keel-onnx

Inference-only bindings to ONNX Runtime's C API, resolved entirely at run time: keel-dyn loads the official shared library, OrtGetApiBase() hands back the versioned function-pointer table, and every call goes through it. No build-time native dependency, no cbits in the shipped library.

import Keel.Onnx
import Data.ByteString qualified as BS

main :: IO ()
main = do
  Right ort <- loadOnnxRuntime
  model <- BS.readFile "model.onnx"
  withOrtEnv ort $ \env ->
    withSessionFromBytes env model $ \sess -> do
      [inName] <- inputNames sess
      [outName] <- outputNames sess
      out <- runFloats sess [(inName, [1, 4], xs)] [outName]
      print out

The runtime is located by the keel search policy (KEEL_ONNXRUNTIME env override, the per-user keel data dir — populated by keel setup onnx from the umbrella package — then the system search path). Absence of the runtime is an ordinary Left, never a crash.

The OrtApi slot indices are pinned against the vendored onnxruntime_c_api.h and verified by a test-suite-only C gate; the requested API version is the oldest whose frozen table prefix contains every slot used, so any ONNX Runtime release serves it. Inference results agree with Python onnxruntime to 1e-6 in the test suite, with a leak gate over 500 inference calls.

The vendored headers are Microsoft's, MIT-licensed — see LICENSE.onnxruntime.

Part of the keel workspace — see the project repository.