If you pass array types as an argument to the PL/Tcl function, they are passed as a string value, along with the brackets and the commas. Let's take a look at an example:

CREATE OR REPLACE FUNCTION tcl_array_test(integer[]) RETURNS int
AS $$
    set length [string length $1]
    return $length
$$ LANGUAGE pltcl;

testdb=# select tcl_array_test(ARRAY[1,2,3]);
 tcl_array_test 
----------------
       7
    (1 row)

You are probably surprised at the return value of the preceding function. You passed an integer array to the function that is converted to a string value {1,2,3}, the length of which is indeed 7. If you want to process array values independently, you need a bit of string manipulation to extract the list out of the string, do the manipulation, and convert it back to the string format that you received it in.

Let's take a look at an example PL/Tcl function that will reverse an integer array and return the reversed integer array:

CREATE OR REPLACE FUNCTION tcl_reverse_array(integer[]) RETURNS integer[]
AS $$
  set lst [regexp -all -inline {[0-9]} $1]
  set lst [join [lreverse $lst] ","]
  set lst  "{$lst}"
  return $lst
$$ LANGUAGE pltcl;
postgres=# select tcl_reverse_array(ARRAY[1,2,3]);
 tcl_reverse_array 
-------------------
 {3,2,1}
(1 row)

The preceding function does the following: