J function is not working

Question

I am a complete beginner to J. My first attempt at writing a function is something like the totient function. It takes an array, assumed to be i.num for some number, num. And then computes the number of elements coprime to the tally of the array.

If I do it manually like this:

numbers =: i.7 
#(1=( #numbers)+./numbers)#numbers

it works. The result is 6.

So I want to turn this into a general function.

Tot =: monad :'(1=( #x)+./x)#x'
Tot i.11

This fails and I get a value error for x. I don't know why.

Answer 1

The monad's variable should be y, not x:

Tot =: monad :'(1=( #y)+./y)#y'

x is the left argument of a dyad.