rustlr

LR-Style Parser Generator

A Tutorial with several examples is available.

Besides traditional LR and LALR parser generation, Rustlr supports the following options

  1. An experimental feature that generates parsers for Selective Marcus-Leermakers grammars. This is a larger class of unambiguous grammars than traditional LR and helps to allow new productions to be added to a grammar without creating conflicts (see the Appendix of the tutorial).
  2. The option of creating the abstract syntax data types and semantic actions from the grammar. Rustlr grammars contain a sub-language that controls how ASTs are to be generated.
  3. Support for choosing bumpalo to create recursive ASTs that use references instead of smart pointers: this enables deep pattern matching on recursive structures.
  4. Recognizes regex-style operators *, + and ?, which simplify the writing of grammars and allow better ASTs to be created.
  5. Generates a lexical scanner automatically from the grammar.
  6. Operator precedence and associativity declarations further allow grammars to be written that's closer to EBNF syntax.
  7. The ability to train the parser, interactively or from script, for better error reporting.
  8. Generates parsers for Rust and for F#. Rustlr is designed to promote typed functional programming languages in the creation of compilers and language-analysis tools. Parser generation for other such languages will gradually become available.

Rustlr aims to simplify the creation of precise and efficient parsers and will continue to evolve and incorporate new features, though backwards compatibility will be maintained as much as possible.

Quick Example: Arithmetic Expressions and Their Abstract Syntax

The following are the contents of a Rustlr grammar, simplecalc.grammar: ``` auto terminals + * - / ( ) # verbatim terminal symbols valterminal Int i32 # terminal symbol with value nonterminal E nonterminal T : E # specifies that AST for T should merge into E nonterminal F : E startsymbol E variant-group BinaryOp + - * / # simplifies AST enum by combining variants

production rules:

E --> E + T | E - T | T T --> T * F | T / F | F F:Neg --> - F # 'Neg' names enum variant in AST F --> Int | ( E )

!mod simplecalcast; // !-lines are injected verbatim into the parser !fn main() { ! let mut scanner1 = simplecalclexer::fromstr("10+-2*4"); ! let mut parser1 = makeparser(); ! let parseresult = parsewith(&mut parser1, &mut scanner1); ! let ast = ! parseresult. ! unwraporelse(|x| { ! println!("Parsing errors encountered; results not guaranteed.."); ! x ! }); ! println!("\nAST: {:?}\n",&ast); !}//main ```

In addition to a parser, the grammar generates a lexical scanner from the declarations of terminal symbols. It also created the following abstract syntax type and the semantic actions that produce instances of the type. ```

[derive(Debug)]

pub enum E { BinaryOp(&'static str,LBox,LBox), Int(i32), Neg(LBox), ENothing, } impl Default for E { fn default()->Self { E::ENothing } } `` The form of the AST type(s) was determined by additional declarations within the grammar. An enum is normally generated for each non-terminal with multiple productions, with a variant for each production. However, the enum variants generated from the productions forTandFare merged into the type forEby the declarations nonterminal T : Eandnonterminal F : E. Thevariant-group declaration combined what would-have-been four variants into one. The Neg` label on the unary minus rule separates that case from the "BinaryOp" variant group.

LBox is a custom smart pointer that automatically contains the line and column positions of the start of the AST construct in the original source. This information is usually required beyond the parsing stage.

Rustlr AST types implement the Default trait so that a partial result is always returned even when parse errors are encountered.

Automatically generated AST types and semantic actions can always be manually overridden.

Specifying operator precedence and associativity instead of using the T and F categories is also supported.

The generated parser and lexer normally form a separate module. However, as this is a quick example, we've injected a main directly into the parser file to demonstrate how to invoke the parser. To run this example,

  1. Install rustlr as a command-line application: cargo install rustlr
  2. Create a Cargo crate and cargo add rustlr inside the crate
  3. save the grammar in the crate as simplecalc.grammar. The filename determines the names of the modules created, and must have a .grammar suffix.
  4. Run rustlr in the crate with > rustlr simplecalc.grammar -o src/main.rs
  5. cargo run

The expected output is AST: BinaryOp("+", Int(10), BinaryOp("*", Neg(Int(2)), Int(4)))

New in Version 0.4.9: Conversion From Yacc/Bison Grammar.

Given a parser instance parser, it's now possible to call parser1.set_err_report(true), which will log parse errors internally instead of printing them to stderr. The error report can be retrieved by calling parser1.get_err_report().

New in Version 0.4.8: Conversion From Yacc/Bison Grammar.

If the rustlr executable is given a file path that ends in ".y", it will attempt to convert a yacc/bison style grammar into rustlr's own grammar syntax, stripping away all semantic actions and other language-specific content. All other command-line options are ignored.


Please consult the tutorial for further documentation.