added write, read and for statements

improved/parser.py

@@ -117,13 +117,18 @@ def arithmetic_value():
     return ((num ^ (lambda i: IntArithmeticExp(i))) |
             (imp_id  ^ (lambda v: VarArithmeticExp(v))))
 
+def read_statement():
+    def internal(parsed):
+        return ReadStatement()
+    return keyword('read') ^ internal
+
 def arithmetic_term():
     """
         Matches an arithmetic term.
 
         returns -- a parser matching an arithmetic value or group
     """
-    return arithmetic_value() | arithmetic_group()
+    return read_statement() | arithmetic_value() | arithmetic_group()
 
 def arithmetic_exp():
     """
@@ -205,10 +210,44 @@ def while_statement():
             + keyword('do') + Lazy(statements)
             + keyword('end') ^ internal)
 
+def for_statement():
+    """
+        Builds a parser for for statements.
+
+        returns -- a parser for for statements
+    """
+    def internal(parsed):
+        ((((_, condition), _), body), _) = parsed
+        return ForStatement(condition, body)
+    return (keyword('for') + arithmetic_exp()
+            + keyword('do') + Lazy(statements)
+            + keyword('end') ^ internal)
+
+def write_statement():
+    """
+        Builds a parser for write statements.
+
+        returns -- a parser for write statements
+    """
+    def internal(parsed):
+        (_, message) = parsed
+        return WriteStatement(message)
+    return keyword('write') + arithmetic_exp() ^ internal
+
 def statement():
-    return assign_statement() | if_statement() | while_statement()
+    """
+        Builds a parser for single IMP statements.
+
+        returns -- a parser for single statements in the IMP langauge
+    """
+    return write_statement() | assign_statement() | if_statement() | while_statement() | for_statement()
 
 def statements():
+    """
+        Builds a parser for multiple IMP statements.
+
+        returns -- a parser for multiple statements in the IMP language
+    """
     sep = keyword(';') ^ (lambda x: lambda l, r: CompoundStatement(l, r))
     return Exp(statement(), sep)