Parsing and reflective printing, bidirectionally

Abstract

Language designers usually need to implement parsers and printers. Despite being two intimately related programs, in practice they are often designed separately, and then need to be revised and kept consistent as the language evolves. It will be more convenient if the parser and printer can be unified and developed in one single program, with their consistency guaranteed automatically. Furthermore, in certain scenarios (like showing compiler optimisation results to the programmer), it is desirable to have a more powerful reflective printer that, when an abstract syntax tree corresponding to a piece of program text is modified, can reflect the modification to the program text while preserving layouts, comments, and syntactic sugar. To address these needs, we propose a domain-specific language BIYACC, whose programs denote both a parser and a reflective printer for an unambiguous context-free grammar. BIYACC is based on the theory of bidirectional transformations, which helps to guarantee by construction that the pairs of parsers and reflective printers generated by BIYACC are consistent. We show that BIYACC is capable of facilitating many tasks such as Pombrio and Krishnamurthi's "resugaring", simple refactoring, and language evolution.

Unifying Parsing and Reflective Printing for Fully Disambiguated Grammars

“…• We proposed the notion of bi-filters, which enables BIYACC to disambiguate ambiguous grammars while still respecting the consistency properties. This is the main new contribution compared to the previous SLE'16 version [55].…”

InDubio: A Combinator Library to Disambiguate Ambiguous Grammars

“…Thus, we are optimizing HaGLR so that it uses a better parse-table representation, and we are also considering to use shared packed parse forests [24] and data structure free compilation [18], which both use sharing to reduce runtime and memory consumption. We are also integrating the disambiguation filters with BiYacc [25], a tool for generating both a parser and a reflective printer [27,26] for an unambiguous context-free grammar. The use of disambiguation filters can be helpful in extending this tool to also support ambiguous context-free grammars, therefore increasing its expressiveness and allowing for more test cases to be supported by this tool.…”

Expressing disambiguation filters as combinators

“…Thus we are refactoring HaGLR so that uses a better representation for parse-tables (which steer the parser at runtime), and we are also considering to use shared packed parse forests [13] which use sharing to reduce runtime and memory consumption. We are also integrating the disambiguation filters with BiYacc [15], a tool for generating both a parser and a reflective printer [16] for an unambiguous context-free grammar. The use of disambiguation filters can be helpful in extending this tool to also support ambiguous context-free grammars, therefore increasing its expressiveness and allowing for more test cases to be supported by this tool.…”