From e3a1789b3fa238c82f404222e84ac8a7a551af2c Mon Sep 17 00:00:00 2001
From: Paul Beckingham <paul@beckingham.net>
Date: Sun, 27 Apr 2014 10:07:11 -0700
Subject: [PATCH] Eval

- Added support for compiled expressions that are compiled once and
  evaluated multiple times in different contexts.
---
 src/Eval.cpp | 35 +++++++++++++++++++++++++++++++++++
 src/Eval.h   |  3 +++
 2 files changed, 38 insertions(+)

diff --git a/src/Eval.cpp b/src/Eval.cpp
index 67fa6c8cc..a6e46c1a5 100644
--- a/src/Eval.cpp
+++ b/src/Eval.cpp
@@ -159,6 +159,41 @@ void Eval::evaluatePostfixExpression (const std::string& e, Variant& v) const
   evaluatePostfixStack (tokens, v);
 }
 
+////////////////////////////////////////////////////////////////////////////////
+void Eval::compileExpression (const std::string& e)
+{
+  // Reduce e to a vector of tokens.
+  Lexer l (e);
+  l.ambiguity (_ambiguity);
+  std::string token;
+  Lexer::Type type;
+  while (l.token (token, type))
+  {
+    _compiled.push_back (std::pair <std::string, Lexer::Type> (token, type));
+    if (_debug)
+      std::cout << "# token postfix '" << token << "' " << Lexer::type_name (type) << "\n";
+  }
+
+  // Parse for syntax checking and operator replacement.
+  infixParse (_compiled);
+  if (_debug)
+  {
+    std::vector <std::pair <std::string, Lexer::Type> >::iterator i;
+    for (i = _compiled.begin (); i != _compiled.end (); ++i)
+      std::cout << "# token infix '" << i->first << "' " << Lexer::type_name (i->second) << "\n";
+  }
+
+  // Convert infix --> postfix.
+  infixToPostfix (_compiled);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void Eval::evaluateCompiledExpression (Variant& v)
+{
+  // Call the postfix evaluator.
+  evaluatePostfixStack (_compiled, v);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 void Eval::ambiguity (bool value)
 {
diff --git a/src/Eval.h b/src/Eval.h
index 11219894b..dbbb02c0e 100644
--- a/src/Eval.h
+++ b/src/Eval.h
@@ -44,6 +44,8 @@ public:
   void addSource (bool (*fn)(const std::string&, Variant&));
   void evaluateInfixExpression (const std::string&, Variant&) const;
   void evaluatePostfixExpression (const std::string&, Variant&) const;
+  void compileExpression (const std::string&);
+  void evaluateCompiledExpression (Variant&);
   void ambiguity (bool);
   void debug ();
 
@@ -69,6 +71,7 @@ private:
   std::vector <bool (*)(const std::string&, Variant&)> _sources;
   bool _ambiguity;
   bool _debug;
+  std::vector <std::pair <std::string, Lexer::Type> > _compiled;
 };