From 3d6ff5d44dcaafa60718459eda365e8b198ca3bb Mon Sep 17 00:00:00 2001
From: Robin Jadoul <robin.jadoul@gmail.com>
Date: Sun, 15 Jan 2017 14:50:51 +0100
Subject: [PATCH] Precedence resolution

---
 TODO                                  | 11 ++++++++-
 include/Parsodus/config.h             |  7 ------
 include/Parsodus/grammar.h            |  7 ++++++
 include/Parsodus/lrtables/generator.h | 34 ++++++++++++++++++++++++++-
 4 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/TODO b/TODO
index 26418e0..1960232 100644
--- a/TODO
+++ b/TODO
@@ -1,6 +1,10 @@
+-----------------------------------------------------------------------
+-                                TODO                                 -
+-----------------------------------------------------------------------
+
 T> Parser selection without enum (Thomas) (flexible matching (case insensitive, ...))
 
-R> Precedence resolution in generator
+R> Generated code error handler
 T> Parsodus regex parser in Lexesis
     -> Vrijgeven in libraryformaat: mogelijkheid verschillende tokens opvragen
 K> Parsodus Parsodus parser
@@ -36,3 +40,8 @@ R> man pages
     -> write configuration sets, table
     -> Generator: logging
     -> driver/main: debug flag
+
+-----------------------------------------------------------------------
+-                                DONE                                 -
+-----------------------------------------------------------------------
+R> Precedence resolution in generator
diff --git a/include/Parsodus/config.h b/include/Parsodus/config.h
index b96cea4..976c314 100644
--- a/include/Parsodus/config.h
+++ b/include/Parsodus/config.h
@@ -7,17 +7,10 @@
 
 namespace pds {
 
-    enum class PrecedenceType {
-        LEFT,
-        RIGHT,
-        NONASSOC
-    };
-
     struct Config {
         util::ParserType parserType;
         std::string lexesisFile;
         Grammar grammar;
-        std::map<std::string, std::pair<int, PrecedenceType> > precedence; ///< lower value -> higher precedence
     };
 
 }
diff --git a/include/Parsodus/grammar.h b/include/Parsodus/grammar.h
index 72cd2d2..c2861ea 100644
--- a/include/Parsodus/grammar.h
+++ b/include/Parsodus/grammar.h
@@ -31,6 +31,12 @@ namespace pds {
         Rule(const std::string& h, const std::vector<std::string>& t) : head(h), tail(t) {}
     };
 
+    enum class PrecedenceType {
+        LEFT,
+        RIGHT,
+        NONASSOC
+    };
+
     /**
      * A context free grammar
      * Keeps track of variables, terminals and replacement rules
@@ -40,6 +46,7 @@ namespace pds {
         std::set<std::string> variables; ///< the variables
         std::set<std::string> terminals; ///< the terminals
         std::vector<std::shared_ptr<Rule>> rules; ///< the replacement rules
+        std::map<std::string, std::pair<int, PrecedenceType> > precedence; ///< lower value -> higher precedence
 
         std::unique_ptr<util::FirstSet> first;
         std::unique_ptr<util::FollowSet> follow;
diff --git a/include/Parsodus/lrtables/generator.h b/include/Parsodus/lrtables/generator.h
index e95d35f..d78f738 100644
--- a/include/Parsodus/lrtables/generator.h
+++ b/include/Parsodus/lrtables/generator.h
@@ -132,7 +132,39 @@ LRTable Generator<Itemset>::generate() {
                 } else if (table.act[curIdx].count(term)) {
                     if (table.act[curIdx][term].first == Action::SHIFT) {
                         //Shift-Reduce conflict, rapport and resolve it (TODO)
-                        throw std::runtime_error("shift-reduce");
+                        std::string leftToken = "";
+                        for (std::size_t i = m_gram.rules[rule_applied]->tail.size(); i > 0; i--) {
+                            std::string leftSym = m_gram.rules[rule_applied]->tail[i - 1];
+                            if (m_gram.terminals.count(leftSym)) {
+                                leftToken = leftSym;
+                                break;
+                            }
+                        }
+
+                        bool handled = false;
+
+                        auto leftTokenIt = m_gram.precedence.find(leftToken);
+                        auto rightTokenIt = m_gram.precedence.find(term);
+                        if (leftTokenIt != m_gram.precedence.end() && rightTokenIt != m_gram.precedence.end()) {
+                            if (leftTokenIt->second.first > rightTokenIt->second.first) {
+                                // Keep the shift
+                                handled = true;
+                            } else if (leftTokenIt->second.first > rightTokenIt->second.first) {
+                                // replace with a reduce
+                                table.act[curIdx][term] = {Action::REDUCE, rule_applied};
+                                handled = true;
+                            } else if (leftTokenIt->second.second == PrecedenceType::LEFT) {
+                                // replace with a reduce
+                                table.act[curIdx][term] = {Action::REDUCE, rule_applied};
+                                handled = true;
+                            } else if (leftTokenIt->second.second == PrecedenceType::RIGHT) {
+                                // Keep the shift
+                                handled = true;
+                            } //Nonassoc falls through
+                        }
+
+                        if (!handled)
+                            throw std::runtime_error("shift-reduce");
                     } else if (table.act[curIdx][term].first == Action::REDUCE
                             && table.act[curIdx][term].second != rule_applied) {
                         //Reduce-Reduce conflict, rapport it (TODO)