is-ok

Function Signature

(is-ok value)

• Input: (response A B)
• Output: bool

Why it matters

The is-ok function is crucial for:

1. Determining if a response value represents a successful operation.
2. Implementing conditional logic based on the success or failure of operations.
3. Ensuring robust contract behavior by checking for successful responses.
4. Simplifying checks for response types in smart contract code.

When to use it

Use is-ok when you need to:

• Check if a response value is ok.
• Implement logic that depends on the success of operations.
• Validate the results of function calls that return response types.
• Handle success cases gracefully in your contract logic.

Best Practices

• Use is-ok in combination with match or if for comprehensive response handling.
• Ensure that the response value being checked is of the correct type.
• Use meaningful variable names for better readability.
• Combine with other response handling functions like is-err for complete validation.

Practical Example: Validating a Token Transfer

Let's implement a function that validates a token transfer and checks for success:

(define-map UserBalances { userId: principal } { balance: uint })

(define-public (transfer-tokens (amount uint) (recipient principal))
  (let
    (
      (senderBalance (default-to u0 (map-get? UserBalances { userId: tx-sender })))
      (recipientBalance (default-to u0 (map-get? UserBalances { userId: recipient })))
      (transferResult (if (>= senderBalance amount)
        (begin
          (map-set UserBalances { userId: tx-sender } { balance: (- senderBalance amount) })
          (map-set UserBalances { userId: recipient } { balance: (+ recipientBalance amount) })
          (ok true)
        )
        (err u1)
      ))
    )
    (if (is-ok transferResult)
      (ok true)
      (err u2)
    )
  )
)

;; Usage
(map-set UserBalances { userId: tx-sender } { balance: u100 })
(transfer-tokens u50 'SPAXYA5XS51713FDTQ8H94EJ4V579CXMTRNBZKSF) ;; Returns (ok true)
(transfer-tokens u200 'SPAXYA5XS51713FDTQ8H94EJ4V579CXMTRNBZKSF) ;; Returns (err u2)

This example demonstrates:

1. Using is-ok to check if the token transfer operation was successful.
2. Implementing conditional logic based on the success of the transfer.
3. Handling both the success and error cases appropriately.

Common Pitfalls

1. Assuming the response value is always of the correct type, leading to type errors.
2. Not handling all possible success and error cases, resulting in incomplete response handling.
3. Overlooking the need for comprehensive validation and error checking.
4. Using is-ok without meaningful success codes or messages, making debugging harder.

Related Functions

• is-err: Checks if a response value is err.
• err: Constructs an error response.
• ok: Constructs a success response.

Conclusion

The is-ok function is a fundamental tool for checking response values in Clarity smart contracts. It allows developers to determine if a response value represents a successful operation, enabling robust and comprehensive response handling and validation logic. When used effectively, is-ok enhances the reliability and maintainability of your smart contract code by ensuring that successful operations are detected and handled appropriately.