Return Types

bs-decode provides decode functions that will return values wrapped in either an option or a result. Many of these error handling ideas were inspired by Composable Error Handling in OCaml, which is a great read that goes into more detail than our summary here.

• Decode.AsResult.OfParseError: all functions return Ok(value) for success, or Error(Decode.ParseError.t) for failures
• Decode.AsResult.OfStringNel: all functions return Ok(value) for success, or Error(NonEmptyList.t(string)) for failures
• Decode.AsOption: all functions return Some(value) for success or None for failures

Result of ParseError

While it's possible to choose other error representations when using bs-decode, this is the preferred choice for decoding, as it provides the richest error information. In a future release, this will be the only supported value for holding the decode output.

For more information on how to work with the structured error data returned by these decoders, see Working With Errors.

Option (Deprecated)

If you prefer to work with option for the sake of simplicity, it's recommended that you still use Decode.AsResult.OfParseError and convert the result to option after running the decoder.

Result of NonEmptyList String (Deprecated)

Instead of providing structured, typed error information when a decoder fails, Decode.AsResult.OfStringNel returns a non-empty list of string error messages. The benefit is that string error messages are easy to read and easy to extend with your own validation error messages. However, the error messages provided aren't as rich in information as the errors when using Decode.AsResult.OfParseError, and if your goal is simply to read the output, it's better to use those decoders and convert the error messages to a string using Decode.ParseError.failureToDebugString.

We're hoping to reduce the need for custom error messages (the biggest benefit of using this set of decoders), and maintaining multiple types of result decoders adds quite a bit of complexity to the bs-decode library, so this set of decoders will likely be removed in a future release.