_test.styl

/* Foo */
.hello
  width: 10px

  /*
Bar
  */
  &:after
    height: 30px /* Baz */

parse-stylus.js

var fs = require('fs');
var Parser = require('stylus').Parser;
var stylContent = fs.readFileSync('_test.styl', 'utf8');
var parser = new Parser(stylContent);
var ast = parser.parse();

console.log(require('util').inspect(ast, true, 100));

parsed.js

{ nodes: 
   [ { lineno: 1,
       column: 1,
       filename: undefined,
       str: '/* Foo */',
       suppress: true,
       inline: false },
     { lineno: 1,
       column: 10,
       filename: undefined,
       nodes: 
        [ { lineno: 2,
            column: 1,
            filename: undefined,
            inherits: true,
            segments: 
             [ { lineno: 2,
                 column: 1,
                 filename: undefined,
                 val: '.',
                 string: '.',
                 prefixed: false },
               { lineno: 2,
                 column: 2,
                 filename: undefined,
                 val: 'hello',
                 string: 'hello',
                 prefixed: false },
               [length]: 2 ],
            block: 
             { lineno: 2,
               column: 2,
               filename: undefined,
               nodes: 
                [ { lineno: 3,
                    column: 3,
                    filename: undefined,
                    segments: 
                     [ { lineno: 3,
                         column: 3,
                         filename: undefined,
                         name: 'width',
                         string: 'width',
                         val: null,
                         mixin: false },
                       [length]: 1 ],
                    expr: 
                     { lineno: 3,
                       column: 10,
                       filename: undefined,
                       nodes: 
                        [ { lineno: 3,
                            column: 10,
                            filename: undefined,
                            val: 10,
                            type: 'px',
                            raw: '10px' },
                          [length]: 1 ],
                       isList: undefined } },
                  { lineno: 5,
                    column: 3,
                    filename: undefined,
                    str: '/*\nBar\n  */',
                    suppress: true,
                    inline: false },
                  { lineno: 7,
                    column: 14,
                    filename: undefined,
                    nodes: 
                     [ { lineno: 8,
                         column: 3,
                         filename: undefined,
                         inherits: true,
                         segments: 
                          [ { lineno: 8,
                              column: 3,
                              filename: undefined,
                              val: '&',
                              string: '&',
                              prefixed: false },
                            { lineno: 8,
                              column: 4,
                              filename: undefined,
                              val: ':',
                              string: ':',
                              prefixed: false },
                            { lineno: 8,
                              column: 5,
                              filename: undefined,
                              val: 'after',
                              string: 'after',
                              prefixed: false },
                            [length]: 3 ],
                         block: 
                          { lineno: 8,
                            column: 5,
                            filename: undefined,
                            nodes: 
                             [ { lineno: 9,
                                 column: 5,
                                 filename: undefined,
                                 segments: 
                                  [ { lineno: 9,
                                      column: 5,
                                      filename: undefined,
                                      name: 'height',
                                      string: 'height',
                                      val: null,
                                      mixin: false },
                                    [length]: 1 ],
                                 expr: 
                                  { lineno: 9,
                                    column: 13,
                                    filename: undefined,
                                    nodes: 
                                     [ { lineno: 9,
                                         column: 13,
                                         filename: undefined,
                                         val: 30,
                                         type: 'px',
                                         raw: '30px ' },
                                       [length]: 1 ],
                                    isList: undefined } },
                               [length]: 1 ],
                            parent: [Circular],
                            node: [Circular],
                            scope: true } },
                       [length]: 1 ],
                    extends: [ [length]: 0 ] },
                  [length]: 3 ],
               parent: [Circular],
               node: [Circular],
               scope: true } },
          [length]: 1 ],
       extends: [ [length]: 0 ] },
     [length]: 2 ] }