The parser copies the body of functions and aliases (and heredocs, duh) into memory and interprets it from there. This is necessary because otherwise a function

The parser copies the body of functions and aliases (and heredocs, duh) into memory and interprets it from there. This is necessary because otherwise a function that is called frequently would translate into a lot of system calls for file I/O. Also bash has to work with streams that are not seekable, like piped command output, and so it allows declarations that can be parsed and then later referred to in one pass.