JJIK is a LR(1) parser generator similar to YACC.

JJIK generates Rust code for parsing the language you specify using a GG file. Here is an example of a GG file for specifying simple arithmetic expressions:

%TERMINALS
Number("\d\d*")
Plus("+")
Star("\*")
LeftParen("\(")
RightParen("\)")

%RULES
E = E Plus E
| E Star E
| LeftParen E RightParen
| Number;

%PRIORITIES
E(2)
Star
E(1)
Plus

GG file does not allow actions to be embedded into the grammar. Instead, JJIK generates a parser module with a parse method that returns a concrete syntax tree representation of your input. You can then insert your actions during tree traversal.

All information on how to use JJIK, the syntax for specifying a grammar using GG, and how to traverse the returned concrete syntax tree can be read in the crate's documentation.

Moreover, you can check out an example project utilizing JJIK for parsing mathematical expressions here.

Unlike some parser generators out there, JJIK does not accept actions in the grammar specification. The main reasons are to keep Rust code out of the GG file and to keep things simple. The drawback of this approach is having the concrete syntax tree explicitly constructed, which might be wasteful, compared to, for example, directly constructing the abstract syntax tree, or evaluating expressions.

If there are any errors encountered during lexing or parsing, the parser function will return an Result::Err(String) which explicitly show where the error occured, and in case of syntax error, the list of expected tokens. For example, if the string "100 * 200 500" is given as input to jjik_simple_calculator::calculate, it will return the following error:

Line   1|100 * 200 500
                   ^--
error: found Number, expected: [End, Plus, Minus, Star, Slash]

JJIK is pronounced like the Indonesian word jijik which means "disgusting" and I usually pronounce the well known parser generator, YACC, as "yuck", a word used to express disgust :)