How to use `$@$` as input operator of iterator(e.g. map)?

[fdtsaid]

Some predefined operator can be used as input operator of iterator. Such as the following example 

 

function test(a,b: int8 ^ 3) returns (c: int8 ^ 3)

  c = (map $+$ << 3 >>) (a, b); 

 

But I am trying to figure out how to use $@$ as input operator correctly. In the following program:  

 

function mapOp(arr1,arr2: int8 ^ 2 ^ 3) returns (oarr: int8 ^ 4 ^ 3)

let

  oarr = (map $@$ <<3>>) (arr1,arr2);

tel 

 

The intention of the above program is to concatenate each element of type int8^2 in arr1 and arr2 to value of type int8^4. But I got the following error:

Prefix operator $@$ expects 2 size parameters but is here used with 0

 

How to use $@$ as input operator of iterator in a correct way?