Types and Data

-- TypesAndData.daml
module TypesAndData where

-- ── Record type ────────────────────────────────────────
-- Fields are listed under `with`, one per line.
data Address = Address
  with
    street  : Text
    city    : Text
    country : Text
  deriving (Eq, Show)

-- Constructing a record value:
myAddress : Address
myAddress = Address with
  street  = "10 Downing Street"
  city    = "London"
  country = "GB"

-- Field access uses dot notation:
cityName : Text
cityName = myAddress.city   -- "London"

-- Record update creates a new value (records are immutable):
updatedAddress : Address
updatedAddress = myAddress with city = "Edinburgh"


-- ── Variant (sum type) ─────────────────────────────────
-- Each constructor can carry different data.
data Status
  = Active
  | Suspended Text        -- carries a reason
  | Closed (Optional Text)
  deriving (Eq, Show)

-- Pattern matching on a variant:
describeStatus : Status -> Text
describeStatus Active           = "active"
describeStatus (Suspended r)    = "suspended: " <> r
describeStatus (Closed None)    = "closed"
describeStatus (Closed (Some n)) = "closed: " <> n


-- ── Enum (variant with no payloads) ────────────────────
data Currency = USD | EUR | GBP | JPY
  deriving (Eq, Show)


-- ── Built-in types ─────────────────────────────────────
-- Party   : an authenticated ledger identity
-- Text    : UTF-8 string
-- Int     : 64-bit signed integer
-- Decimal : fixed-point number (38 significant digits, 10 decimal places)
-- Bool    : True / False
-- Date    : calendar date (no time zone)
-- Time    : UTC timestamp
-- Optional a : Some value | None
-- ContractId T : reference to an active contract of template T
-- [a]    : homogeneous list

Key points

Records & variants

• data defines both records (one constructor, fields) and variants (multiple constructors).
• Record update syntax (with field = newValue) creates a new value without mutating the original.
• All composite types must be passed as template parameters; they cannot be stored as global state.

Safety & display

• Optional a is DAML's null-safety type: Some x or None. There is no null.
• Decimal is the correct type for monetary and quantity values: never Double.
• deriving (Eq, Show) generates ==, /=, and show automatically.