Add sqrt operator

constants.py

@@ -14,6 +14,7 @@ MINUS = 'MINUS'
 MUL = 'MUL'
 DIV = 'DIV'
 POW = 'POW'
+SQRT = 'SQRT'
 
 HEX = 'HEX'
 DEC = 'DEC'

interpreter.py

@@ -8,7 +8,7 @@
 
 from constants import (
 	NUMBER, EOF,
-	PLUS, MINUS, MUL, DIV, POW,
+	PLUS, MINUS, MUL, DIV, POW, SQRT,
 	HEX, DEC, BIN,
 )
 
@@ -40,7 +40,7 @@ class Interpreter:
 
 		return value
 
-	def evaluate_operator(self, token):
+	def evaluate_binary_operator(self, token):
 		if len(self.stack) < 2:
 			raise Exception('Needs at least 2 values on the stack')
 
@@ -49,6 +49,14 @@ class Interpreter:
 		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')
+
+		value = self.get_from_stack()
+		self.stack.append(token.value(value))
+		self.eat(token.type)
+
 	def set_mode(self, token):
 		self.mode = token.type
 		self.mode_func = token.value
@@ -59,7 +67,9 @@ class Interpreter:
 
 		while token.type is not EOF:
 			if token.type in (PLUS, MINUS, MUL, DIV, POW):
-				self.evaluate_operator(token)
+				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)

lexer.py

@@ -6,12 +6,13 @@
 #
 # Distributed under terms of the BSD-3-Clause license.
 
+import math
 import operator
 
 from token import Token
 from constants import (
 	NUMBER, EOF,
-	PLUS, MINUS, MUL, DIV, POW,
+	PLUS, MINUS, MUL, DIV, POW, SQRT,
 	HEX, DEC, BIN,
 )
 
@@ -83,12 +84,14 @@ class Lexer():
 					text += self.current_char
 					self.advance()
 
-				if text.lower() == 'hex':
+				if text.lower() == HEX.lower():
 					return Token(HEX, hex)
-				elif text.lower() == 'dec':
+				elif text.lower() == DEC.lower():
 					return Token(DEC, float)
-				elif text.lower() == 'bin':
+				elif text.lower() == BIN.lower():
 					return Token(BIN, bin)
+				elif text.lower() == SQRT.lower():
+					return Token(SQRT, math.sqrt)
 				else:
 					self.error(text)