What am I missing??

Here is the code I have

{{#setVar "arrayCount" this.items.length}}

intended to set a variable using the helper

setVar: function(nName, vValue, options) {
    if (!options.data.root) {
        options.data.root = {};
    }
        options.data.root[nName] = vValue;
    }

and then comparing this value

{{#checkIf {{math {{@root.arrayCount}} '-' 1}} '==' @index}}

I get the error

Rendering process failed
An error occurred during rendering process:

Unexpected token ‘;’

I have been round and round on this – what am I doing wrong?

Cheers!!