The braces around an expression denote a function. Because this
function contains a single variable,
x, it is a monadic
function or a monad.
In the remainder of this page, a colored box, like the one below, indicates
code. Go ahead, click it! Then use the back button to return to
When running the above code, Klong will respond
indicating that the expression evaluated to a function of one
You can apply the function to a value, say 251, using the Apply
@) verb, e.g.:
Expressions evaluate from the right to the left, so the first thing the function does is 1 Divide 2, giving 0.5:
The next operation is x Power (1 Divide 2). x1/2 is the square root of x, so this part of the expression computes the square root of 251:
_) then floors (rounds toward −infinity)
that value. So
_x^1%2 is Floor (x Power (1 Divide 2)),
in this case the floor of the square root of 251.
!) creates a vector containing all integers
from zero up to, but not including, that value. In this case,
[0 ... 14] (a vector of the numbers
from 0 to 14).
A number plus a vector gives a new vector with the number added to each
of its elements, so
2+ adds 2 to each element from the
2+[0 ... 14] =
[2 ... 16].
!:\ is a combination of the verb
and the adverb
:\ (Each-Left). x Remainder-Each-Left
applies Remainder to each element of the previous step (
x as its left operand. It creates a new vector containing
[1 2 3 1 ...].
&/ is a combination of Min and Over. Min returns the
minimum of two numbers and Over folds Min over a vector, so Min-Over
returns the minimum of a vector:
In this case, the minimum of the vector is 1, because 1 is the smallest remainder obtained by dividing 251 by 2..16. In other words, 251 is prime.
If we had applied the function to a non-prime number, like 253, at least one of the elements of the vector would have divided that number with a remainder of 0, so the result of the function would also be 0. Let's see:
Of course, the prime function is sufficiently complex to bind it
to a name using Define (
You can then use the function application syntax to apply it to some values:
Of course, the
@ operator would also work:
prime function only works for values greater than
two. What will it return for 0, 1, and 2? Why?