Jison Demo

index.js

const {Parser} = require('jison');


const parser = new Parser(`
/* lexical grammar */
%lex
%%

\\s+                   /* skip whitespace */
"var"                    return 'VAR'
[a-zA-Z_$][a-zA-Z_$0-9]* return 'VAR_NAME'
"="                      return '='
[0-9]+                   return 'NUMBER'
<<EOF>>                  return 'EOF'
.                        return 'INVALID'

/lex

/* operator associations and precedence */

%start file

%% /* language grammar */

var_expression
    : VAR VAR_NAME "=" NUMBER
        {$$ = {type: "VarExp", "name": $2, "value": $4}}
    | VAR VAR_NAME
        {$$ = {type: "VarExp", "name": $2}};

set_expression
    : VAR_NAME "=" NUMBER
        {$$ = {type: "SetExp", "name": $1, "value": $3}};

expression
    : var_expression
        {$$ = $1}
    | set_expression
        {$$ = $1};

expression_list
    : expression
        {$$ = [$1];}
    | expression expression_list
        {$$ = [$1, ...$2];}
;

file
    : expression_list EOF
        {return $1;}
    ;
`);

const program = parser.parse(`
var x
var y = 4
z = 3
`);

console.log(program);

package.json

{
  "name": "jison-doodle",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "jison": "^0.4.18"
  }
}