How to convert BuiltinData to BuiltinString?

Question

Since I just started to write Plutus code, I want to make some tests of Plutus.

For example, I'd like to know what exactly my redeemer :: BuiltinData value is. However I can't convert BuiltinData to BuiltinString which means I can't use trace :: BuiltinString -> a -> a to log it.

Is it possible to convert BuiltinData to BuiltinString or there is different approach to log redeemer?

Answer 1

Since BuiltinData derives Show:

newtype BuiltinData = BuiltinData PLC.Data
    deriving newtype (Show, Eq, Ord)

and there's the function:

stringToBuiltinString :: String -> BuiltinString found here in PlutusTx/Builtins/Class.hs

Assuming your "variable name" is dummyBuiltinData, you can convert BuiltinData to BuiltinString using:

stringToBuiltinString $ show dummyBuiltinData

EDIT:

As noted by kolam, show isn't INLINABLE and isn't applicable on-chain. Here is a version that should work:

decodeUtf8 $ unsafeDataAsB dummyBuiltinData

both decodeUtf8 and unsafeDataAsB can be found in module PlutusTx.Builtins.Internal

Answer 2

You can't print out strings that are built at runtime in onchain code with Plutus, my guess is that's because the script's address is generated by hashing the validator function, so it only allows hardcoded strings so the hash of that function is always the same.

My solution is to trigger traceIfFalse with a function that gives me a clue about the variable I'm investigating:

... 
mkValidator = traceIfFalse getTraceString False 

getTraceString :: BuiltinString
getTraceString = case someVar of 
                   a -> "it's a"
                   b -> "it's b"
                   _ -> "it's something else"
...

A bit kludgy, but it's working for me.