rpn.php

Professional PHP5 code for this book

<?php
     
     require_once 'FSM.php';
     
     function BeginBuildNumber($symbol, $payload)
     {
         array_push($payload, $symbol);
     }
     
    function BuildNumber($symbol, $payload)
    {
        $n = array_pop($payload);
        $n = $n . $symbol;
        array_push($payload, $n);
    }
    
    function EndBuildNumber($symbol, $payload)
    {
        $n = array_pop($payload);
        array_push($payload, (int)$n);
    }
    
    function DoOperator($symbol, $payload)
    {
        $ar = array_pop($payload);
       $al = array_pop($payload);
    
        if ($symbol == '+') {
            array_push($payload, $al + $ar);
        } elseif ($symbol == '-') {
            array_push($payload, $al - $ar);
        } elseif ($symbol == '*') {
            array_push($payload, $al * $ar);
        } elseif ($symbol == '/') {
            array_push($payload, $al / $ar);
        }
   }
    
    function DoEqual($symbol, $payload)
    {
        echo array_pop($payload) . "\n";
    }
    
    function Error($symbol, $payload)
    {
        echo "This does not compute: $symbol\n";
    }
    
    $stack = array();
    
    $fsm = new FSM('INIT', $stack);
   $fsm->setDefaultTransition('INIT', 'Error');
    
    $fsm->addTransitionAny('INIT', 'INIT');
    $fsm->addTransition('=', 'INIT', 'INIT', 'DoEqual');
    $fsm->addTransitions(range(0,9), 'INIT', 'BUILDING_NUMBER', 'BeginBuildNumber');
    $fsm->addTransitions(range(0,9), 'BUILDING_NUMBER', 'BUILDING_NUMBER', 'BuildNumber');
    $fsm->addTransition(' ', 'BUILDING_NUMBER', 'INIT', 'EndBuildNumber');
    $fsm->addTransitions(array('+','-','*','/'), 'INIT', 'INIT', 'DoOperator');
    
    echo "Expression:\n";
    $stdin = fopen('php://stdin', 'r');
    $expression = rtrim(fgets($stdin));
    $symbols = preg_split('//', $expression, -1, PREG_SPLIT_NO_EMPTY);
    
    $fsm->processList($symbols);