From 982d385ea371e331f7d2285b2316d4ea160e7c89 Mon Sep 17 00:00:00 2001
From: Robin Jadoul <robin.jadoul@gmail.com>
Date: Fri, 20 Jan 2017 20:05:41 +0100
Subject: [PATCH] LR support for explicit rule precedences

---
 TODO                                  |  2 +-
 include/Parsodus/grammar.h            | 13 +++++++------
 include/Parsodus/lrtables/generator.h | 21 ++++++---------------
 3 files changed, 14 insertions(+), 22 deletions(-)

diff --git a/TODO b/TODO
index f36df7e..597cefa 100644
--- a/TODO
+++ b/TODO
@@ -5,7 +5,7 @@
 T> Parsodus regex parser in Lexesis
     -> Vrijgeven in libraryformaat: mogelijkheid verschillende tokens opvragen
 K> Parsodus Parsodus parser
-    -> Precedence
+    -> Precedence + fill precedence in rules
     -> rule naming (problem: multiple rules same name -> change in backend)
         -> grammar struct change to contain optional name per rule
     -> Volgorde belangrijk?
diff --git a/include/Parsodus/grammar.h b/include/Parsodus/grammar.h
index 8b58a3a..73b1a9f 100644
--- a/include/Parsodus/grammar.h
+++ b/include/Parsodus/grammar.h
@@ -11,6 +11,12 @@
 #include <vector>
 
 namespace pds {
+    enum class PrecedenceType {
+        LEFT,
+        RIGHT,
+        NONASSOC
+    };
+
     /**
      * Represents a grammar rule
      * head -> tail[0] tail[1] ... tail[tail.size() - 1]
@@ -19,6 +25,7 @@ namespace pds {
         std::string head; ///< The replaced variable
         std::vector<std::string> tail; ///< The replacement rule
         const std::string name; ///< An optional name for this rule, if it's empty, there's no name
+        std::pair<bool, std::pair<int, PrecedenceType>> precedence; ///< precedence for this rule, the bool indicates whether it's valid (invalid if there is no rightmost terminal and no explicit precedence)
 
         bool operator<(const Rule& other) const {
             if(head != other.head){
@@ -33,12 +40,6 @@ namespace pds {
         Rule(const std::string& h, const std::vector<std::string>& t, const std::string& name) : head(h), tail(t), name(name) {}
     };
 
-    enum class PrecedenceType {
-        LEFT,
-        RIGHT,
-        NONASSOC
-    };
-
     /**
      * A context free grammar
      * Keeps track of variables, terminals and replacement rules
diff --git a/include/Parsodus/lrtables/generator.h b/include/Parsodus/lrtables/generator.h
index d78f738..5fb0cd4 100644
--- a/include/Parsodus/lrtables/generator.h
+++ b/include/Parsodus/lrtables/generator.h
@@ -132,32 +132,23 @@ 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)
-                        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) {
+                        if (m_gram.rules[rule_applied]->precedence.first && rightTokenIt != m_gram.precedence.end()) {
+                            auto& leftPrec = m_gram.rules[rule_applied]->precedence.second;
+                            if (leftPrec.first > rightTokenIt->second.first) {
                                 // Keep the shift
                                 handled = true;
-                            } else if (leftTokenIt->second.first > rightTokenIt->second.first) {
+                            } else if (leftPrec.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) {
+                            } else if (leftPrec.second == PrecedenceType::LEFT) {
                                 // replace with a reduce
                                 table.act[curIdx][term] = {Action::REDUCE, rule_applied};
                                 handled = true;
-                            } else if (leftTokenIt->second.second == PrecedenceType::RIGHT) {
+                            } else if (leftPrec.second == PrecedenceType::RIGHT) {
                                 // Keep the shift
                                 handled = true;
                             } //Nonassoc falls through