Global Variables

I'm trying to set up a system of triggers that change this global variable when you enter them. I'm using the global variable as a way to represent different states the player is in and a number of functions will look to the global variable to set the player's speed and eventually animations, environment, and a number of different things. I think I'm going about it all wrong because everything I've done so far results in the scripts getting random parse errors at the ends of statements or before comment lines. I can't figure out where these problems are originating because they just move around as I try to change different things. Here are the script files I've made for this purpose. I hope somebody can help me figure out what I'm doing wrong. I'm also not sure how to initialize my global variable. Wherever I put it in scripts or in datablocks I wind up just getting parse errors and it becomes unusable.

function potionA::onEnter( %this )
{
// If the player is in either a neutral or depressed state increase it into a (more) depressed state.
if ($potionState >= 0 < 3)
{
$potionState++;
}
// If the player is in a hyper-depressed state do nothing.
if ($potionState >= 3)
{
return;
}
// If the player is in a stimulated state bring him to the neutral state and then to a depressed state.
if ($potionState < 0)
{
$potionState = 1;
}
}

function potionB::OnEnter(%this)
{
// If the player is in a neutral state bring him to a stimulated state.
if ( $potionState = 0 )
{
$potionState - 2;
}
// If the player is in a stimulated state increase it.
if ( $potionState < 0 > -3 )
{
$potionState--;
}
// If the player is in a hyper-stimulated state do nothing.
if ( $potionState = -3 )
{
return;
}
// If the player is in a depressed state bring him to the neutral state and then to a depressed state.
if ( $potionState > 0 )
{
$potionState = -2
}
}

function PotionAEnd::OnEnter(%this)
{
// If the player is in a depressed state reduce it
if ( $potionState > 0)
{
$potionState--;
}
}

function PotionBEnd::OnEnter(%this)
{
//If the player is in a neutral or depressed state do nothing.
if ( $potionState >= 0 )
{
return;
}
//If the player is in a stimulated state decrease it.
if ( $potionState < 0 > -3)
{
$potionState++;
}
//If the player is in a hyper-stimulated state greatly decrease it.
if ($potionState = -3)
{
$potionState + 2;
}
}

function Player::PotionState(%this)
{
if ($potionState = 0)
{
player.runSpeed = 16;
}

if ($potionState = 1)
{
player.runSpeed = 12;
}

if ($potionState = 2)
{
player.runSpeed = 8;
}

if ($potionState = 3)
{
player.runSpeed = 4;
}

if ($potionState = -1)
{
player.runSpeed = 12;
}

if ($potionState = -2)
{
player.runSpeed = 24;
}

if ($potionState = -3)
{
player.runSpeed = 32;
}
}

Thanks a lot for any help you can provide. I'm new and I'm not trying to do anything that complicated, but that doesn't seem to help.