Deriving instances

wireform provides two ways to derive encode/decode instances for your types.

Template Haskell deriver (recommended)

Each format ships a Derive module with a TH splice that reads ANN pragmas from the shared wireform-derive annotation vocabulary. This is the only path that supports field renaming, tagging, skipping, and backend-specific overrides:

{-# LANGUAGE TemplateHaskell #-}
import Wireform.Derive (renameStyle, SnakeCase)
import MsgPack.Derive (deriveMsgPack)
import CBOR.Derive (deriveCBOR)

data User = User
  { userName :: !Text
  , userAge  :: !Int
  , userRole :: !Text
  }

{-# ANN type User (renameStyle SnakeCase) #-}

deriveMsgPack ''User
deriveCBOR ''User

Both formats see user_name, user_age, and user_role on the wire, driven by the same annotation.

Generic defaults (no annotations)

Every format’s typeclass has DefaultSignatures that delegate to GHC.Generics. If you don’t need any customization, write empty instance declarations:

{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics (Generic)
import MsgPack.Class (ToMsgPack, FromMsgPack)

data User = User
  { userName :: !Text
  , userAge  :: !Int
  } deriving stock (Show, Eq, Generic)

instance ToMsgPack User
instance FromMsgPack User

Field names go to the wire verbatim. The wireform-derive annotation vocabulary has no effect on this path.

Full annotation reference

See wireform-derive for the complete annotation vocabulary: rename, renameStyle, tag, skip, flatten, defaults, optional, required, coerced, wireOverride, forBackend, and extension.

Format-specific derivers

Format	TH deriver	Module
MessagePack	`deriveMsgPack`	`MsgPack.Derive`
CBOR	`deriveCBOR`	`CBOR.Derive`
YAML	`deriveYAML`	`YAML.Derive`
TOML	`deriveTOML`	`TOML.Derive`
XML	`deriveXML`	`XML.Derive`
HTML	`deriveHTML`	`HTML.Derive`
BSON	`deriveBSON`	`BSON.Derive`
Ion	`deriveIon`	`Ion.Derive`
EDN	`deriveEDN`	`EDN.Derive`
Bencode	`deriveBencode`	`Bencode.Derive`
CSV	`deriveCSV`	`CSV.Derive`
Fory	`deriveFory`	`Fory.Derive`
Thrift	`deriveThrift`	`Thrift.Derive`
Avro	`deriveAvro`	`Avro.Derive`
Bond	`deriveBond`	`Bond.Derive`
FlatBuffers	`deriveFlatBuffers`	`FlatBuffers.Derive`
Cap’n Proto	`deriveCapnProto`	`CapnProto.Derive`
ASN.1	`deriveASN1`	`ASN1.Derive`
Aeson (JSON)	`deriveJSON`	`Wireform.Derive.Aeson`