K (programming Language) - Examples

Examples

K is an interpreted language where every statement is evaluated and its results immediately displayed. Literal expressions such as strings evaluate to themselves. Consequently, the Hello world-program is trivial:

"Hello world!"

The following expression sorts a list of strings by their lengths:

x@>#:'x

The expression is evaluated from right to left as follows:

1. #:'x returns the length of each word in the list x.
2. > returns the indices that would sort a list of values in descending order.
3. @ use the integer values on the right to index into the original list of strings.

A function to determine if a number is prime can be written as:

{&/x!/:2_!x}

The function is evaluated from right to left:

1. !x enumerate the positive integers less than x.
2. 2_ drops the first two elements of the enumeration (0 and 1).
3. x!/: performs modulo division between the original integer and each value in the truncated list.
4. &/ find the minimum value of the list of modulo result.

If x is not prime then one of the values returned by the modulo operation will be 0 and consequently the minimal value of the list. If x is prime then the minimal value will be 1, because x mod 2 is 1 for any prime greater than 2.

The function below can be used to list all of the prime numbers between 1 and R with:

(!R)@&{&/x!/:2_!x}'!R

The expression is evaluated from right to left

1. !R enumerate the integers less than R.
2. ' apply each value of the enumeration to the prime number function on the left. This will return a list of 0's and 1's.
3. & return the indices of the list where the value is 1.
4. @ use the integer values listed on the right to index into the list on the left.
5. (!R) A list of integers less than R.