manual.md

Command

If you run yaccgo , it will show as follow:

Understandable yacc generator , it can generate go/js/rust code

Usage:
  yaccgo [command]

Available Commands:
  completion  generate the autocompletion script for the specified shell
  debug       open debug mode
  generate    generate filetype input.y output.go
  help        Help about any command

Flags:
  -h, --help   help for yaccgo

Use "yaccgo [command] --help" for more information about a command.

It has sub command like generate, debug, help

sub command

generate

The command use as follow:

yaccgo generate {filetype} {inputfile} {outputfile} 

filetype it has go typescript, and rust will support in feature.

example:

yaccgo generate go examples/expr.y examples/e.go

it will generate golang file in examples/e.go , and the input file is examples/expr.y, file type is go

example

yaccgo generate typescript examples/exprts.y examples/e.ts

It will create a typescript file in examples/e.ts, input file is examples/exprts.y

Debug

command format as follow:

yaccgo debug {inputfile}

it will generate yacc debug information.

grammar file specification

grammar file is '.y' as postfix files, use as input file for yaccgo. examples/expr.y and examples/exprts.y above is grammar files

Sections

grammar file consists of the following sections:

• Declarations
• Rules
• Programs

and sections are seperated by %% each other, so a complete grammar file is like this:

Declarations
%%
Rules
%%
Programs

Declarations

they are consist of like that:

%{
Import codes
const variables define
global variables define
other header codes
%}
start define
sematics value type define
terminal symbol define
precedence define

all parts will persent as follow:

• header codes

header codes are wrap by %{ %},Usually they contain import codes, const defines , global variables define and so on.

example

%{
  
  package main
  
  import (

  	"fmt"

  )
  
  %}

• start define

start define specify nonterminal symbol start in grammar.

%start nonterminal

example

%start E

indicate E is the start symbol in grammar.

• sematics value type define

Every terminal symbol or nonterminal symbol has a sematics value type, use %union to define the value type,
use %token to specify a value type to terminal symbol, or use %type to specify a value type to nonterminal symbol.

%token's form is:

%token <tag> name

%type's form is:

%type <tag> name

%union form is:

%union {
		XXX
	}

examples

%union {
    //it is go code form
		val int
	}
	
%type	<val>	E
%token	<val>	NUM

• terminal symbol define

define symbol is terminal symbol, the forms are:

%token name
%token name interger-value

if %token is not following with interger-value, the system specify identification number automatically, or following with interger-value, specify identification number by user.

• precedence define

  Precedence is a method to resolve shift/reduce conflict. for example, if the rule is

  ...
  %%
  expr	   : expr '=' expr    
         	| expr '+' expr 
         	| expr '-' expr 
         	| expr '*' expr 
           | expr '/' expr 
         	| NAME 
         	
  

  When expr + expr ,and next symbol is '*', Parser do not know should shift symbol '*' , or reduce expr + expr to expr . this grammar is ambiguous, but you do not need to rewrite the grammar, just use precedence can resolve the confict.precedence has keywords: %left, %right, %nonassoc or %precedence , followed by tokens.

  Thus:

  %left '+' '-' 
  %left '*' '/'
  

  in define above, '+', '-' is left associative, and lower precedence than '*' and '/' . if the operators is not associative , use %nonassoc or %precedence

Rules

rules form is :

A : Body {Actions}

A represents a nonterminal symbol, Body represents a list of zero or more symbol,(containing terminal symbols or nonterminal symbols) .

rules (or production rules ) has three parts.

• Left part : At the beginning of the rule, such as A above, followed by:
• Body or Right part: after : , a list of symbols.
• Actions: after the Body，one or more statements enclosed in { and }. $ specify pseudo-variable for action operate the symbol sematics value. $$ represents the left part sematics value, $n( n is number starting from 1) specify the nth symbol's sematic value .

for examples

expr		   : expr '+' expr 
        	{ 
           		$$ = node( '+', $1, $3 ); 
         }

Programs

Other subroutines.