Add swap and pop operations and simplify code

constants.py

@@ -20,3 +20,6 @@ HEX = 'HEX'
 DEC = 'DEC'
 BIN = 'BIN'
 
+SWAP = 'SWAP'
+POP = 'POP'
+

interpreter.py

@@ -10,9 +10,14 @@ from constants import (
 	NUMBER, EOF,
 	PLUS, MINUS, MUL, DIV, POW, SQRT,
 	HEX, DEC, BIN,
+	SWAP, POP,
 )
 
 
+class InterpreterError(Exception):
+	pass
+
+
 class Interpreter:
 	def __init__(self):
 		self.stack = []
@@ -23,39 +28,20 @@ class Interpreter:
 		self.lexer = lexer
 		self.current_token = self.lexer.get_next_token()
 
-	def eat(self, type):
-		if self.current_token.type == type:
-			self.current_token = self.lexer.get_next_token()
-		else:
-			raise Exception('Wrong token eaten')
-
-	def get_from_stack(self, pop=True):
-		if pop:
-			value = self.stack.pop()
-		else:
-			value = self.stack[-1]
-
-		if type(value) is str:
-			return self.ariables[value]
-
-		return value
-
 	def evaluate_binary_operator(self, token):
 		if len(self.stack) < 2:
-			raise Exception('Needs at least 2 values on the stack')
+			raise InterpreterError('Needs at least 2 values on the stack')
 
-		right = self.get_from_stack()
-		left = self.get_from_stack()
+		right = self.stack.pop()
+		left = self.stack.pop()
 		self.stack.append(token.value(left, right))
-		self.eat(token.type)
 
 	def evaluate_unary_operator(self, token):
 		if len(self.stack) < 1:
-			raise Exception('Needs at least 1 value on the stack')
+			raise InterpreterError('Needs at least 1 value on the stack')
 
-		value = self.get_from_stack()
+		value = self.stack.pop()
 		self.stack.append(token.value(value))
-		self.eat(token.type)
 
 	def set_mode(self, token):
 		self.mode = token.type
@@ -63,21 +49,27 @@ class Interpreter:
 
 	def parse(self, lexer):
 		self.init_lexer(lexer)
-		token = self.current_token
 
-		while token.type is not EOF:
-			if token.type in (PLUS, MINUS, MUL, DIV, POW):
-				self.evaluate_binary_operator(token)
-			elif token.type in (SQRT):
-				self.evaluate_unary_operator(token)
-			elif token.type == NUMBER:
-				self.stack.append(token.value)
-				self.eat(NUMBER)
-			elif token.type in (HEX, DEC, BIN):
-				self.set_mode(token)
-				self.eat(token.type)
+		while self.current_token.type is not EOF:
+			if self.current_token.type == NUMBER:
+				self.stack.append(self.current_token.value)
+			elif self.current_token.type in (PLUS, MINUS, MUL, DIV, POW):
+				self.evaluate_binary_operator(self.current_token)
+			elif self.current_token.type in (SQRT):
+				self.evaluate_unary_operator(self.current_token)
+			elif self.current_token.type == SWAP:
+				a = self.stack.pop()
+				b = self.stack.pop()
+				self.stack.append(a)
+				self.stack.append(b)
+			elif self.current_token.type == POP:
+				self.stack.pop()
+			elif self.current_token.type in (HEX, DEC, BIN):
+				self.set_mode(self.current_token)
+			else:
+				raise InterpreterError('Unexpected token')
 
-			token = self.current_token
+			self.current_token = self.lexer.get_next_token()
 
 		return self.stack
 

lexer.py

@@ -14,6 +14,7 @@ from constants import (
 	NUMBER, EOF,
 	PLUS, MINUS, MUL, DIV, POW, SQRT,
 	HEX, DEC, BIN,
+	SWAP, POP,
 )
 
 
@@ -84,14 +85,19 @@ class Lexer():
 					text += self.current_char
 					self.advance()
 
-				if text.lower() == HEX.lower():
+				check = text.lower()
+				if check.lower() == HEX.lower():
 					return Token(HEX, hex)
-				elif text.lower() == DEC.lower():
+				elif check.lower() == DEC.lower():
 					return Token(DEC, float)
-				elif text.lower() == BIN.lower():
+				elif check.lower() == BIN.lower():
 					return Token(BIN, bin)
-				elif text.lower() == SQRT.lower():
+				elif check.lower() == SQRT.lower():
 					return Token(SQRT, math.sqrt)
+				elif check.lower() == SWAP.lower():
+					return Token(SWAP, text)
+				elif check.lower() == POP.lower():
+					return Token(POP, text)
 				else:
 					self.error(text)
 

main.py

@@ -7,7 +7,7 @@
 # Distributed under terms of the BSD-3-Clause license.
 
 from lexer import Lexer
-from interpreter import Interpreter
+from interpreter import Interpreter, InterpreterError
 from constants import DEC
 
 
@@ -37,8 +37,8 @@ def main():
 		lexer = Lexer(text)
 		try:
 			stack = interpreter.parse(lexer)
-		except Exception as exception:
-			print(exception)
+		except InterpreterError as err:
+			print(err)
 
 		print_stack(interpreter, stack)