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Evaluation

Tools for simulating HAL expressions before publishing. Expressions run in a sandboxed Tevm fork — no real transactions are submitted.

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Evaluate Existing Action

Simulate a saved action by ID. Loads the action’s HAL expression, injects the main() call with provided inputs, and simulates the entire action.

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Parameters

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Returns

  • Evaluation result — Final output of the expression
  • Operation log (oplog) — Full trace of every function call during execution
  • Simulated transaction hashes — Can be inspected with Query Transaction
Always simulate actions before publishing. Iteration is expected: simulate → inspect results with Query Transaction (works on simulated tx hashes) → fix issues → simulate again.

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Evaluate Arbitrary Expression

Evaluate a complete, self-contained HAL expression in a sandboxed Tevm fork. Use this for testing expressions that aren’t saved yet.

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Parameters

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Returns

  • Evaluation result — Final output
  • Operation log (oplog) — Full execution trace
Before constructing a HAL expression, read the HAL documentation using the Documentation tool with document IDs hal://spec/syntax, hal://spec/modules/herd, and hal://spec/examples. HAL has non-obvious syntax requirements (e.g., ABI arrays must be wrapped in ["quote", [...]] to prevent evaluation).

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Tevm Fork Behavior

  • Forks are created lazily — only when the expression performs on-chain actions (read-function, write-function, swap)
  • Pure expressions evaluate without any blockchain interaction
  • Simulated transaction hashes can be queried with Query Transaction to inspect traces

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Understanding Oplogs

Both evaluation tools return an operation log (oplog) — a detailed trace of every function call during execution. Each entry contains:

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Debugging with Oplogs

  • Trace execution flow — See which functions run and in what order
  • Inspect inputs/outputs — Check what each function receives and returns
  • Identify failures — Failed operations show "status": "error" with error messages
  • Inspect transactions — Use simulated tx hashes with Query Transaction to discover missing approvals, encoding errors, etc.

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Simulation Workflow

  1. Read docs — Fetch HAL documentation with the Documentation tool
  2. Search adapters — Find existing adapters with Actions & Adapters
  3. Build expression — Construct your HAL expression
  4. Simulate — Run with Evaluate Arbitrary or Evaluate Existing
  5. Inspect — Check oplog and use Query Transaction on simulated hashes
  6. Iterate — Fix issues and simulate again
  7. Publish — Once validated, publish via Actions & Adapters

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Next Steps

Query Transaction

Inspect simulated transactions

HAL Reference

Full HAL language documentation