vvm/examples/15-error-values.vvm at main · karanchawla/vvm · GitHub

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# VVM Example 15: Error Values
# Handling errors as first-class values for graceful degradation

agent backup_api(model="sonnet", prompt="Backup payment processor.")
agent logger(model="haiku", prompt="Log events concisely.")

payment = {
  amount: 99.99,
  currency: "USD",
  customer_id: "cust_12345"
}

# Simulate a flaky primary API - realistically weighted toward failures
# In production, this would be a real @api_agent call that might fail
choose payment by ?`simulate flaky payment API: 60% timeout, 20% rejected, 10% spawn_failed, 10% success` as outcome:
  option "timeout":
    result = { error: { kind: "timeout", message: "Connection timed out" } }
  option "rejected":
    result = { error: { kind: "rejected", message: "Card declined" } }
  option "spawn_failed":
    result = { error: { kind: "spawn_failed", message: "Service unavailable" } }
  option "success":
    result = { transaction_id: "txn_abc123", status: "succeeded", amount: payment.amount }

# Errors are values that can be pattern matched
# This enables graceful degradation with fallbacks
match result:
  case error(kind="timeout"):
    # Primary timed out - failover to backup
    @logger `Payment timeout, trying backup.`(payment)
    result = @backup_api `Process: {payment}`(payment, timeout="15s")

  case error(kind="rejected"):
    # Payment was rejected (declined card, etc.)
    @logger `Payment rejected.`(payment)
    result = {
      status: "declined",
      message: "Card declined",
      retry_allowed: false
    }

  case error(kind="spawn_failed"):
    # Agent infrastructure error
    @logger `Service unavailable.`(payment)
    result = {
      status: "error",
      message: "Try again later",
      retry_allowed: true
    }

  case error(e):
    # Catch-all for unexpected errors
    @logger `Unexpected error: {e}`(e)
    result = {
      status: "error",
      message: "Unknown error",
      details: e
    }

  case _:
    # Success - log and continue
    @logger `Payment successful: {result}`(result)

# Final safety check - if backup also failed, return safe default
if ?`is an error value`(result):
  result = {
    status: "failed",
    message: "All processors unavailable",
    retry_allowed: true,
    original_error: result
  }

export result