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 defines how ASTs are to be generated. For example, in a grammar with E --> E + T a dependency between T and E can be declared so that only one AST type is generated for both.
  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.

Quick Example: JSON Parser

The following is a Rustlr grammar: ```

Rustlr Grammar for JSON

auto lifetime 'lt lexterminal LBRACE { lexterminal RBRACE } lexterminal LBRACK [ lexterminal RBRACK ] lexterminal LPAREN ( lexterminal RPAREN ) lexterminal COLON : lexterminal COMMA , lexterminal NULL null lexterminal MINUS - valueterminal TRUE~ bool~ Alphanum("true")~ true valueterminal FALSE~ bool~ Alphanum("false")~ false valueterminal STRING~ &'lt str~ Strlit(n)~ &n[1..n.len()-1] valueterminal NUM~ i64~ Num(n)~ n valueterminal FLOAT~ f64~ Float(n)~ n valueterminal BIGNUM~ &'lt str~ BigNumber(n)~ n nonterminal Integer i64 nonterminal Floatpt f64 nonterminal Boolean bool nonterminals Value KeyValuePair Number nonterminal List : Value nonterminal Object HashMap<&'lt str, LBox<@Value>>

startsymbol Value resync COMMA RBRACK RBRACE

Integer --> MINUS?:m NUM:n {if m.issome() {n*-1} else {n}} Floatpt --> MINUS?:m FLOAT:n {if m.issome() {-1.0*n} else {n}} Number:Bignum --> MINUS?:m BIGNUM Number:Int --> Integer Number:Float --> Floatpt Boolean --> TRUE | FALSE Value:Number --> Number Value:Boolean --> Boolean Value:Str --> STRING Value:Objectmap --> Object Value --> List Value --> NULL Value --> LPAREN Value RPAREN KeyValuePair --> STRING COLON Value List:List --> LBRACK Value RBRACK Object ==> LBRACE KeyValuePair:entries RBRACE { let mut kvmap = HashMap::new(); for (mut lbx) in entries { if let KeyValuePair(k,v) = lbx.take() { kvmap.insert(k,v); } } kvmap } <==

The following line is injected into json_ast.rs

$use std::collections::HashMap;

The following lines are injected into the parser

!mod jsonast; !fn main() { ! let srcfile = std::env::args().nth(1).unwrap(); ! let source = LexSource::new(&srcfile).unwrap(); ! let mut scanner1 = jsonlexer::fromsource(&source); ! 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 thelexterminalandvalueterminal` declarations. It also created most of the abstract syntax types and semantic actions required by the parser, alongside some manual overrides. As this is a quick example, we've also injected a main function, which expects the name of a json source as argument, directly into the parser. To run rustlr on this example,

  1. Install rustlr as a command-line application: cargo install rustlr
  2. Create a Cargo crate with rustlr = "0.4" in its dependencies
  3. save the grammar in the crate as json.grammar (must have .grammar suffix).
  4. Run rustlr with rustlr json.grammar -o src/main.rs
  5. call cargo run [some json file]

Note that <COMMA*> specifies a comma-separated list and normally generates semantic actions to create a vector. However, for JSON "objects" we chose to create a hashmap by manually writing the semantic action. Normally, Rustlr in auto mode generates an enum for each non-terminal symbol that's on the left-hand side of multiple productions, and a struct for non-terminals with a single production. However, declarations such as nonterminal List : Value allow a type to be absorbed into another: there is no separate type for List. There are other ways that a grammar can specify how ASTs are to be created, distinguishing the abstract syntax tree from the parse tree. Please consult the tutorial for further documentation.