The proposed changes, particularly tail recursion, an if operator, and a zip operator in effect give you a functional language with immutable state. While you

The proposed changes, particularly tail recursion, an if operator, and a zip operator in effect give you a functional language with immutable state. While you can't "write" to the Turing tape as a side effect as the language is immutable, you can create a new "tape" from previous states which is a modified version of the old tape.