Very early work in adopting new parser for actual execution of commands.
Not turned on yet.
Factor execution aspects from parser_t to parse_execution_context_t .
Still searching for best way to use new parser for execution.
New ideas about how to use new parser for execution. Beginnings of
implementation.
Cleanup thrashing around in parser_t. New parser execution lives in
parse_execution.cpp
Facilities for turning on new AST-based parser.
Fix a few errors identified by testing new parser