lrgen

lrgen is an LALR(1) parser generator written in Go and targeting Go.

The grammar file consists of three parts divided by the %% markers:

Prologue
%%
Definitions
%%
Rules

Prologue

Any Go code will be copied verbatim. You may want to include a package declaration and import some packages at the beginning of this.

Definitions

The following directives are supported

• %token [type] {identifier} -- define terminal symbols
• %left {identifier} %right {identifier} %nonassoc {identifier} -- define precedence and associativity
• %type type {identifier} -- specify type for nonterminal symbols
• %error code -- code to be executed on syntax error
• %base identifier|type -- specify the base type of the parser

Rules

identifier ':' {identifier} [code] { '|' {identifier} [code] } ';'

The identifier to the left of : is the lhs of the production, and the identifier list on the right is the rhs, with an optional semantic action attached. The rhs can be separated by | and must be terminated by ;.

Generated Parser

The generated parser will be called y.tab.go. To use the parser, create a yyParser object, and pass tokens to its ParseToken method. On the end of input, pass 0 to it.

Desciption file

A description file y.output will be generated. It contains the state machine description, and also reports all conflicts.