- first implementation of pattern matching

[ginac.git] / ginac / basic.cpp

diff --git a/ginac/basic.cpp b/ginac/basic.cpp
index bf5bd6cb02b0d1c89e8b87acdc000a0913108ebb..c899d19f1659c2641d3b4048108bf5b90019c5f7 100644 (file)
--- a/ginac/basic.cpp
+++ b/ginac/basic.cpp
@@ -33,6 +33,7 @@
 #include "symbol.h"
 #include "lst.h"
 #include "ncmul.h"
+#include "relational.h"
 #include "print.h"
 #include "archive.h"
 #include "utils.h"
@@ -219,7 +220,8 @@ ex basic::operator[](int i) const
 bool basic::has(const ex & other) const
 {
        GINAC_ASSERT(other.bp!=0);
-       if (is_equal(*other.bp)) return true;
+       lst repl_lst;
+       if (match(*other.bp, repl_lst)) return true;
        if (nops()>0) {
                for (unsigned i=0; i<nops(); i++)
                        if (op(i).has(other))
@@ -398,15 +400,66 @@ bool basic::contract_with(exvector::iterator self, exvector::iterator other, exv
        return false;
 }
 
+/** Check whether the expression matches a given pattern. For every wildcard
+ *  object in the pattern, an expression of the form "wildcard == matching_expression"
+ *  is added to repl_lst. */
+bool basic::match(const ex & pattern, lst & repl_lst) const
+{
+//clog << "match " << *this << " with " << pattern << ", repl_lst = " << repl_lst << endl;
+       if (is_ex_exactly_of_type(pattern, wildcard)) {
+
+               // Wildcard matches anything, but check whether we already have found
+               // a match for that wildcard first (if so, it the earlier match must
+               // be the same expression)
+               for (unsigned i=0; i<repl_lst.nops(); i++) {
+                       if (repl_lst.op(i).op(0).is_equal(pattern))
+                               return is_equal(*repl_lst.op(i).op(1).bp);
+               }
+               repl_lst.append(pattern == *this);
+               return true;
+
+       } else {
+
+               // Expression must be of the same type as the pattern
+               if (tinfo() != pattern.bp->tinfo())
+                       return false;
+
+               // Number of subexpressions must match
+               if (nops() != pattern.nops())
+                       return false;
+
+               // No subexpressions? Then just compare the objects (there can't be
+               // wildcards in the pattern)
+               if (nops() == 0)
+                       return is_equal(*pattern.bp);
+
+               // Otherwise the subexpressions must match one-to-one
+               for (unsigned i=0; i<nops(); i++)
+                       if (!op(i).match(pattern.op(i), repl_lst))
+                               return false;
+
+               // Looks similar enough, match found
+               return true;
+       }
+}
+
 /** Substitute a set of objects by arbitrary expressions. The ex returned
  *  will already be evaluated. */
-ex basic::subs(const lst & ls, const lst & lr) const
+ex basic::subs(const lst & ls, const lst & lr, bool no_pattern) const
 {
        GINAC_ASSERT(ls.nops() == lr.nops());
 
-       for (unsigned i=0; i<ls.nops(); i++) {
-               if (is_equal(*ls.op(i).bp))
-                       return lr.op(i);
+       if (no_pattern) {
+               for (unsigned i=0; i<ls.nops(); i++) {
+                       if (is_equal(*ls.op(i).bp))
+                               return lr.op(i);
+               }
+       } else {
+               for (unsigned i=0; i<ls.nops(); i++) {
+                       lst repl_lst;
+                       if (match(*ls.op(i).bp, repl_lst))
+                               return lr.op(i).bp->subs(repl_lst, true); // avoid recursion when re-substituting the wildcards
+               }
        }
 
        return *this;
@@ -535,10 +588,10 @@ ex basic::expand(unsigned options) const
  *  replacement arguments: 1) a relational like object==ex and 2) a list of
  *  relationals lst(object1==ex1,object2==ex2,...), which is converted to
  *  subs(lst(object1,object2,...),lst(ex1,ex2,...)). */
-ex basic::subs(const ex & e) const
+ex basic::subs(const ex & e, bool no_pattern) const
 {
        if (e.info(info_flags::relation_equal)) {
-               return subs(lst(e));
+               return subs(lst(e), no_pattern);
        }
        if (!e.info(info_flags::list)) {
                throw(std::invalid_argument("basic::subs(ex): argument must be a list"));
@@ -553,7 +606,7 @@ ex basic::subs(const ex & e) const
                ls.append(r.op(0));
                lr.append(r.op(1));
        }
-       return subs(ls, lr);
+       return subs(ls, lr, no_pattern);
 }
 
 /** Compare objects to establish canonical ordering.