say I am parsing a message in this format:
2-byte message length + 2-byte instruction code + message body, where the 2-byte instruction code is a predefined set of constants, e.g. 0x01, 0x01234 etc.
I could use this parser:
short_>>short_>>*char_. and resort to the attributes of short_in a post-check to check whether the instruction code is legal or not .
what if I want to embed the legal instruction code set in the parser itself, and determine whether this is a legal message at one go? .i.e. short_>>(what to put here)>>*char?

Thanks.