program = _{ SOI ~ "\n"* ~ (stmt ~ "\n"+) * ~ stmt? ~ EOI }


stmt = { ((label ~ ":")? ~ instruction)}


instruction = {
    no_arg_instruction |
    arg_instruction ~ argument |
    jump_instruction ~ jump_argument |
    memory_location_instruction ~ memory_location |
    constant_arg_instruction ~ digit_literal
}

memory_location_instruction = {"STA"}
constant_arg_instruction = {"BRZ" | "BRC" | "BRN"}
jump_instruction = {"JMP"}
arg_instruction = {"LDA" | "ADD" | "SUB"}
no_arg_instruction = { "NOP" }

jump_argument = { jump_location | label}
argument = { memory_location | digit_literal }
memory_location = { "(" ~ ASCII_HEX_DIGIT ~")" }
digit_literal = {"#" ~ ASCII_HEX_DIGIT}
jump_location = { ASCII_HEX_DIGIT }

label = { ASCII_ALPHA_UPPER+ }

WHITESPACE = _{ " " | "\t" }
COMMENT = _{"//" ~ (!"\n" ~ ANY)* }