Maybe wrapper for abi decoding

[cmditch]

You might see mappings like this

isAdmin(address => bool)
adminAuthLevel(address => uint)

But they can be combined like so, and represented on the front end with a Maybe

isAdmin(address => uint) // returns the admins auth level, or 0 if is not an admin.

Maybe's tell us not only if something exists, but also what exists if so. It conveys multiple states in one data type. We can convey the information of two maps in one, by cleverly defining 0 as one distinct type of state, and 1..n as another type of state.

type alias AuthLevel = BigInt

isAdmin : AbiDecoder (Maybe AuthLevel)
isAdmin =
    Abi.maybe Abi.uint

Abi.maybe might look something like.

maybe : AbiDecoder a -> AbiDecoder (Maybe a)
maybe decoder =
    AbiDecoder <|
        \returnBlob -> 
            case returnBlob of
                0x000... -> Nothing
                n -> Just (decoder n)