match: don't modify subexpression list if expression doesn't match the pattern.

[ginac.git] / ginac / basic.cpp

diff --git a/ginac/basic.cpp b/ginac/basic.cpp
index a3de04aab9cd306eda820e8d7b50dadc492f3164..7a0633de19a18221f241292b21742416cdb29dce 100644 (file)
--- a/ginac/basic.cpp
+++ b/ginac/basic.cpp
@@ -585,12 +585,18 @@ bool basic::match(const ex & pattern, lst & repl_lst) const
                if (!match_same_type(ex_to<basic>(pattern)))
                        return false;
 
+               // Even if the expression does not match the pattern, some of
+               // its subexpressions could match it. For example, x^5*y^(-1)
+               // does not match the pattern $0^5, but its subexpression x^5
+               // does. So, save repl_lst in order to not add bogus entries.
+               lst tmp_repl = repl_lst;
                // Otherwise the subexpressions must match one-to-one
                for (size_t i=0; i<nops(); i++)
-                       if (!op(i).match(pattern.op(i), repl_lst))
+                       if (!op(i).match(pattern.op(i), tmp_repl))
                                return false;
 
                // Looks similar enough, match found
+               repl_lst = tmp_repl;
                return true;
        }
 }