This is an example function definition from the APL language. Any serious APL user would have had a special keyboard. The first line says that this begins a function named SORT that sorts the array X and returns the value R. R is computed within the function body. The i operator generates index arrays. Thus the first line of the function body sets R to an empty array.
Assignment is the left arrow.
The next line is particularly hard for the novice to understand. Now we know what each piece means, but this is not very helpful for reading what the statement means. You have to know that APL operations are performed right to left. This evaluates to 0 for false or 1 for true. So if X is an empty array, we get 1.