A record is a collection of named fields:
val student = { name = "John Smith", wam = 90 }
> student : { name : String, wam : Int } = { name = "John Smith", wam = 90 }
student.name
> res0 : String = "John Smith"
Records are structurally typed:
{
def addAB(x : { a : Int, b : Int }) Int = x.a + x.b
val x = { c = "qwerty", b = 100, a = 42 }
addAB(x) // okay!
}
> 142
Records can be concatenated using the '&' operator:
val x = { a = 1, b = 2 }
val y = { c = "asdf" }
x & y
res1 : { a : Int, b : Int, c : String } = { a = 1, b = 2, c = "asdf" }
The operands of record concatenation must not have overlapping fields:
val x = { a = 1, b = 2 }
val y = { b = 3, c = "asdf" }
x & y
> 1:1:error: record concatenation has overlapping field(s) b
> x & y
> ^
Record types can also be concatenated:
type T = { a : Int, b : Int }
type U = { c : String }
T & U
> res2 : Type = { a : Int, b : Int, c : String }
A variant is a tagged union. A variant type specifies one or more fields, however a value of that type will only contain one of those fields.
type IntOrString = << IntValue : Int, StringValue : String >>
val x : IntOrString = << IntValue = 42 >>
val y : IntOrString = << StringValue = "qwerty" >>
Similar to records, variants are structurally typed.
A match expression can be used to identify which field of a variant value is valid:
def getIntOrElseZero(x : IntOrString) Int =
x match {
case IntValue(n) => n
case StringValue(_) => 0
}
The compiler will enforce that the cases of a match expression are exhaustive.
An example of a common use for variants is the Option type:
def Option(T : Type) Type = << Some : T, None : Unit >>
In fact, even the Boolean type in Cooma is a variant type:
type Boolean = << True : Unit, False : Unit >>
Vectors are a built-in ordered collection type:
[42, 100, 16]
> res3 : Vector(Int) = [42, 100, 16]
Built-in vector operations are available in the prelude:
val v = [42, 100, 16]
> v : Vector(Int) = [42, 100, 16]
Vectors.append(Int, v, 1)
> res4 : Vector(Int) = [42, 100, 16, 1]
Vectors.concat(Int, v, [1, 2, 3])
> res5 : Vector(Int) = [42, 100, 16, 1, 2, 3]
Vectors.get(Int, v, 2)
> res6 : Int = 16
Vectors.prepend(Int, v, 1)
> res7 : Vector(Int) = [1, 42, 100, 16]
Vectors.put(Int, v, 1, 7)
> res8 : Vector(Int) = [42, 7, 16]