Editing K (programming language) (section)

== Examples ==
K is an interpreted language where every statement is evaluated and its results displayed immediately. Literal expressions such as strings evaluate to themselves. Consequently, the [["Hello, World!" program|Hello world]]-program is trivial:
<pre>
"Hello world!"
</pre>
The following expression sorts a list of strings by their lengths:
<syntaxhighlight lang="k">
x@>#:'x
</syntaxhighlight>
The expression is evaluated from right to left as follows:
# #:'x returns the length of each word in the list x.
# > returns the indices that would sort a list of values in descending order.
# @ uses 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:
<syntaxhighlight lang="k">
{&/x!/:2_!x}
</syntaxhighlight>
The function is evaluated from right to left:
# !x enumerate the positive integers less than x.
# 2_ drops the first two elements of the enumeration (0 and 1).
# x!/: performs modulo division between the original integer and each value in the truncated list.
# &/ 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:
<syntaxhighlight lang="k">
2_&{&/x!/:2_!x}'!R
</syntaxhighlight>
The expression is evaluated from right to left
# !R enumerate the integers less than R.
# ' 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.
# & return the indices of the list where the value is 1.
# 2_ drop the first two elements of the enumeration (0 and 1)