// 1. Void manifests itself.
void

// 2. Iota - an intangible particle that can
//    be distinguished from void.
iota := not void

// 3. Boolean proposition is a iota of truthfulness.
bool := iota

true, false := bool

not x :=
    x := bool
    -> x ?
        true  -> false
        false -> true

x and y :=
    x, y := bool
    -> x ?
        true  -> y
        false -> false

x or y :=
    x, y := bool
    -> x ?
        true  -> true
        false -> y

x xor y :=
    x, y := bool
    -> (x or y) and not (x and y)

// 4. Int stands for a whole number.
int ::
    int < int -> bool
    int > int -> bool
    int <= int -> bool
    int >= int -> bool

    int + int -> int
    int - int -> int
    int * int -> int
    int / int -> int
    int ^ int -> int
    int % int -> int // mod

// 5. List is a sequence of propositions.
item list ::
    append! item to list -> item
    list length -> int
    list[int] -> item
    list[int:int] -> item list
    item in list -> bool

// 5. Real stands for a real number.
real ::
    real  < real -> bool
    real  > real -> bool
    real <= real -> bool
    real >= real -> bool

    real + real -> real
    real - real -> real
    real * real -> real
    real / real -> real
    real ^ real -> real

    rounded real -> real
    floored real -> real
    sqrt real -> real

// 6. Rune is a character.
//
//    For any text encoding, there always
//    will be a finite set of characters
//    it assumes. Therefore, it's safe
//    to say any rune can be expressed as
//    as integer.
//
//    Corresponding fact: UTF-8 codepoint
rune := int

// 7. String is a sequence of characters.
string := rune list