Copyright ã 1994 by Sean Luke

COWS
Array Library
COWS Version 1.3
Sean Luke
March 20, 1994

The COWS Array library provides arrays of any number of dimensions up to 256, and of any length whatsoever.

Arrays and COWS

Because COWS has only one data type (the string), there are some odd things about the Array Library which are important to know before using it.

First off, arrays must be manually allocated and freed in COWS, much like object instances must be manually allocated and freed in Objective-C.  This is because the only data that can be stored on the COWS stack is the string.  So arrays cannot be created and placed on the stack, then bumped off by the interpreter.  This means that you have to watch your allocation carefullyÐthere's no garbage collection in the Array Library, other than arrays getting wiped out when re-loading the library.

Second, arrays are "stored" as variables by placing a unique string in a variableÐa pointer to the array, as it were.  This string is in the format "array X", where X is an integer that increases with the number of arrays currently allocated.

Lastly, arrays are always arrays of strings.  But if you think about it, you can make arrays of arrays as well, if you manually allocated an array for each cell of a grandfather array and place the pointer to it in the grandfather's cell.

The Library

The Array Library consists of two objects:  the COWSArrayLibrary (the library itself), and the COWSArrayNode, (arrays stored in the library's hash table).  Remember to include both in your project if you're building an application with COWS inside.  But only connect the COWSArrayLibrary to your interpreter.

Creating an Array

You create arrays using the command:

(make-array dimensions+)

This returns a pointer to the array.  dimensions is one or more values that define the dimensions of an array.  For example, if you wanted to make a 4 x 3 x 2 array, you'd make it with

Þ	(make-array 4 3 2)

To store the array-pointer in a variable (important if you want to refer to the array later!), you'd do it like this (assuming the variable array-var had been allocated already):

Þ	(set array-var (make-array 4 3 2))

Setting a Value in an Array

You set a value in an array using the command:

(set-array pointer value coordinates+)

This returns value.  pointer is the pointer to the array (see above), coordinates are the dimensional coordinates in the array for the cell you wish to set, and value is the value you want to set the cell to. 

All arrays created with this library start counting at 1.  So coordinates for the example above could range as [1±4], [1±3], [1±2].  This is different from C!  In C, the range would be 0-3, 0-2, and 0-1.  

Continuing the example above, let's say you wanted to set position 2,3,1 of array-var to the string "hello", position 4,1,2 to the number 5, and 1,2,2 to the value of the variable val.  You'd set them like so:

Þ	(set-array array-var "hello" 2 3 1)
	(set-array array-var 5 4 1 2)
	(set-array array-var val 1 2 2)

Retrieving a Value in an Array

You get a value in an array using the command:

(array pointer coordinates+)

This returns the value of the cell of cordinate coordinates of the array pointed to by pointer.  Once again, coordinates' ranges start at 1.

If you wanted to, say, print the value of the array stored in array-var at the coordinates 4,1,2, you'd write:

Þ	(array array-var 4 1 2)

Freeing an Array

You can free an array with the command:

(free-array pointer)

This returns t.  The array pointed to by pointer is freed, if it exists. 

To free an array pointed to by array-var, you'd write:

Þ	(free array-var)

Determining an Array

If you're not sure if a pointer is pointing to a valid array, you can check with:

(array? pointer)

This returns t if the array is valid, f if not. 

To check an array pointed to by array-var, you'd write:

Þ	(array? array-var)

Array Function Names

In review, the function names are:

make-array		Creates an array with dimensions dimensions.  
				Returns a pointer to the array.
	(make-array dimensions+)

set-array			Sets array pointer at coordinates coordinates to value.
				Coordinates start at 1, not 0.  Returns value.
	(set-array pointer value coordinates+)

array			Returns the value of array pointer at coordinates coordinates.
				Coordinates start at 1, not 0.
	(array pointer coordinates+)

free-array		Frees array pointer.  Returns t.
	(free-array pointer)

array?			Returns t if pointer is a valid array, f otherwise.
	(array? pointer)