tree.js

// usage: flusspferd tree.js grammar.peg inputfile

const peg = require( "PEG_generator" ),
      fs = require( "fs-base" ),
      system = require( "system" );

var grammar = fs.rawOpen( system.args[ 1 ], "r" ).readWhole(),
    input = fs.rawOpen( system.args[ 2 ], "r" ).readWhole(),
    names = eval( peg.generateParserThrowing( grammar ) ),
    root = names[ 0 ],
    tree = this[ root ]( input );

if ( !tree[ 0 ] ) throw "Parsing failed";

print( peg.showTree( tree[ 1 ], names ) );