | Hook to transform messages/context before each LLM call |
| `formatMsgForLLM` | Hook to convert agent context to LLM API format |
| `beforeToolCall` | Hook to block/allow tool execution |
| `afterToolCall` | Hook to post-process tool results |
| `sessionId` | Optional session identifier for MCP server |
| `maxRetryDelayMs` | Maximum retry delay in milliseconds |
| `parallelToolExecute` | Run multiple tool calls in parallel |
| `eventSink` | Callback for agent events/debug messages |
| `mcpServer` | Callable struct for MCP server communication |
## Usage Examples
### Text Messages
```julia
# Send plain text
promptAgent(agent, "What tools do you have?")
response = takeResponse(agent)
# Follow-up while agent is processing
promptAgent(agent, "Tell me about wine")
followUp(agent, "Also include prices")
response = takeResponse(agent)
```
### Structured Messages (OpenAI Format)
```julia
promptAgent(agent, Dict("role" => "user", "content" => "Hello"))
response = takeResponse(agent)
```
### Output Format
`takeResponse()` returns a `Dict{String, Any}` in OpenAI message format:
```julia
Dict(
"role" => "assistant",
"content" => [
Dict("type" => "text", "text" => "The weather in Tokyo is Sunny, 22°C."),
# ... more content blocks
]
)
```
Content block types:
| Block Type | Fields | Description |
|------------|--------|-------------|
| `text` | `"type" => "text"`, `"text" => "..."` | Plain text response from the LLM |
| `image_url` | `"type" => "image_url"`, `"image_url" => Dict("url" => "...")` | Image content (rare, used by multimodal models) |
Example — extracting the text response:
```julia
response = takeResponse(agent)
text_response = first(c["text"] for c in response["content"] if c["type"] == "text")
```
### Multimodal Messages (Text + Image)
```julia
# Encode images to data URIs
image_path = "test/image.png"
image_bytes = read(image_path)
base64_string = base64encode(image_bytes)
data_uri = "data:image/png;base64,$(base64_string)"
# Build message with text and image content blocks
message = Dict(
"role" => "user",
"content" => [
Dict("type" => "text", "text" => "Do you have Brunello di Montalcino?"),
Dict("type" => "image_url", "image_url" => Dict("url" => data_uri))
]
)
promptAgent(agent, message)
response = takeResponse(agent)
```
### Custom Hooks
```julia
# beforeToolCall — request user approval for destructive tools
function my_before_tool_call(context::beforeToolCallContext, signal::abortSignal)::beforeToolCallResult
if context.toolCall.name == "deleteFile"
return beforeToolCallResult(true, "User must approve file deletion")
end
return beforeToolCallResult(false, "N/A")
end
# afterToolCall — mask sensitive data from results
function my_after_tool_call(context::afterToolCallContext, signal::abortSignal)::Union{agentToolResult, Nothing}
if context.isError
return agentToolResult(
[textContent("The tool encountered an error. Please try again.")],
context.result.details, context.result.usage, context.result.terminate
)
end
return nothing
end
agent = yiemAgent(llmCall;
mcpServer=mcpServer,
beforeToolCall=my_before_tool_call,
afterToolCall=my_after_tool_call,
eventSink=println
)
```
### Custom LLM Callable
```julia
function my_llm_call(messages_dict::Dict{String, Any})
# messages_dict contains "messages" key with OpenAI-format message array,
# plus optional "tools", "temperature", etc.
# Call your LLM provider (OpenAI, Anthropic, local model, etc.)
raw_response = call_my_llm_provider(messages_dict)
# Return a dict with these fields:
return Dict(
"message" => Dict("role" => "assistant", "content" => raw_response["content"]),
"finish_reason" => raw_response["finish_reason"],
"api" => "my_provider",
"provider" => "my_provider",
"model" => "my-model-name",
"usage" => llmUsage(100, 50)
)
end
```
### Custom Context Preparation
```julia
function my_prepare_context(state::agentState, eventSink)::agentContext
sysPrompt = state.systemPrompt * "\nCurrent time: $(now())"
msgs = deepcopy(state.messages)
# Prune old messages to fit context window
max_messages = 20
if length(msgs) > max_messages
msgs = msgs[end-max_messages+1:end]
end
return agentContext(sysPrompt, msgs, state.tools)
end
agent = yiemAgent(llmCall; prepareContext=my_prepare_context, ...)
```
## MCP Server Integration
YiemAgent uses JSON-RPC 2.0 for MCP communication. The `mcpServer` callable struct must implement `tools/list` and `tools/call` methods.
### Protocol
```julia
# tools/list — returns tool definitions
mcpServer("tools/list")
# → Dict("jsonrpc"=>"2.0", "id"=>1, "result"=>Dict("tools"=>[...], "nextCursor"=>...))
# tools/call — executes a tool
mcpServer("tools/call", toolName, arguments)
# → Dict("jsonrpc"=>"2.0", "id"=>2, "result"=>Dict("content"=>[...], "isError"=>...))
# Protocol error responses include "error" instead of "result":
Dict("jsonrpc"=>"2.0", "id"=>2, "error"=>Dict("code"=>-32602, "message"=>"..."))
```
### Example: NATS-based MCP Server Client
```julia
struct mcpServer
natsConn::NATS.Connection
topic::String
senderID::String
fileserver_url::String
end
# tools/list implementation
function (c::mcpServer)(method::String)
payload = Dict("jsonrpc" => "2.0", "id" => 1, "method" => method, "params" => Dict{String, Any}())
payloads = [("payload", payload, "dictionary")]
_, msg_envelope = msghandler.smartpack(c.topic, payloads;
sender_id=c.senderID, msg_purpose="mcp_tools_list", fileserver_url=c.fileserver_url)
reply = NATS.request(c.natsConn, c.topic, msg_envelope, timeout=180)
incoming = msghandler.smartunpack(String(reply.payload))
return incoming["payloads"][1][2]
end
# tools/call implementation
function (c::mcpServer)(method::String, toolName::String, arguments::Dict{String, Any})
payload = Dict("jsonrpc" => "2.0", "id" => 2, "method" => method,
"params" => Dict("name" => toolName, "arguments" => arguments))
payloads = [("payload", payload, "dictionary")]
_, msg_envelope = msghandler.smartpack(c.topic, payloads;
sender_id=c.senderID, msg_purpose="mcp_tool_call", fileserver_url=c.fileserver_url)
reply = NATS.request(c.natsConn, c.topic, msg_envelope, timeout=180)
incoming = msghandler.smartunpack(String(reply.payload))
return incoming["payloads"][1][2]
end
```
## Tool Discovery
Tools are discovered dynamically via the MCP server:
1. `listTools` is the only pre-registered tool at agent creation
2. When the LLM calls `listTools()`, tools are discovered from the MCP server and registered at runtime
3. Supports pagination via `nextCursor` for large tool sets
4. New tools become immediately available without restarting the agent
## Hooks
Hooks allow customization of the agent's behavior at key points in the execution pipeline.
| Hook | Signature | Purpose |
|------|-----------|---------|
| `prepareContext` | `(state::agentState, eventSink) -> agentContext` | Transform messages/context before LLM call (filter tools, inject context, prune messages) |
| `formatMsgForLLM` | `(ctx::agentContext, eventSink) -> Dict` | Convert agent context to LLM API message format |
| `beforeToolCall` | `(context::beforeToolCallContext, signal::abortSignal) -> beforeToolCallResult` | Block/allow tool execution; request user approval |
| `afterToolCall` | `(context::afterToolCallContext, signal::abortSignal) -> Union{agentToolResult, Nothing}` | Post-process tool results; mask sensitive data; set `terminate` flag |
| `eventSink` | `(msg) -> nothing` | Callback for agent events/debug messages throughout the pipeline |
## Agent Lifecycle
1. **Creation** — `yiemAgent()` spawns a background task (`_agentLoop`) listening on `inputChannel` and `followUpChannel`
2. **Input** — User messages enter via `promptAgent()` (immediate) or `followUp()` (queued while agent is busy)
3. **Processing** — `_processMessage()` handles LLM calls, tool execution, and conversation history in a loop
4. **Tool Execution Pipeline** — each tool call follows three phases:
- `prepareToolCall` — resolve tool, validate arguments, run `beforeToolCall` hook
- `executePreparedToolCall` — invoke `tool.execute()`
- `finalizeExecutedToolCall` — run `afterToolCall` hook, construct `toolResultMessage`
5. **Termination** — tool `execute` functions can set `terminate=true` to stop the agent loop
6. **Shutdown** — `stopAgent()` sends a `:shutdown` signal, drains channels, and closes the agent
## Architecture
```
src/
├── YiemAgent.jl # Module entry point
├── type.jl # Core types (messages, tools, agent state, events)
├── utils.jl # Message formatting, context preparation, validation
├── toolRegistry.jl # Tool store, MCP discovery, listTools registration
├── agentCore.jl # Agent loop, tool execution pipeline, yiemAgent struct
└── api.jl # Public API (promptAgent, takeResponse, followUp, stopAgent)
```