Tuple

Tuples are inductive types (see chapter Inductive Classes for details). The module core defines the tuple type in the following manner.

B: ANY

class
    TUPLE[A,B]
create
    tuple(first:A, second:B)
end

Since tuples are used frequently there are some shorthands. (A,B) is a shorthand for TUPLE[A,B] and (a,b) is a shorthand for tuple(a,b).

(A,B,C) is parsed as (A,(B,C)) and (a,b,c) is parsed as (a,(b,c)).

There are the functions first and second to extract the first and the second element of a tuple.

first(t:(A,B)): A
        -- The first element of the tuple 't'.
    -> inspect
           t
       case (a,_) then
           a

second(t:(A,B)): A
        -- The second element of the tuple 't'.
    -> inspect
           t
       case (_,b) then
           b

Since the type TUPLE has only one constructor the inspect expressions for pattern matching need only one case.

The compiler adds an equality function and an inheritance from ANY for all inductive types automatically.

In order to access elements of n-ary tuples, the first and second functions have to be applied iteratively. Examples:

(a,b,c).first          =    a
(a,b,c).second         =    (b,c)
(a,b,c).second.first   =    b
(a,b,c).second.second  =    b

((a,b),c).first        =    (a,b)
((a,b),c).first.first  =    a
((a,b),c).first.second =    b
((a,b),c).second       =    c