simple php define in drupal template - php

Question

I have next to no experience with php as a language, and am running it a little problem in producing a Drupal theme. What I need is to execute a function once, that will return a Boolean, then use that Boolean throughout the template.
Here is what I have so far:
html.tpl.php->
<?php
function testMobile(){
return false;
}
define('isMobile', testMobile());
?>
...
<?php
if(!isMobile){
echo '<h1>NOT MOBILE</h1>';
}else{
echo '<h1>IS MOBILE</h1>';
}
?>
page.tpl.php->
<?php
if(!isMobile){
echo '<h1>IS DESKTOP</h1>';
}else{
echo '<h1>NOT DESKTOP</h1>';
}
?>
In the drupal output I get this ->
NOT MOBILE
NOT DESKTOP
along with this error message:
Notice: Use of undefined constant isMobile - assumed 'isMobile' in include() (line 77 of /Users/#/#/#/sites/all/themes/#/templates/page.tpl.php).
what am I doing wrong here? How can I most easily achieve my goal?

Answer 1

It seems that the defined variable is falling out of the scope of the template file. You can simply solve this by using a session variable.
Below is a code sample ...
session_start(); // not necessary with drupal
$_SESSION['isMobile'] = testMobile();
function testMobile(){
return false;
}
In your template you can add following...
<?php
if(!$_SESSION['isMobile']){
echo '<h1>IS DESKTOP</h1>';
}else{
echo '<h1>NOT DESKTOP</h1>';
}
?>

Answer 2

Try to define variable in template.php in hook_theme_preprocess_page(&$vars, $hook).
So template.php can looks follow way:
function testMobile(){
return false;
}
function YOURTHEME_theme_preprocess_page(&$vars, $hook) {
$vars['isMobile'] = testMobile();
}
And page.tpl.php
<?php
if(!$isMobile){
echo '<h1>IS DESKTOP</h1>';
}else{
echo '<h1>NOT DESKTOP</h1>';
}
?>