ANTLR v4 Wish list

Analysis

• Reimplement grammar analysis engine
• Hush codes

Parsing

• Left recursion elimination and expression grammar simplification [ANTLR4:DONE]
• Scannerless parsing
• Error alternatives
• Maybe ambiguous alt parsing, yielding parse forest
• Improve tree pattern matching, rewrites; e.g., <"0":primary>
• syntactic predicates ala PEGs; needed in token rules. ~ and ! are taken at the moment. perhaps the negate operator '-LetterOrDigit'; might as well at the positive version also: &LetterOrDigit.

Lexing

• DFA-based / NFA-based Lexers
• Lexer modes
• Long int based tokens instead of objects; use token adaptor
• Unbuffered I/O

Templates

• Generate code that uses ST v4 [ANTLR4:DONE]
• Make default output=template action for single rule ref to be that rule's return value then perhaps $text for more complicated alts w/o -> actions.

Actions

• Allow $FIRST, $FOLLOW, $LOOK

Runtime

• Improve error messages when backtracking or using arbitrary lookahead
• Add Jim Idle's sync rule concept
• Make a real interpreter using NFA; allow access as library from Java code
• Tokens and Trees should both know their start/stop line, start/stop char position to make IDEs easier.
• Tree parser error handling should skip subtrees not nodes; these are programming errors not input errors. The flat stream makes it hard to resync.

Miscellaneous

• Default rule parameter values, same for scope fields.

Implementation

• Use ST v4 to generate code [ANTLR4:DONE]
• Create new code generation mechanism

Tools

• new gUnit
• Widgets
  • AST viewer
  • generate syntax aware editor from ANTLR grammar
  • parse tree viewer