AAAAAAAAAAAAAA!!!!

From Esolang

AAAAAAAAAAAAAA!!!! is an esoteric programming language by User:Zzo38 which consists entirely of the letter A, spaces, commas, and exclamation points. If you type a line beginning with @ it can be a comment and contains anything, but it must be removed from the program before the interpreter can use it. If you type a newline it can count as a space, and multiple consecutive spaces or exclamation points can count as a single one.

Commands:

AA AAA n! Outputs number as a character
AAA AAAA AA n! Input a character store to index n
AAA AA n! Go to label n
AAAAA n! Define a label n
AAA AAAA AAA n! Skip n commands
AAAA AA n! Shift indexes n backwards
AAAA AAAA n! Shift indexes n forwards
AA AAAA AA! End program
AAA A AAA n! Begin define subroutine named n
AAAA A AAA! End define subroutine
AAA A AA AAAA n! End subroutine, return value n
AAAAAA n! Call subroutine n
AAAA, AAAA n! Forget n entries from subroutine stack
AAAA AAA n! Increment value at index n
AAAA AAA, n! Decrement value at index n unless value is zero
AAAA, A n! Set command change register to n
AAAA, AA A n! Change all commands in program that start with what is in command change register to start with n instead
AAAA, AA AAA n! Change all commands in program that end with what is in command change register to end with n instead
AAAAA, AA A n! Change all commands in program that start with n to start with what is in command change register instead
AAAAA, AA AAA n! Change all commands in program that end with n to end with what is in command change register instead
AAAAA, AAAAA! Clear command change register
AAAAA, AAAA A n! Add block of n number of A's at end of command change register
AAAAA, AAAA AAA n! Add block of n number of A's and comma at end of command change register
(Any invalid command or operators when reached by program pointer, causes fatal error, and does not allow the output that the program already made to be used for any purpose except for debugging this program.)

Operators:

AAAA = number 0
AAA = number 1
A = number 2
AA A = number 3
AAAA A = last index number read by a previous command
AAAAA, n = value at index n
AA A, a b = a+b
AA AA, a b = abs(a-b)
AAA, a b = a*b
AA AAA, a b = a AND b
AAAA, a b = a XOR b
AAAAAA n, a b = Call subroutine n with parameter a and b, and return value
AAAAA A n, a = Call subroutine n with parameter a and a, and return value
AAAAA AA = First parameter
AAAAA AAA = Second parameter

Example (copy input to output, forever):

AAAAA A! AAA AAAA AA A! AA AAA AAAAA, A! AAA AA A! AA AAAA AA!

Example (output "He"):

AA AAA AA AA, AAA, AAA, AA A AAA, AA A AA A AA A AAA, AA A AA A!
AA AAA AA A, AAA AAAAA A AAAA, AAA!
AA AAAA AA! AAA A AAA AAAA! AAA A AA AAAA AAA, AA A, AAA AAA, AA A AA A AA A,
AAA AAA, AA A AA A! AAAA A AAA!