langcc

The README is a work in progress, but some of these answers can be found in the documentation (https://arxiv.org/abs/2209.08385). In particular: > How are the error messages? langcc produces "confusing input pairs" for LR conflicts, which enable the user to pinpoint the cause of the error much more easily than the opaque shift/reduce errors in tools such as yacc/bison. > Does it produce source spans for intermediate AST nodes? Yes! You can find an example in https://github.com/jzimmerman/langcc/blob/main/examples/calc.... > Can it handle operator precedence without encoding the precedence into the grammar? Yes - detailed in the documentation. > Can it handle source-code-defined operator precedence? Depends on what you mean by source-code-defined. The operations supported by langcc's precedence stanzas (detailed in the documentation) are q

The language of BNF for langcc (https://github.com/jzimmerman/langcc/blob/main/grammars/meta...) provides many syntactic conveniences that are not present in a Lisp-like language, so the fact that langcc supports it is a nontrivial achievement. In particular, an LR(0) parser would not be anywhere near adequate for it.

> I suggest the developer also look into auto-generated visitor / traversal functions as well In fact, langcc already has visitor/traversal functions, though they are not so well documented yet. I have just added an example (expr_simpl in https://github.com/jzimmerman/langcc/blob/main/examples/calc...). > Another suggestion is to make sure the grammar preserves source information (file, line, column span) This is already present as well (the calc example illustrates this functionality). > implement re-printing which preserves comments and whitespace I considered doing this, but it's surprisingly difficult to get the specification right, especially in whitespace-sensitive languages like Python.