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Prelude

The pieces that make up the Daml language.

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Module Snapshot

Lifecycle

Stable.

Notices

Status: active Introduced in: 3.4.9 Removed in: - Warnings: 0 Deprecations: 0 Deprecated since: -

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Data Types

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data AnyChoice

Existential choice type that can wrap an arbitrary choice. Constructors:
  • AnyChoice
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Any
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TemplateTypeRep
Instances:

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data AnyTemplate

Existential template type that can wrap an arbitrary template. Constructors:
  • AnyTemplate
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Any
Instances:

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data TemplateTypeRep

Unique textual representation of a template Id. Constructors:
  • TemplateTypeRep
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TypeRep
Instances:

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data Down a

The Down type can be used for reversing sorting order. For example, sortOn (\x -> Down x.field) would sort by descending field. Constructors:
  • Down a
Instances:

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type Implements t i

= (HasInterfaceTypeRep i, HasToInterface t i, HasFromInterface t i) (Daml-LF >= 1.15) Constraint that indicates that a template implements an interface.

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data AnyException

A wrapper for all exception types.
Deprecated: Exceptions are deprecated, prefer failWithStatus, and avoid using catch.
Deprecated: Use -Wno-deprecated-exceptions to disable this warning.
Instances:

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data ContractId a

The ContractId a type represents an ID for a contract created from a template a. You can use the ID to fetch the contract, among other things. Instances:

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data Date

The Date type represents a date, for example date 2007 Apr 5. The bounds for Date are 0001-01-01 and 9999-12-31. Instances:

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data Map a b

The Map a b type represents an associative array from keys of type a to values of type b. It uses the built-in equality for keys. Import DA.Map to use it. Instances:

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data Party

The Party type represents a party to a contract. Instances:

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data TextMap a

The TextMap a type represents an associative array from keys of type Text to values of type a. Instances:

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data Time

The Time type represents a specific datetime in UTC, for example time (date 2007 Apr 5) 14 30 05. The bounds for Time are 0001-01-01T00:00:00.000000Z and 9999-12-31T23:59:59.999999Z. Instances:

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data Update a

The Update a type represents an Action to update or query the ledger, before returning a value of type a. Examples include create and fetch. Instances:

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data Optional a

The Optional type encapsulates an optional value. A value of type Optional a either contains a value of type a (represented as Some a), or it is empty (represented as None). Using Optional is a good way to deal with errors or exceptional cases without resorting to drastic measures such as error. The Optional type is also an Action. It is a simple kind of error Action, where all errors are represented by None. A richer error Action could be built using the Data.Either.Either type. Constructors:
  • None
  • Some a
Instances:

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data Archive

The data type corresponding to the implicit Archive choice in every template. Constructors:
  • Archive
(no fields) Instances:

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type Choice t c r

= (Template t, HasExercise t c r, HasToAnyChoice t c r, HasFromAnyChoice t c r) Constraint satisfied by choices.

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type Template t

= (HasTemplateTypeRep t, HasToAnyTemplate t, HasFromAnyTemplate t)

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type TemplateKey t k

= (Template t, HasKey t k, HasFetchByKey t k, HasMaintainer t k) Constraint satisfied by template keys.

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data Either a b

The Either type represents values with two possibilities: a value of type Either a b is either Left a or Right b. The Either type is sometimes used to represent a value which is either correct or an error; by convention, the Left constructor is used to hold an error value and the Right constructor is used to hold a correct value (mnemonic: “right” also means “correct”). Constructors:
  • Left a
  • Right b
Instances:

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type ShowS

= Text -> Text showS should represent some text, and applying it to some argument should prepend the argument to the represented text.

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data Bool

A type for Boolean values, ie True and False. Constructors:
  • False
  • True
Instances:

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type Decimal

= Numeric 10

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data Int

A type representing a 64-bit integer. Instances:

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data Nat

(Kind) This is the kind of type-level naturals.

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data Numeric n

A type for fixed-point decimal numbers, with the scale being passed as part of the type. Numeric n represents a fixed-point decimal number with a fixed precision of 38 (i.e. 38 digits not including a leading zero) and a scale of n, i.e., n digits after the decimal point. n must be between 0 and 37 (bounds inclusive). Examples:
Instances:

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data Ordering

A type for giving information about ordering: being less than (LT), equal to (EQ), or greater than (GT) something. Constructors:
  • LT
  • EQ
  • GT
Instances:

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data Text

A type for text strings, that can represent any unicode code point. For example "Hello, world". Instances:

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data [] a

A type for lists, for example [1,2,3]. Constructors:
  • []
  • : _ _

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Typeclasses

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class Action m => CanAssert m

Constraint that determines whether an assertion can be made in this context. Methods:
  • assertFail : Text -> m t Abort since an assertion has failed. In an Update, Scenario, or Script context this will throw an AssertionFailed exception. In an Either Text context, this will return the message as an error.
Instances:

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class HasInterfaceTypeRep i

(Daml-LF >= 1.15) Exposes the interfaceTypeRep function. Available only for interfaces.

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class HasToInterface t i

(Daml-LF >= 1.15) Exposes the toInterface and toInterfaceContractId functions.

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class HasFromInterface t i

(Daml-LF >= 1.15) Exposes fromInterface and fromInterfaceContractId functions. Methods:
  • fromInterface : i -> Optional t (Daml-LF >= 1.15) Attempt to convert an interface value back into a template value. A None indicates that the expected template type doesn’t match the underyling template type for the interface value. For example, fromInterface @MyTemplate value will try to convert the interface value value into the template type MyTemplate.

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class HasInterfaceView i v

Methods:
  • _view : i -> v

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class HasTime m

The HasTime class is for where the time is available: Update Methods: Instances:

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class Action m => CanAbort m

The CanAbort class is for Action s that can be aborted. Methods:
  • abort : Text -> m a Abort the current action with a message.
Instances:

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class Functor f => Applicative f

Methods:
  • pure : a -> f a Lift a value.
  • <*> : f (a -> b) -> f a -> f b Sequentially apply the function. A few functors support an implementation of <*> that is more efficient than the default one.
  • liftA2 : (a -> b -> c) -> f a -> f b -> f c Lift a binary function to actions. Some functors support an implementation of liftA2 that is more efficient than the default one. In particular, if fmap is an expensive operation, it is likely better to use liftA2 than to fmap over the structure and then use <*>.
  • *> : f a -> f b -> f b Sequence actions, discarding the value of the first argument.
  • <* : f a -> f b -> f a Sequence actions, discarding the value of the second argument.
Instances:

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class Applicative m => Action m

Methods:
  • >>= : m a -> (a -> m b) -> m b Sequentially compose two actions, passing any value produced by the first as an argument to the second.
Instances:

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class Action m => ActionFail m

This class exists to desugar pattern matches in do-notation. Polymorphic usage, or calling fail directly, is not recommended. Instead consider using CanAbort. Methods:
  • fail : Text -> m a Fail with an error message.
Instances:

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class Semigroup a

The class of semigroups (types with an associative binary operation). Methods:
  • <> : a -> a -> a An associative operation.
Instances:

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class Semigroup a => Monoid a

The class of monoids (types with an associative binary operation that has an identity). Methods:
  • mempty : a Identity of (<>)
  • mconcat : [a] -> a Fold a list using the monoid. For example using mconcat on a list of strings would concatenate all strings to one lone string.
Instances:

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class HasSignatory t

Exposes signatory function. Part of the Template constraint. Methods:
  • signatory : t -> [Party] The signatories of a contract.

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class HasObserver t

Exposes observer function. Part of the Template constraint. Methods:
  • observer : t -> [Party] The observers of a contract.

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class HasEnsure t

Exposes ensure function. Part of the Template constraint. Methods:
  • ensure : t -> Bool A predicate that must be true, otherwise contract creation will fail.

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class HasCreate t

Exposes create function. Part of the Template constraint. Methods:

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class HasFetch t

Exposes fetch function. Part of the Template constraint. Methods:
  • fetch : ContractId t -> Update t Fetch the contract data associated with the given contract ID. If the ContractId t supplied is not the contract ID of an active contract, this fails and aborts the entire transaction.

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class HasSoftFetch t

Exposes softFetch function

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class HasSoftExercise t c r

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class HasArchive t

Exposes archive function. Part of the Template constraint. Methods:
  • archive : ContractId t -> Update () Archive the contract with the given contract ID.

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class HasTemplateTypeRep t

Exposes templateTypeRep function in Daml-LF 1.7 or later. Part of the Template constraint.

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class HasToAnyTemplate t

Exposes toAnyTemplate function in Daml-LF 1.7 or later. Part of the Template constraint.

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class HasFromAnyTemplate t

Exposes fromAnyTemplate function in Daml-LF 1.7 or later. Part of the Template constraint.

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class HasExercise t c r

Exposes exercise function. Part of the Choice constraint. Methods:
  • exercise : ContractId t -> c -> Update r Exercise a choice on the contract with the given contract ID.

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class HasChoiceController t c

Exposes choiceController function. Part of the Choice constraint.

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class HasChoiceObserver t c

Exposes choiceObserver function. Part of the Choice constraint.

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class HasExerciseGuarded t c r

(1.dev only) Exposes exerciseGuarded function. Only available for interface choices. Methods:
  • exerciseGuarded : (t -> Bool) -> ContractId t -> c -> Update r (1.dev only) Exercise a choice on the contract with the given contract ID, only if the predicate returns True.

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class HasToAnyChoice t c r

Exposes toAnyChoice function for Daml-LF 1.7 or later. Part of the Choice constraint.

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class HasFromAnyChoice t c r

Exposes fromAnyChoice function for Daml-LF 1.7 or later. Part of the Choice constraint.

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class HasKey t k

Exposes key function. Part of the TemplateKey constraint. Methods:
  • key : t -> k The key of a contract.

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class HasLookupByKey t k

Exposes lookupByKey function. Part of the TemplateKey constraint.

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class HasFetchByKey t k

Exposes fetchByKey function. Part of the TemplateKey constraint.

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class HasLookupNByKey t k

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class HasMaintainer t k

Exposes maintainer function. Part of the TemplateKey constraint.

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class HasExerciseByKey t k c r

Exposes exerciseByKey function.

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class IsParties a

Accepted ways to specify a list of parties: either a single party, or a list of parties. Methods:
  • toParties : a -> [Party] Convert to list of parties.
Instances:

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class Functor f

A Functor is a typeclass for things that can be mapped over (using its fmap function. Examples include Optional, [] and Update). Methods:
  • fmap : (a -> b) -> f a -> f b fmap takes a function of type a -> b, and turns it into a function of type f a -> f b, where f is the type which is an instance of Functor. For example, map is an fmap that only works on lists. It takes a function a -> b and a [a], and returns a [b].
  • <$ : a -> f b -> f a Replace all locations in the input f b with the same value a. The default definition is fmap . const, but you can override this with a more efficient version.

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class Eq a

The Eq class defines equality (==) and inequality (/=). All the basic datatypes exported by the “Prelude” are instances of Eq, and Eq may be derived for any datatype whose constituents are also instances of Eq. Usually, == is expected to implement an equivalence relationship where two values comparing equal are indistinguishable by “public” functions, with a “public” function being one not allowing to see implementation details. For example, for a type representing non-normalised natural numbers modulo 100, a “public” function doesn’t make the difference between 1 and 201. It is expected to have the following properties: Reflexivity: x == x = True Symmetry: x == y = y == x Transitivity: if x == y && y == z = True, then x == z = True Substitutivity: if x == y = True and f is a “public” function whose return type is an instance of Eq, then f x == f y = True Negation: x /= y = not (x == y) Minimal complete definition: either == or /=. Methods:
  • == : a -> a -> Bool
  • /= : a -> a -> Bool
Instances:

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class Eq a => Ord a

The Ord class is used for totally ordered datatypes. Instances of Ord can be derived for any user-defined datatype whose constituent types are in Ord. The declared order of the constructors in the data declaration determines the ordering in derived Ord instances. The Ordering datatype allows a single comparison to determine the precise ordering of two objects. The Haskell Report defines no laws for Ord. However, <= is customarily expected to implement a non-strict partial order and have the following properties: Transitivity: if x <= y && y <= z = True, then x <= z = True Reflexivity: x <= x = True Antisymmetry: if x <= y && y <= x = True, then x == y = True Note that the following operator interactions are expected to hold:
  1. x >= y = y <= x
  2. x < y = x <= y && x /= y
  3. x > y = y < x
  4. x < y = compare x y == LT
  5. x > y = compare x y == GT
  6. x == y = compare x y == EQ
  7. min x y == if x <= y then x else y = ‘True’
  8. max x y == if x >= y then x else y = ‘True’
Minimal complete definition: either compare or <=. Using compare can be more efficient for complex types. Methods:
  • compare : a -> a -> Ordering
  • < : a -> a -> Bool
  • <= : a -> a -> Bool
  • > : a -> a -> Bool
  • >= : a -> a -> Bool
  • max : a -> a -> a
  • min : a -> a -> a
Instances:

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class NumericScale n

Is this a valid scale for the Numeric type? This typeclass is used to prevent the creation of Numeric values with too large a scale. The scale controls the number of digits available after the decimal point, and it must be between 0 and 37 inclusive. Thus the only available instances of this typeclass are NumericScale 0 through NumericScale 37. This cannot be extended without additional compiler and runtime support. You cannot implement a custom instance of this typeclass. If you have an error message in your code of the form “No instance for (NumericScale n)”, this is probably caused by having a numeric literal whose scale cannot be inferred by the compiler. You can usually fix this by adding a type signature to the definition, or annotating the numeric literal directly (for example, instead of writing 3.14159 you can write (3.14159 : Numeric 5)). Methods:
  • numericScale : Int Get the scale of a Numeric as an integer. For example, numericScale (3.14159 : Numeric 5) equals 5.
  • numericOne : Numeric n 1 with scale n
Instances:

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class Bounded a

Use the Bounded class to name the upper and lower limits of a type. You can derive an instance of the Bounded class for any enumeration type. minBound is the first constructor listed in the data declaration and maxBound is the last. You can also derive an instance of Bounded for single-constructor data types whose constituent types are in Bounded. Ord is not a superclass of Bounded because types that are not totally ordered can still have upper and lower bounds. Methods:
  • minBound : a
  • maxBound : a
Instances:

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class Enum a

Use the Enum class to define operations on sequentially ordered types: that is, types that can be enumerated. Enum members have defined successors and predecessors, which you can get with the succ and pred functions. Types that are an instance of class Bounded as well as Enum should respect the following laws:
  • Both succ maxBound and pred minBound should result in a runtime error.
  • fromEnum and toEnum should give a runtime error if the result value is not representable in the result type. For example, toEnum 7 : Bool is an error.
  • enumFrom and enumFromThen should be defined with an implicit bound, like this:
Methods:
  • succ : a -> a Returns the successor of the given value. For example, for numeric types, succ adds 1. If the type is also an instance of Bounded, succ maxBound results in a runtime error.
  • pred : a -> a Returns the predecessor of the given value. For example, for numeric types, pred subtracts 1. If the type is also an instance of Bounded, pred minBound results in a runtime error.
  • toEnum : Int -> a Convert a value from an Int to an Enum value: ie, toEnum i returns the item at the i th position of (the instance of) Enum
  • fromEnum : a -> Int Convert a value from an Enum value to an Int: ie, returns the Int position of the element within the Enum. If fromEnum is applied to a value that’s too large to fit in an Int, what is returned is up to your implementation.
  • enumFrom : a -> [a] Return a list of the Enum values starting at the Int position. For example:
    • enumFrom 6 : [Int] = [6,7,8,9,...,maxBound : Int]
  • enumFromThen : a -> a -> [a] Returns a list of the Enum values with the first value at the first Int position, the second value at the second Int position, and further values with the same distance between them. For example:
    • enumFromThen 4 6 : [Int] = [4,6,8,10...]
    • enumFromThen 6 2 : [Int] = [6,2,-2,-6,...,minBound :: Int]
  • enumFromTo : a -> a -> [a] Returns a list of the Enum values with the first value at the first Int position, and the last value at the last Int position. This is what’s behind the language feature that lets you write [n,m..]. For example:
    • enumFromTo 6 10 : [Int] = [6,7,8,9,10]
  • enumFromThenTo : a -> a -> a -> [a] Returns a list of the Enum values with the first value at the first Int position, the second value at the second Int position, and further values with the same distance between them, with the final value at the final Int position. This is what’s behind the language feature that lets you write [n,n'..m]. For example:
    • enumFromThenTo 4 2 -6 : [Int] = [4,2,0,-2,-4,-6]
    • enumFromThenTo 6 8 2 : [Int] = []
Instances:

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class Additive a

Use the Additive class for types that can be added. Instances have to respect the following laws:
  • (+) must be associative, ie: (x + y) + z = x + (y + z)
  • (+) must be commutative, ie: x + y = y + x
  • x + aunit = x
  • negate gives the additive inverse, ie: x + negate x = aunit
Methods:
  • + : a -> a -> a Add the two arguments together.
  • aunit : a The additive identity for the type. For example, for numbers, this is 0.
  • - : a -> a -> a Subtract the second argument from the first argument, ie. x - y = x + negate y
  • negate : a -> a Negate the argument: x + negate x = aunit
Instances:

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class Multiplicative a

Use the Multiplicative class for types that can be multiplied. Instances have to respect the following laws:
  • (*) is associative, ie:(x * y) * z = x * (y * z)
  • (*) is commutative, ie: x * y = y * x
  • x * munit = x
Methods:
  • * : a -> a -> a Multipy the arguments together
  • munit : a The multiplicative identity for the type. For example, for numbers, this is 1.
  • ^ : a -> Int -> a x ^ n raises x to the power of n.
Instances:

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class (Additive a, Multiplicative a) => Number a

Number is a class for numerical types. As well as the rules for Additive and Multiplicative, instances also have to respect the following law:
  • (*) is distributive with respect to (+). That is: a * (b + c) = (a * b) + (a * c) and (b + c) * a = (b * a) + (c * a)
Instances:

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class Signed a

The Signed is for the sign of a number. Methods:
  • signum : a -> a Sign of a number. For real numbers, the ‘signum’ is either -1 (negative), 0 (zero) or 1 (positive).
  • abs : a -> a The absolute value: that is, the value without the sign.
Instances:

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class Multiplicative a => Divisible a

Use the Divisible class for types that can be divided. Instances should respect that division is the inverse of multiplication, i.e. x * y / y is equal to x whenever it is defined. Methods:
  • / : a -> a -> a x / y divides x by y
Instances:

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class Divisible a => Fractional a

Use the Fractional class for types that can be divided and where the reciprocal is well defined. Instances have to respect the following laws:
  • When recip x is defined, it must be the inverse of x with respect to multiplication: x * recip x = munit
  • When recip y is defined, then x / y = x * recip y
Methods:
  • recip : a -> a Calculates the reciprocal: recip x is 1/x.
Instances:

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class Show a

Use the Show class for values that can be converted to a readable Text value. Derived instances of Show have the following properties:
  • The result of show is a syntactically correct expression that only contains constants (given the fixity declarations in force at the point where the type is declared). It only contains the constructor names defined in the data type, parentheses, and spaces. When labelled constructor fields are used, braces, commas, field names, and equal signs are also used.
  • If the constructor is defined to be an infix operator, then showsPrec produces infix applications of the constructor.
  • If the precedence of the top-level constructor in x is less than d (associativity is ignored), the representation will be enclosed in parentheses. For example, if d is 0 then the result is never surrounded in parentheses; if d is 11 it is always surrounded in parentheses, unless it is an atomic expression.
  • If the constructor is defined using record syntax, then show will produce the record-syntax form, with the fields given in the same order as the original declaration.
Methods:
  • showsPrec : Int -> a -> ShowS Convert a value to a readable Text value. Unlike show, showsPrec should satisfy the rule showsPrec d x r ++ s == showsPrec d x (r ++ s)
  • show : a -> Text Convert a value to a readable Text value.
  • showList : [a] -> ShowS Allows you to show lists of values.
Instances:

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Functions

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assert

assert : CanAssert m => Bool -> m () Check whether a condition is true. If it’s not, abort the transaction.

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assertMsg

assertMsg : CanAssert m => Text -> Bool -> m () Check whether a condition is true. If it’s not, abort the transaction with a message.

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assertAfter

assertAfter : (CanAssert m, HasTime m) => Time -> m () Check whether the given time is in the future. If it’s not, abort the transaction.

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assertBefore

assertBefore : (CanAssert m, HasTime m) => Time -> m () Check whether the given time is in the past. If it’s not, abort the transaction.

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daysSinceEpochToDate

daysSinceEpochToDate : Int -> Date Convert from number of days since epoch (i.e. the number of days since January 1, 1970) to a date.

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dateToDaysSinceEpoch

dateToDaysSinceEpoch : Date -> Int Convert from a date to number of days from epoch (i.e. the number of days since January 1, 1970).

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interfaceTypeRep

interfaceTypeRep : HasInterfaceTypeRep i => i -> TemplateTypeRep (Daml-LF >= 1.15) Obtain the TemplateTypeRep for the template given in the interface value.

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toInterface

toInterface : HasToInterface t i => t -> i (Daml-LF >= 1.15) Convert a template value into an interface value. For example toInterface @MyInterface value converts a template value into a MyInterface type.

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toInterfaceContractId

toInterfaceContractId : HasToInterface t i => ContractId t -> ContractId i (Daml-LF >= 1.15) Convert a template contract id into an interface contract id. For example, toInterfaceContractId @MyInterface cid.

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fromInterfaceContractId

fromInterfaceContractId : HasFromInterface t i => ContractId i -> ContractId t (Daml-LF >= 1.15) Convert an interface contract id into a template contract id. For example, fromInterfaceContractId @MyTemplate cid. Can also be used to convert an interface contract id into a contract id of one of its requiring interfaces. This function does not verify that the interface contract id actually points to a template of the given type. This means that a subsequent fetch, exercise, or archive may fail, if, for example, the contract id points to a contract that implements the interface but is of a different template type than expected. Therefore, you should only use fromInterfaceContractId in situations where you already know that the contract id points to a contract of the right template type. You can also use it in situations where you will fetch, exercise, or archive the contract right away, when a transaction failure is the appropriate response to the contract having the wrong template type. In all other cases, consider using fetchFromInterface instead.

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coerceInterfaceContractId

coerceInterfaceContractId : (HasInterfaceTypeRep i, HasInterfaceTypeRep j) => ContractId i -> ContractId j (Daml-LF >= 1.15) Convert an interface contract id into a contract id of a different interface. For example, given two interfaces Source and Target, and cid : ContractId Source, coerceInterfaceContractId @Target @Source cid : ContractId Target. This function does not verify that the contract id actually points to a contract that implements either interface. This means that a subsequent fetch, exercise, or archive may fail, if, for example, the contract id points to a contract of template A but it was coerced into a ContractId B where B is an interface and there’s no interface instance B for A. Therefore, you should only use coerceInterfaceContractId in situations where you already know that the contract id points to a contract of the right type. You can also use it in situations where you will fetch, exercise, or archive the contract right away, when a transaction failure is the appropriate response to the contract having the wrong type.

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fetchFromInterface

fetchFromInterface : (HasFromInterface t i, HasFetch i) => ContractId i -> Update (Optional (ContractId t, t)) (Daml-LF >= 1.15) Fetch an interface and convert it to a specific template type. If conversion is succesful, this function returns the converted contract and its converted contract id. Otherwise, this function returns None. Can also be used to fetch and convert an interface contract id into a contract and contract id of one of its requiring interfaces. Example:

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_exerciseInterfaceGuard

_exerciseInterfaceGuard : a -> b -> c -> Bool

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view

view : HasInterfaceView i v => i -> v

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partyToText

partyToText : Party -> Text Convert the Party to Text, giving back what you passed to getParty. In most cases, you should use show instead. show wraps the party in 'ticks' making it clear it was a Party originally.

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partyFromText

partyFromText : Text -> Optional Party Converts a Text to Party. It returns None if the provided text contains any forbidden characters. See Daml-LF spec for a specification on which characters are allowed in parties. Note that this function accepts text without single quotes. This function does not check on whether the provided text corresponds to a party that “exists” on a given ledger: it merely converts the given Text to a Party. The only way to guarantee that a given Party exists on a given ledger is to involve it in a contract. This function, together with partyToText, forms an isomorphism between valid party strings and parties. In other words, the following equations hold:
This function will crash at runtime if you compile Daml to Daml-LF < 1.2.

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coerceContractId

coerceContractId : ContractId a -> ContractId b Used to convert the type index of a ContractId, since they are just pointers. Note that subsequent fetches and exercises might fail if the template of the contract on the ledger doesn’t match.

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curry

curry : ((a, b) -> c) -> a -> b -> c Turn a function that takes a pair into a function that takes two arguments.

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uncurry

uncurry : (a -> b -> c) -> (a, b) -> c Turn a function that takes two arguments into a function that takes a pair.

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>>

>> : Action m => m a -> m b -> m b Sequentially compose two actions, discarding any value produced by the first. This is like sequencing operators (such as the semicolon) in imperative languages.

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ap

ap : Applicative f => f (a -> b) -> f a -> f b Synonym for <*>.

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return

return : Applicative m => a -> m a Inject a value into the monadic type. For example, for Update and a value of type a, return would give you an Update a.

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join

join : Action m => m (m a) -> m a Collapses nested actions into a single action.

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identity

identity : a -> a The identity function.

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guard

guard : ActionFail m => Bool -> m ()

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foldl

foldl : (b -> a -> b) -> b -> [a] -> b This function is a left fold, which you can use to inspect/analyse/consume lists. foldl f i xs performs a left fold over the list xs using the function f, using the starting value i. Examples:
Note that foldl works from left-to-right over the list arguments.

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find

find : (a -> Bool) -> [a] -> Optional a find p xs finds the first element of the list xs where the predicate p is true. There might not be such an element, which is why this function returns an Optional a.

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length

length : [a] -> Int Gives the length of the list.

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any

any : (a -> Bool) -> [a] -> Bool Are there any elements in the list where the predicate is true? any p xs is True if p holds for at least one element of xs.

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all

all : (a -> Bool) -> [a] -> Bool Is the predicate true for all of the elements in the list? all p xs is True if p holds for every element of xs.

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or

or : [Bool] -> Bool Is at least one of elements in a list of Bool true? or bs is True if at least one element of bs is True.

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and

and : [Bool] -> Bool Is every element in a list of Bool true? and bs is True if every element of bs is True.

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elem

elem : Eq a => a -> [a] -> Bool Does this value exist in this list? elem x xs is True if x is an element of the list xs.

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notElem

notElem : Eq a => a -> [a] -> Bool Negation of elem: elem x xs is True if x is not an element of the list xs.

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<$>

<$> : Functor f => (a -> b) -> f a -> f b Synonym for fmap.

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optional

optional : b -> (a -> b) -> Optional a -> b The optional function takes a default value, a function, and a Optional value. If the Optional value is None, the function returns the default value. Otherwise, it applies the function to the value inside the Some and returns the result. Basic usage examples:
This example applies show to a Optional Int. If you have Some n, this shows the underlying Int, n. But if you have None, this returns the empty string instead of (for example) None:

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either

either : (a -> c) -> (b -> c) -> Either a b -> c The either function provides case analysis for the Either type. If the value is Left a, it applies the first function to a; if it is Right b, it applies the second function to b. Examples: This example has two values of type Either [Int] Int, one using the Left constructor and another using the Right constructor. Then it applies either the length function (if it has a [Int]) or the “times-two” function (if it has an Int):

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concat

concat : [[a]] -> [a] Take a list of lists and concatenate those lists into one list.

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++

++ : [a] -> [a] -> [a] Concatenate two lists.

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flip

flip : (a -> b -> c) -> b -> a -> c Flip the order of the arguments of a two argument function.

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reverse

reverse : [a] -> [a] Reverse a list.

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mapA

mapA : Applicative m => (a -> m b) -> [a] -> m [b] Apply an applicative function to each element of a list.

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forA

forA : Applicative m => [a] -> (a -> m b) -> m [b] forA is mapA with its arguments flipped.

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sequence

sequence : Applicative m => [m a] -> m [a] Perform a list of actions in sequence and collect the results.

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=<<

=<< : Action m => (a -> m b) -> m a -> m b =<< is >>= with its arguments flipped.

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concatMap

concatMap : (a -> [b]) -> [a] -> [b] Map a function over each element of a list, and concatenate all the results.

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replicate

replicate : Int -> a -> [a] replicate i x gives the list [x, x, x, ..., x] with i copies of x.

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take

take : Int -> [a] -> [a] Take the first n elements of a list.

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drop

drop : Int -> [a] -> [a] Drop the first n elements of a list.

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splitAt

splitAt : Int -> [a] -> ([a], [a]) Split a list at a given index.

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takeWhile

takeWhile : (a -> Bool) -> [a] -> [a] Take elements from a list while the predicate holds.

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dropWhile

dropWhile : (a -> Bool) -> [a] -> [a] Drop elements from a list while the predicate holds.

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span

span : (a -> Bool) -> [a] -> ([a], [a]) span p xs is equivalent to (takeWhile p xs, dropWhile p xs).

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partition

partition : (a -> Bool) -> [a] -> ([a], [a]) The partition function takes a predicate, a list and returns the pair of lists of elements which do and do not satisfy the predicate, respectively; i.e.,
partition p xs == (filter p xs, filter (not . p) xs)

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break

break : (a -> Bool) -> [a] -> ([a], [a]) Break a list into two, just before the first element where the predicate holds. break p xs is equivalent to span (not . p) xs.

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lookup

lookup : Eq a => a -> [(a, b)] -> Optional b Look up the first element with a matching key.

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enumerate

enumerate : (Enum a, Bounded a) => [a] Generate a list containing all values of a given enumeration.

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zip

zip : [a] -> [b] -> [(a, b)] zip takes two lists and returns a list of corresponding pairs. If one list is shorter, the excess elements of the longer list are discarded.

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zip3

zip3 : [a] -> [b] -> [c] -> [(a, b, c)] zip3 takes three lists and returns a list of triples, analogous to zip.

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zipWith

zipWith : (a -> b -> c) -> [a] -> [b] -> [c] zipWith takes a function and two lists. It generalises zip by combining elements using the function, instead of forming pairs. If one list is shorter, the excess elements of the longer list are discarded.

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zipWith3

zipWith3 : (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] zipWith3 generalises zip3 by combining elements using the function, instead of forming triples.

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unzip

unzip : [(a, b)] -> ([a], [b]) Turn a list of pairs into a pair of lists.

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unzip3

unzip3 : [(a, b, c)] -> ([a], [b], [c]) Turn a list of triples into a triple of lists.

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traceRaw

traceRaw : Text -> a -> a traceRaw msg a prints msg and returns a, for debugging purposes. The default configuration on the participant logs these messages at DEBUG level.

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trace

trace : Show b => b -> a -> a trace b a prints b and returns a, for debugging purposes. The default configuration on the participant logs these messages at DEBUG level.

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traceId

traceId : Show b => b -> b traceId a prints a and returns a, for debugging purposes. The default configuration on the participant logs these messages at DEBUG level.

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debug

debug : (Show b, Action m) => b -> m () debug x prints x for debugging purposes. The default configuration on the participant logs these messages at DEBUG level.

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debugRaw

debugRaw : Action m => Text -> m () debugRaw msg prints msg for debugging purposes. The default configuration on the participant logs these messages at DEBUG level.

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fst

fst : (a, b) -> a Return the first element of a tuple.

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snd

snd : (a, b) -> b Return the second element of a tuple.

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truncate

truncate : Numeric n -> Int truncate x rounds x toward zero.

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intToNumeric

intToNumeric : NumericScale n => Int -> Numeric n Convert an Int to a Numeric.

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intToDecimal

intToDecimal : Int -> Decimal Convert an Int to a Decimal.

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roundBankers

roundBankers : Int -> Numeric n -> Numeric n Bankers’ Rounding: roundBankers dp x rounds x to dp decimal places, where a .5 is rounded to the nearest even digit.

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roundCommercial

roundCommercial : NumericScale n => Int -> Numeric n -> Numeric n Commercial Rounding: roundCommercial dp x rounds x to dp decimal places, where a .5 is rounded away from zero.

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round

round : NumericScale n => Numeric n -> Int Round a Numeric to the nearest integer, where a .5 is rounded away from zero.

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floor

floor : NumericScale n => Numeric n -> Int Round a Decimal down to the nearest integer.

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ceiling

ceiling : NumericScale n => Numeric n -> Int Round a Decimal up to the nearest integer.

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null

null : [a] -> Bool Is the list empty? null xs is true if xs is the empty list.

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filter

filter : (a -> Bool) -> [a] -> [a] Filters the list using the function: keep only the elements where the predicate holds.

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sum

sum : Additive a => [a] -> a Add together all the elements in the list.

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product

product : Multiplicative a => [a] -> a Multiply all the elements in the list together.

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undefined

undefined : a A convenience function that can be used to mark something not implemented. Always throws an error with “Not implemented.”

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softFetch

softFetch : HasSoftFetch t => ContractId t -> Update t

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softExercise

softExercise : HasSoftExercise t c r => ContractId t -> c -> Update r

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stakeholder

stakeholder : (HasSignatory t, HasObserver t) => t -> [Party] The stakeholders of a contract: its signatories and observers.

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maintainer

maintainer : HasMaintainer t k => k -> [Party] The list of maintainers of a contract key.

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lookupByKey

lookupByKey : (HasKey t k, HasLookupNByKey t k) => k -> Update (Optional (ContractId t)) Look up the contract ID t associated with a given contract key k (see lookupNByKey for more on contract order). You must pass the t using an explicit type application. For instance, if you want to look up a contract of template Account by its key k, you must call lookupByKey @Account k.

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fetchByKey

fetchByKey : HasFetchByKey t k => k -> Update (ContractId t, t) Fetch the first contract ID and contract data associated with the given contract key (see lookupNByKey for more on contract order). You must pass the t using an explicit type application. For instance, if you want to fetch a contract of template Account by its key k, you must call fetchByKey @Account k.

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exerciseByKey

exerciseByKey : HasExerciseByKey t k c r => k -> c -> Update r Exercise a choice on the first contract associated with the given key (see lookupNByKey for more on contract order). You must pass the t using an explicit type application. For instance, if you want to exercise a choice Withdraw on a contract of template Account given by its key k, you must call exerciseByKey @Account k Withdraw.

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createAndExercise

createAndExercise : (HasCreate t, HasExercise t c r) => t -> c -> Update r Create a contract and exercise the choice on the newly created contract.

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templateTypeRep

templateTypeRep : HasTemplateTypeRep t => TemplateTypeRep Generate a unique textual representation of the template id.

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toAnyTemplate

toAnyTemplate : HasToAnyTemplate t => t -> AnyTemplate Wrap the template in AnyTemplate. Only available for Daml-LF 1.7 or later.

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fromAnyTemplate

fromAnyTemplate : HasFromAnyTemplate t => AnyTemplate -> Optional t Extract the underlying template from AnyTemplate if the type matches or return None. Only available for Daml-LF 1.7 or later.

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toAnyChoice

toAnyChoice : (HasTemplateTypeRep t, HasToAnyChoice t c r) => c -> AnyChoice Wrap a choice in AnyChoice. You must pass the template type t using an explicit type application. For example toAnyChoice @Account Withdraw. Only available for Daml-LF 1.7 or later.

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fromAnyChoice

fromAnyChoice : (HasTemplateTypeRep t, HasFromAnyChoice t c r) => AnyChoice -> Optional c Extract the underlying choice from AnyChoice if the template and choice types match, or return None. You must pass the template type t using an explicit type application. For example fromAnyChoice @Account choice. Only available for Daml-LF 1.7 or later.

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visibleByKey

visibleByKey : (HasKey t k, HasLookupNByKey t k) => k -> Update Bool True if contract exists, submitter is a stakeholder, and all maintainers authorize. False if contract does not exist and all maintainers authorize. Fails otherwise.

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otherwise

otherwise : Bool Used as an alternative in conditions.

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map

map : (a -> b) -> [a] -> [b] map f xs applies the function f to all elements of the list xs and returns the list of results (in the same order as xs).

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foldr

foldr : (a -> b -> b) -> b -> [a] -> b This function is a right fold, which you can use to manipulate lists. foldr f i xs performs a right fold over the list xs using the function f, using the starting value i. Note that foldr works from right-to-left over the list elements.

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.

. : (b -> c) -> (a -> b) -> a -> c Composes two functions, i.e., (f . g) x = f (g x).

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const

const : a -> b -> a const x is a unary function which evaluates to x for all inputs.

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$

$ : (a -> b) -> a -> b Take a function from a to b and a value of type a, and apply the function to the value of type a, returning a value of type b. This function has a very low precedence, which is why you might want to use it instead of regular function application.

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&&

&& : Bool -> Bool -> Bool Boolean “and”. This function has short-circuiting semantics, i.e., when both arguments are present and the first arguments evaluates to ‘False’, the second argument is not evaluated at all.

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||

|| : Bool -> Bool -> Bool Boolean “or”. This function has short-circuiting semantics, i.e., when both arguments are present and the first arguments evaluates to ‘True’, the second argument is not evaluated at all.

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not

not : Bool -> Bool Boolean “not”

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error

error : Text -> a Throws a GeneralError exception.

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subtract

subtract : Additive a => a -> a -> a subtract x y is equivalent to y - x. This is useful for partial application, e.g., in subtract 1 since (- 1) is interpreted as the number -1 and not a function that subtracts 1 from its argument.

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modulo

% : Int -> Int -> Int x % y calculates the remainder of x by y

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shows

shows : Show a => a -> ShowS

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showParen

showParen : Bool -> ShowS -> ShowS Utility function that surrounds the inner show function with parentheses when the ‘Bool’ parameter is ‘True’.

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showString

showString : Text -> ShowS Utility function converting a ‘String’ to a show function that simply prepends the string unchanged.

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showSpace

showSpace : ShowS Prepends a single space to the front of the string.

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showCommaSpace

showCommaSpace : ShowS Prepends a comma and a single space to the front of the string.

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Orphan Typeclass Instances