Prim
The Prim module is embedded in the PureScript compiler in order to provide compiler support for certain types — for example, value literals, or syntax sugar. It is implicitly imported unqualified in every module except those that list it as a qualified import.
Prim does not include additional built-in types and kinds that are defined deeper in the compiler such as Type wildcards (e.g. f :: _ -> Int) and Quantified Types. Rather, these are documented in the PureScript language reference.
#Function
data Function :: Type -> Type -> TypeA function, which takes values of the type specified by the first type parameter, and returns values of the type specified by the second. In the JavaScript backend, this is a standard JavaScript Function.
The type constructor (->) is syntactic sugar for this type constructor.
It is recommended to use (->) rather than Function, where possible.
That is, prefer this:
f :: Number -> Number
to either of these:
f :: Function Number Number
f :: (->) Number Number
#Array
data Array :: Type -> TypeAn Array: a data structure supporting efficient random access. In the JavaScript backend, values of this type are represented as JavaScript Arrays at runtime.
Construct values using literals:
x = [1,2,3,4,5] :: Array Int
#Record
data Record :: Row Type -> TypeThe type of records whose fields are known at compile time. In the JavaScript backend, values of this type are represented as JavaScript Objects at runtime.
The type signature here means that the Record type constructor takes
a row of concrete types. For example:
type Person = Record (name :: String, age :: Number)
The syntactic sugar with curly braces { } is generally preferred, though:
type Person = { name :: String, age :: Number }
The row associates a type to each label which appears in the record.
Technical note: PureScript allows duplicate labels in rows, and the
meaning of Record r is based on the first occurrence of each label in
the row r.
#Number
data Number :: TypeA double precision floating point number (IEEE 754).
Construct values of this type with literals. Negative literals must be wrapped in parentheses if the negation sign could be mistaken for an infix operator:
x = 35.23 :: Number
y = -1.224e6 :: Number
z = exp (-1.0) :: Number
#Int
data Int :: TypeA 32-bit signed integer. See the purescript-integers package for details
of how this is accomplished when compiling to JavaScript.
Construct values of this type with literals. Hexadecimal syntax is supported. Negative literals must be wrapped in parentheses if the negation sign could be mistaken for an infix operator:
x = -23 :: Int
y = 0x17 :: Int
z = complement (-24) :: Int
Integers used as types are considered to have kind Int.
Unlike value-level Ints, which must be representable as a 32-bit signed integer,
type-level Ints are unbounded. Hexadecimal support is also supported at the type level.
type One :: Int
type One = 1
type Beyond32BitSignedInt :: Int
type Beyond32BitSignedInt = 2147483648
type HexInt :: Int
type HexInt = 0x17
Negative integer literals at the type level must be wrapped in parentheses if the negation sign could be mistaken for an infix operator.
type NegativeOne = -1
foo :: Proxy (-1) -> ...
#String
data String :: TypeA String. As in JavaScript, String values represent sequences of UTF-16 code units, which are not required to form a valid encoding of Unicode text (for example, lone surrogates are permitted).
Construct values of this type with literals, using double quotes ":
x = "hello, world" :: String
Multi-line string literals are also supported with triple quotes ("""):
x = """multi
line"""
At the type level, string literals represent types with kind Symbol.
These types will have kind String in a future release:
type Hello :: Symbol
type Hello = "Hello, world"
#Char
data Char :: TypeA single character (UTF-16 code unit). The JavaScript representation is a
normal String, which is guaranteed to contain one code unit. This means
that astral plane characters (i.e. those with code point values greater
than 0xFFFF) cannot be represented as Char values.
Construct values of this type with literals, using single quotes ':
x = 'a' :: Char
#Boolean
data Boolean :: TypeA JavaScript Boolean value.
Construct values of this type with the literals true and false.
The True and False types defined in Prim.Boolean have this type as their kind.
#Partial
class Partial The Partial type class is used to indicate that a function is partial, that is, it is not defined for all inputs. In practice, attempting to use a partial function with a bad input will usually cause an error to be thrown, although it is not safe to assume that this will happen in all cases. For more information, see purescript-partial.
#Type
data Type :: TypeType is the kind of all proper types: those that classify value-level terms.
For example the type Boolean has kind Type; denoted by Boolean :: Type.
#Constraint
data Constraint :: TypeConstraint is the kind of type class constraints.
For example, a type class declaration like this:
class Semigroup a where
append :: a -> a -> a
has the kind signature:
class Semigroup :: Type -> Constraint
#Symbol
data Symbol :: TypeSymbol is the kind of type-level strings.
Construct types of this kind using the same literal syntax as documented for strings.
type Hello :: Symbol
type Hello = "Hello, world"
#Row
data Row :: Type -> TypeRow is the kind constructor of label-indexed types which map type-level strings to other types.
The most common use of Row is Row Type, a row mapping labels to basic (of kind Type) types:
type ExampleRow :: Row Type
type ExampleRow = ( name :: String, values :: Array Int )
This is the kind of Row expected by the Record type constructor.
More advanced row kinds like Row (Type -> Type) are used much less frequently.