Every value in Stone has an associated type.
You can get the type of a value by accessing its type property.
TODO: Any expression should allow a property access.
a := 123
a.type
#= Number.Integer
b := "abc"
b.type
#= Text
TRUE.type
#= Boolean
NULL.type
#= Null
c := 1.0
c.type
#= Number.Decimal
d := 1/2
d.type
#= Number.Rational
f := λ(x) { 2 * x }
f.type
#= Function
l := List(1, 2, 3)
l.type
#= List[Number.Integer]