ollama-haskell
Industry-grade Haskell client for Ollama local LLMs
https://github.com/tusharad/ollama-haskell
| LTS Haskell 24.65: | 0.2.1.0@rev:2 |
| Stackage Nightly 2026-10-26: | 0.4.2.0 |
| Latest on Hackage: | 0.4.2.0 |
Maintained by [email protected]
This version can be pinned in stack with:
ollama-haskell-0.4.2.0@sha256:b99db8b70752cad0f9a96dc3823d61b2a67e297ff4368b53986f7c343737b55b,7854Module documentation for 0.4.2.0
Depends on 21 packages(full list with versions):
Used by 2 packages in nightly-2026-10-26(full list with versions):
ollama-haskell
Modern Haskell client library for the Ollama local LLM engine.
Features
- Client-Centric Architecture: Thread-safe
OllamaClienthandle with connection pooling and resource management (newClient,defaultClient,clientFromEnv,withClient). - First-Class Streaming:
conduit-based response streaming (chatStream,generateStream,pullStream,pushStream,createModelStream). - Model Context Protocol (MCP) Bridge: Bidirectional integration with
mcp-serverfor converting between Ollama tools and MCP tools, running MCP servers via stdio or HTTP (Ollama.MCP). - Generic JSON Schema Derivation: Automatically derive JSON schemas from Haskell data types via
GHC.GenericswithToSchemaandformatFor. - Complete API Surface: Text generation, chat completions, vector embeddings, model management (list, show, copy, delete, pull, push, create), system endpoints, and System One decision evaluation.
- System One Decision Models: Native support for
/v1/systemonefast classification, binary probability (noul), and scoring (choiceQuestion,noulQuestion,scoreQuestion). - Structured Outputs DSL: Powerful
SchemaBuilderDSL (|+,|++,|!,|!!) for type-safe JSON Schema structured responses. - Function / Tool Calling: Full support for tool definitions (
Tool), tool calls (ToolCall), and execution results (toolResultMessage). - Thinking Models & Logprobs: Native support for reasoning models (
Think/ThinkingLevelwith custom model-defined levels) and token log probabilities (Logprob/TokenLogprob). - Environment & Auth Integration: Robust URL normalization for
OLLAMA_HOSTand bearer token support forOLLAMA_API_KEY. - Configurable Resilience: Flexible retry policies (
NoRetry,ConstantRetry,ExponentialRetry), custom timeouts, lifecycle callbacks, and structured logging. - Conversation Store: Transactional STM-backed
InMemoryStoreandConversationStoretypeclass for managing multi-turn chat sessions. - SDK Comparison Matrix: Detailed feature comparison against Python, JS/TS, and Go SDKs in COMPARISON.md.
Installation
Add ollama-haskell to your .cabal file:
build-depends:
base >= 4.17 && < 5
, ollama-haskell >= 0.4.2.0
Or using Stack in package.yaml:
dependencies:
- ollama-haskell >= 0.4.2.0
Quick Start (5 Lines)
import Data.List.NonEmpty (NonEmpty ((:|)))
import Data.Text.IO qualified as TIO
import Ollama
main :: IO ()
main = do
client <- defaultClient
res <- chat client $ chatRequest "qwen3.5:2b" (userMessage "Why is the sky blue?" :| [])
case res of
Left err -> print err
Right resp -> mapM_ (TIO.putStrLn . messageContent) (crMessage resp)
Streaming Responses with Conduit
Stream LLM responses token-by-token in real time:
import Conduit (mapM_C, runConduit, (.|))
import Control.Monad.IO.Class (liftIO)
import Data.List.NonEmpty (NonEmpty ((:|)))
import Data.Text.IO qualified as TIO
import Ollama
import System.IO (hFlush, stdout)
main :: IO ()
main = do
client <- defaultClient
let req = chatRequest "qwen3.5:2b" (userMessage "Count from 1 to 5." :| [])
-- Stream tokens to stdout as they arrive
runConduit $
chatStream client req .| mapM_C (\chunk -> liftIO $ do
mapM_ (TIO.putStr . messageContent) (crMessage chunk)
hFlush stdout
)
putStrLn ""
You can also accumulate all chunks at once with collectStream, or fold text with foldStream:
-- Collect all chunks:
chunks <- collectStream (chatStream client req)
-- Or fold into a single Text value:
fullText <- foldStream (\acc c -> acc <> maybe "" messageContent (crMessage c)) "" (chatStream client req)
Function & Tool Calling
Define function signatures with zero boilerplate using toolDef, objectParams, and typed parameters:
import Data.List.NonEmpty (NonEmpty ((:|)))
import qualified Data.Map.Strict as Map
import Ollama
calculatorTool :: Tool
calculatorTool =
toolDef "add" "Add two numbers" $
objectParams
[ ("a", numberParam (Just "First number"))
, ("b", numberParam (Just "Second number"))
]
["a", "b"]
main :: IO ()
main = do
client <- defaultClient
let req = (chatRequest "llama3.2:latest" (userMessage "What is 25 + 17?" :| []))
{ chatTools = Just [calculatorTool] }
res <- chat client req
case res of
Left err -> print err
Right resp -> case crMessage resp of
Just msg -> case messageToolCalls msg of
Just (call : _) -> do
putStrLn $ "Tool called: " <> show (tcfName (tcFunction call))
putStrLn $ "Arguments: " <> show (tcfArguments (tcFunction call))
_ -> putStrLn "No tool called."
Nothing -> putStrLn "No message returned."
Multimodal Vision
Load local images directly and send them to vision models (gemma3, qwen3.5:2b, etc.):
main :: IO ()
main = do
client <- defaultClient
img <- readImageBase64 "chart.png"
let msg = imageMessage "Describe the chart in 2 sentences." [img]
res <- chat client (chatRequest "gemma3:latest" (msg :| []))
case res of
Right resp -> mapM_ (putStrLn . messageFullText) (crMessage resp)
Left err -> print err
Thinking / Reasoning Models
Control chain-of-thought tokens on reasoning models (e.g. DeepSeek-R1, Qwen 3.5):
let req = (chatRequest "qwen3.5:2b" (userMessage "Which is larger: 9.11 or 9.9?" :| []))
{ chatThink = Just ThinkEnabled } -- or ThinkDisabled, ThinkLevel ThinkHigh, ThinkCustom "..."
res <- chat client req
case res of
Right resp -> case crMessage resp of
Just msg -> do
case messageThinking msg of
Just th -> putStrLn $ "Thinking trace:\n" <> th
Nothing -> pure ()
putStrLn $ "Answer:\n" <> messageContent msg
Nothing -> pure ()
Left err -> print err
System One Decision Models
Evaluate high-speed classification, probability (noul), and scoring with /v1/systemone:
let q1 = choiceQuestion "Customer eligibility" (Map.fromList [("eligible", Just "Standard"), ("ineligible", Nothing)])
q2 = noulQuestion "Will this cause churn?"
req = systemOneRequest "nimble" "Customer account history..." (Map.fromList [("q1", q1), ("q2", q2)])
res <- systemOne client req
Structured Outputs (JSON Schema DSL)
Enforce structured JSON output formats using SchemaBuilder (re-exported directly from Ollama):
import Data.Text.IO qualified as TIO
import Ollama
personSchema :: Schema
personSchema = buildSchema $ emptyObject
|+ ("name", JString)
|+ ("age", JInteger)
|! "name"
main :: IO ()
main = do
client <- defaultClient
let req = (generateRequest "qwen3.5:2b" "Generate a person profile.")
{ genFormat = Just (SchemaFormat personSchema) }
res <- generate client req
case res of
Left err -> print err
Right resp -> TIO.putStrLn (grResponse resp)
Environment Variables & Configuration
Construct a client using environment variables (OLLAMA_HOST, OLLAMA_API_KEY):
main :: IO ()
main = do
client <- clientFromEnv
-- Automatically connects to OLLAMA_HOST with optional Authorization: Bearer header
...
Or configure custom retry policies and loggers:
customConfig :: OllamaClientConfig
customConfig = defaultConfig
{ configBaseUrl = "http://my-ollama-server:11434"
, configTimeout = 120
, configRetry = ExponentialRetry 3 1000000 -- 3 retries with exponential backoff
, configLogger = Just (\level msg -> putStrLn $ "[" <> show level <> "] " <> show msg)
}
main :: IO ()
main = withClient customConfig $ \client -> do
...
Runnable Examples
The repository includes complete, tested runnable examples for every library feature:
| Target | Source File | Description |
|---|---|---|
ollama-example-basic-chat |
examples/BasicChat.hs |
Non-streaming chat, system messages, and throughput metrics. |
ollama-example-streaming-chat |
examples/StreamingChat.hs |
Conduit-based real-time response streaming. |
ollama-example-tool-calling |
examples/ToolCalling.hs |
Multi-turn tool execution loop with toolDef and objectParams. |
ollama-example-structured-output |
examples/StructuredOutput.hs |
Typed record JSON schema derivation via ToSchema and formatFor. |
ollama-example-embeddings |
examples/Embeddings.hs |
Modern batch embeddings (/api/embed) and legacy embeddings. |
ollama-example-model-management |
examples/ModelManagement.hs |
Version inspection, model listing, details, and active VRAM ps. |
ollama-example-generate |
examples/GenerateText.hs |
Single-turn text completion, streaming, and throughput metrics. |
ollama-example-vision |
examples/Vision.hs |
Multimodal chat and generation with local images (readImageBase64). |
ollama-example-logprobs |
examples/Logprobs.hs |
Token log probability inspection and alternative candidate analysis. |
ollama-example-thinking |
examples/Thinking.hs |
Reasoning models with ThinkDisabled, ThinkEnabled, and ThinkCustom. |
ollama-example-model-lifecycle |
examples/ModelLifecycle.hs |
Model copying, creation, blob checking, and deletion lifecycle. |
ollama-example-conversation-store |
examples/ConversationStore.hs |
STM-backed in-memory multi-turn conversation persistence. |
ollama-example-client-lifecycle |
examples/ClientLifecycle.hs |
clientFromEnv, withClient, retry backoff, and error taxonomy. |
ollama-example-mcp-bridge |
examples/MCPBridge.hs |
Bidirectional conversion between Ollama tools and MCP definitions. |
ollama-example-system-one |
examples/SystemOne.hs |
Specialized decision evaluation questions (/v1/systemone). |
ollama-example-mock-testing |
examples/MockTesting.hs |
Offline unit testing with withMockClient without a running server. |
ollama-example-all-features |
examples/AllFeatures.hs |
End-to-end showcase combining multiple library features. |
Run any example with Stack:
stack run ollama-example-tool-calling
Feature Matrix
| Feature | Haskell (ollama-haskell) |
Official Python (ollama-python) |
Official JS/TS (ollama-js) |
Community Go (ollama/ollama) |
|---|---|---|---|---|
| Strict Type Safety | ✅ Compile-time (PVP, Smart Constructors) | ⚠️ Type hints (Runtime) | ⚠️ TypeScript (Erased at runtime) | ✅ Go Structs |
| Response Streaming | ✅ conduit ($O(1)$ constant memory) |
⚠️ Python Generator | ⚠️ Async Iterator | ⚠️ Go Channels |
| Structured Output Derivation | ✅ GHC.Generics (ToSchema) |
⚠️ Pydantic BaseModel | ⚠️ Zod / JSON Schema | ⚠️ Manual JSON Schema |
| Model Context Protocol (MCP) | ✅ Native mcp-server Bridge |
❌ Manual | ❌ Manual | ❌ Manual |
| System One Decision Models | ✅ Full ADT (/v1/systemone) |
✅ Supported | ❌ None | ❌ None |
| Token Logprobs Support | ✅ Logprob / TokenLogprob |
✅ Supported | ❌ None | ❌ None |
| Thinking / Reasoning Models | ✅ Dedicated Think ADT |
⚠️ Dict parameters | ⚠️ Object properties | ⚠️ Raw parameters |
| Transactional Chat Store | ✅ STM InMemoryStore |
❌ None | ❌ None | ❌ None |
| Built-in Mock Testing | ✅ Ollama.Testing (Pure) |
❌ None | ❌ None | ❌ None |
| Configurable Retry & Backoff | ✅ Exponential & Constant ADT | ❌ Manual | ❌ Manual | ❌ Manual |
| Token Throughput Metrics | ✅ Native Calculation Helpers | ⚠️ Raw nanoseconds | ⚠️ Raw nanoseconds | ⚠️ Raw nanoseconds |
| Environment Auto-Discovery | ✅ clientFromEnv |
✅ Default client | ✅ Default client | ✅ Default client |
Documentation & References
- Comparison Deep Dive — Detailed architectural comparison across language ecosystems.
- CONTRIBUTING.md — Development setup, testing guidelines, and code style.
- CHANGELOG.md — Release notes and version changelog.
- Hackage Documentation — Full Haddock API reference.
License
MIT © 2024–2026 Tushar Adhatrao