Updated syntax tree to support variables in the espression.

parser.py

@@ -34,6 +34,7 @@ class Parser:
 	def __init__(self, tokens):
 		if len(tokens) == 0:
 			raise ValueError("Token list can't be empty")
+		self.variables = {}
 		self.tokens = tokens
 		self.current_token = None
 		self.advance_current_token()
@@ -51,6 +52,7 @@ class Parser:
 			return node
 		elif self.current_token.type == token.TokenType.variable:
 			node = Variable(self.current_token)
+			self.variables[self.current_token.value] = node
 			self.advance_current_token()
 			return node
 		elif self.current_token.type == token.TokenType.exp_start:
@@ -91,3 +93,26 @@ class Parser:
 		
 	def generate_ast(self):
 		return self.topLevel()
+		
+	def update_variable(self, symbol, value):
+		if symbol in self.variables:
+			self.variables[symbol].value = float(value)
+		else:
+			raise ValueError("Variable value must be a number.", value)
+			
+	def update_variables(self, variables):
+		if len(variables) == 0:
+			return
+			
+		for symbol in variables:
+			if symbol in self.variables:
+				self.variables[symbol].value = float(variables[symbol])
+			else:
+				raise ValueError("Variable value must be a number.")
+				
+	def get_variable_value_pairs(self):
+		keys = {}
+		
+		for symbol in self.variables:
+			keys[symbol] = self.variables[symbol].value
+		return keys