Recursive descent parser for Bash scripts.

Converts tokens from the Tokenizer into AST nodes.

Grammar Overview

The parser follows Bash's grammar from parse.y:

script       → statement_list EOF
statement    → simple_command
             | compound_command
             | pipeline
             | control_flow
pipeline     → command ('|' command)*
command      → simple_command redirect*
simple_cmd   → assignment* name word* redirect*
compound_cmd → '{' list '}'
             | '(' list ')'
             | if_clause
             | for_clause
             | while_clause
             | case_clause
             | function_def