Index: calc_plain.cpp
===================================================================
--- calc_plain.cpp	(revision 44011)
+++ calc_plain.cpp	(working copy)
@@ -41,6 +41,7 @@
     void    do_mult(char const*, char const*)   { cout << "MULTIPLY\n"; }
     void    do_div(char const*, char const*)    { cout << "DIVIDE\n"; }
     void    do_neg(char const*, char const*)    { cout << "NEGATE\n"; }
+	void    do_sqrt(char const*, char const*)   { cout << "SQRT\n"; }
 }
 
 ////////////////////////////////////////////////////////////////////////////
@@ -72,6 +73,7 @@
             factor
                 =   lexeme_d[(+digit_p)[&do_int]]
                 |   '(' >> expression >> ')'
+				|	("sqrt(" >> expression >> ")")[&do_sqrt]
                 |   ('-' >> factor)[&do_neg]
                 |   ('+' >> factor)
                 ;