started working on syntax tree

ast.py

@@ -0,0 +1,25 @@
+class Node:
+    def __init__(self, type, children=None, leaf=None):
+        self.type = type
+        if children:
+            self.children = children
+        else:
+            self.children = []
+        self.leaf = leaf
+
+
+class Expr: pass
+
+
+class BinOp(Expr):
+    def __init__(self, left, op, right):
+        self.type = "binop"
+        self.left = left
+        self.right = right
+        self.op = op
+
+
+class Number(Expr):
+    def __init__(self, value):
+        self.type = "number"
+        self.value = value

parser.py

@@ -2,6 +2,7 @@
 
 import scanner
 import ply.yacc as yacc
+from ast import *
 
 tokens = scanner.tokens
 
@@ -41,11 +42,33 @@ def p_instructions_2(p):
     """instructions : instruction """
 
 
-# to finish the grammar
-# ....
+def p_expression_binop(p):
+    '''expression : expression + expression
+                  | expression - expression
+                  | expression * expression
+                  | expression / expression
+                  | expression < expression
+                  | expression > expression
+                  | expression DOTADD expression
+                  | expression DOTSUB expression
+                  | expression DOTMUL expression
+                  | expression DOTDIV expression
+                  | expression EQ expression
+                  | expression LTE expression
+                  | expression GTE expression
+                  | expression NE expression '''
 
+    p[0] = BinOp(p[1], p[2], p[3])
 
 
+def p_expression_group(p):
+    'expression : LPAREN expression RPAREN'
+    p[0] = p[2]
+
+
+def p_expression_number(p):
+    'expression : NUMBER'
+    p[0] = Number(p[1])
 
 
 parser = yacc.yacc()