module Plutarch.Docs.PDataSumAndRecord (Foo (..), test) where 
import Plutarch.Prelude

PDataSum & PDataRecord

Plutarch sum and product types are represented using PDataSum and PDataRecord respectively. These types are crucial to the PIsDataRepr machinery.

Whenever you need to represent a non-trivial ADT using Data encoding, you’ll likely be reaching for these.

More often than not, you’ll be using PDataRecord. This is used to denote all the fields of a constructor:

newtype Foo (s :: S) = Foo (Term s (PDataRecord '["fooField" ':= PInteger]))

Foo is a Plutarch type with a single constructor with a single field, named fooField, of type PInteger. You can implement PlutusType via Data for it so that `PAsData Foo` is represented as a `Constr` encoded data value.

You can build PDataRecord terms using pdcons and pdnil. These are the familiar cons and nil but for PDataRecord terms.

pdcons :: forall label a l s. Term s (PAsData a :--> PDataRecord l :--> PDataRecord ((label ':= a) ': l))

pdnil :: forall s. Term s (PDataRecord '[])

To add an a to the PDataRecord term, you must have a PAsData a. The other type variable of interest, is label. This is just the name of the field you’re adding. You can either use type application to specify the field, or use a type annotation, or let GHC match up the types.

Here’s how you’d build a PDataRecord with two integer fields, one is named foo, the other is named bar:

test :: Term s (PDataRecord '[ "foo" ':= PInteger, "bar" ':= PInteger])
test = pdcons # pdata 7 #$ pdcons # pdata 42 # pdnil

PDataSum on the other hand, is more “free-standing”. In particular, the following type:

PDataSum
  [ '[ "_0" ':= PInteger
     , "_1" ':= PByteString
     ]
  , '[ "myField" ':= PBool
     ]
  ]

represents a sum type with 2 constructors. The first constructor has two fields- _0, and _1, with types PInteger and PByteString respectively. The second constructor has one field- myField, with type PBool.

Note: It’s convention to give names like _0, _1 etc. to fields that don’t have a canonically meaningful name. They are merely the “0th field”, “1st field” etc.

Note: The underlying datatype for PDataRecords and PDataSums are builtin list and constr + builtin lists respectively.