Tabitha Programming Guide

Addresses

In Tabitha, an address is what a C programmer might call a pointers. It is a value which identifies a location in memory where data is stored. Addresses are very useful for developing performant applications.

Declaring an Address

Since they have their own types, addresses can be declared just like any other variables.

Addr[Int] x
stacked Addr[Int] y 
heaped Addr[Int] z

The type Addr[Int] is one which belongs to variables representing the memory address of some integer. Similarly, Addr[Float] is for the address of a Float. We can create addresses for any type, including other addresses. For example if we were to make a declaration,

Addr[Addr[Int]] x

then this x would hold the memory address to data which corresponds to the address of an integer.

Getting an Address

Given a variable or subvalue thereof, we can get its address in memory using the locate operator ?.

Int x = 10 
Addr[Int] x_addr = x?

The variable x_addr should now hold the memory address of the variable x. We can do this with any referencable value in Tabitha. For example, we can do it with vector elements:

Vec[Int, 10] x
Addr[Int] elem_ptr = x[3]?

The variable elem_ptr holds the memory address where we find the elemnt of index 3 of vector x. This also wors with members of collections types.

collection type Point {
    Float x
    Float y
}

function foo {
    Point p 
    p.x = 10
    Addr[Float px_ptr = p.x?  
}

The variable px_ptr hold the memory address where we can find the value p.x, which happens to be 10-

Querying an Address

Given some address, we can get the value found at that address using the query operator @.

Int a = 10
Int b = 20 
Addr[Int] a_ptr = a? 
Addr[Int] b_ptr = b? 
Int c = @a_ptr + @b_ptr

Here, we have taken some extra steps in summing two varaibles, for the sake of demonstrationo. We have two variables a and b. We get their memory addresses and store them in a_ptr and b_ptr respectively. We then create a new variable c and assign it the sum of the integer values found at a_ptr and b_ptr. Now c should have the value 30.

It should be note that, as of yet, Tabitha does not support address arithmetic. That is, it does not allow one to add addresses together, or add numbers to addresses. This may be changed in the future.