polytropos-mcp

Model Context Protocol (MCP) JSON-RPC 2.0 server implementation for polytropos open records and variants.

Overview

polytropos-mcp implements the Anthropic Model Context Protocol specification for agentic tooling. It leverages open product rows for compile-time OpenAPI 3.0 tool schema generation and open variant sum rows for \(O(1)\) jump table tool call dispatch.

Features

• recordToTool: Derives compliant OpenAPI 3.0 input schemas directly from open product row types (Proxy (r :: Row)).
• toolCallToVariant & dispatchToolCall: Parses JSON tool call arguments into open variants and executes handlers via eliminateUniform.
• runStdioServer: Complete stdio server loop handling lifecycle handshakes (initialize, tools/list, tools/call).

Quick Example

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE OverloadedRecordDot #-}
{-# LANGUAGE TypeApplications #-}
{-# OPTIONS_GHC -fplugin=Polytropos.Plugin #-}

import Data.Proxy (Proxy (..))
import Data.Text (Text)
import Polytropos
import Polytropos.MCP

-- Define tool parameter rows
type SearchArgs = '["query" ':= Text, "limit" ':= Int]
type EchoArgs   = '["message" ':= Text]

-- Tool registry as an open variant
type MyTools = Variant
  '[ "search" ':= SearchArgs
   , "echo"   ':= EchoArgs
   ]

-- Export tool specifications with OpenAPI schemas
tools :: [McpTool]
tools =
  [ recordToTool @"search" "Search indexed documents" (Proxy @SearchArgs)
  , recordToTool @"echo"   "Echo back a message"      (Proxy @EchoArgs)
  ]

-- Dispatch calls in O(1) jump table
handleCall :: MyTools -> IO [McpContent]
handleCall = eliminateUniform REC
  { search = \args -> pure [TextContent ("Found hits for: " <> args.query)]
  , echo   = \args -> pure [TextContent ("Echo: " <> args.message)]
  }

License

Dual-licensed under EUPL-1.2 OR Apache-2.0.