Implement %precedence Operator Precedence

lib/lrama/grammar.rb

@@ -103,6 +103,10 @@ def add_right(sym, precedence)
       set_precedence(sym, Precedence.new(type: :right, precedence: precedence))
     end
 
+    def add_precedence(sym, precedence)
+      set_precedence(sym, Precedence.new(type: :precedence, precedence: precedence))
+    end
+
     def set_precedence(sym, precedence)
       raise "" if sym.nterm?
       sym.precedence = precedence

lib/lrama/lexer.rb

@@ -154,6 +154,8 @@ def lex_common(lines, tokens)
           tokens << create_token(Token::P_left, ss[0], line, ss.pos - column)
         when ss.scan(/%right/)
           tokens << create_token(Token::P_right, ss[0], line, ss.pos - column)
+        when ss.scan(/%precedence/)
+          tokens << create_token(Token::P_precedence, ss[0], line, ss.pos - column)
         when ss.scan(/%prec/)
           tokens << create_token(Token::P_prec, ss[0], line, ss.pos - column)
         when ss.scan(/{/)

lib/lrama/lexer/token.rb

@@ -61,6 +61,7 @@ def self.define_type(name)
       define_type(:P_nonassoc)       # %nonassoc
       define_type(:P_left)           # %left
       define_type(:P_right)          # %right
+      define_type(:P_precedence)     # %precedence
       define_type(:P_prec)           # %prec
       define_type(:User_code)        # { ... }
       define_type(:Tag)              # <int>

lib/lrama/parser.rb

@@ -159,6 +159,14 @@ def parse_bison_declarations(ts, grammar)
             grammar.add_right(sym, precedence_number)
           end
           precedence_number += 1
+        when T::P_precedence
+          # %precedence (ident|char|string)+
+          ts.next
+          while (id = ts.consume(T::Ident, T::Char, T::String)) do
+            sym = grammar.add_term(id: id)
+            grammar.add_precedence(sym, precedence_number)
+          end
+          precedence_number += 1
         when nil
           # end of input
           raise "Reach to end of input within declarations"

lib/lrama/states.rb

@@ -455,6 +455,11 @@ def compute_shift_reduce_conflicts
 
             # shift_prec == reduce_prec, then check associativity
             case sym.precedence.type
+            when :precedence
+              # %precedence only specifies precedence and not specify associativity
+              # then a conflict is unresolved if precedence is same.
+              state.conflicts << State::ShiftReduceConflict.new(symbols: [sym], shift: shift, reduce: reduce)
+              next
             when :right
               # Shift is selected
               state.resolved_conflicts << State::ResolvedConflict.new(symbol: sym, reduce: reduce, which: :shift, same_prec: true)

spec/lrama/states_spec.rb

@@ -1157,8 +1157,8 @@ class    go to state 5
       end
     end
 
-    describe "conflict happens on nonassoc operator" do
-      it "resolved as error" do
+    describe "conflict happens on %nonassoc operator" do
+      it "resolved as 'run-time' error" do
         y = <<~INPUT
 %{
 // Prologue
@@ -1250,6 +1250,137 @@ class    go to state 5
     Conflict between rule 2 and token "=" resolved as an error (%nonassoc "=").
 
 
+        STR
+      end
+    end
+
+    describe "conflict happens on %precedence operator" do
+      it "resolved as 'run-time' error so that conflict is kept" do
+        y = <<~INPUT
+%{
+// Prologue
+%}
+
+%token NUM
+
+%precedence '+'
+%precedence '*'
+
+%%
+
+program: expr ;
+
+expr: expr '+' expr
+    | expr '*' expr
+    | NUM
+    ;
+
+%%
+        INPUT
+        grammar = Lrama::Parser.new(y).parse
+        states = Lrama::States.new(grammar, warning)
+        states.compute
+
+        str = ""
+        states.reporter.report(str, states: true, solved: true)
+
+        expect(str).to eq(<<~STR)
+State 7 conflicts: 1 shift/reduce
+State 8 conflicts: 1 shift/reduce
+
+
+State 0
+
+    0 $accept: • program "end of file"
+
+    NUM  shift, and go to state 1
+
+    program  go to state 2
+    expr     go to state 3
+
+
+State 1
+
+    4 expr: NUM •
+
+    $default  reduce using rule 4 (expr)
+
+
+State 2
+
+    0 $accept: program • "end of file"
+
+    "end of file"  shift, and go to state 4
+
+
+State 3
+
+    1 program: expr •
+    2 expr: expr • '+' expr
+    3     | expr • '*' expr
+
+    '+'  shift, and go to state 5
+    '*'  shift, and go to state 6
+
+    $default  reduce using rule 1 (program)
+
+
+State 4
+
+    0 $accept: program "end of file" •
+
+    $default  accept
+
+
+State 5
+
+    2 expr: expr '+' • expr
+
+    NUM  shift, and go to state 1
+
+    expr  go to state 7
+
+
+State 6
+
+    3 expr: expr '*' • expr
+
+    NUM  shift, and go to state 1
+
+    expr  go to state 8
+
+
+State 7
+
+    2 expr: expr • '+' expr
+    2     | expr '+' expr •
+    3     | expr • '*' expr
+
+    '+'  shift, and go to state 5
+    '*'  shift, and go to state 6
+
+    "end of file"  reduce using rule 2 (expr)
+    '+'            reduce using rule 2 (expr)
+    '*'            reduce using rule 2 (expr)
+
+    Conflict between rule 2 and token '*' resolved as shift ('+' < '*').
+
+
+State 8
+
+    2 expr: expr • '+' expr
+    3     | expr • '*' expr
+    3     | expr '*' expr •
+
+    '*'  shift, and go to state 6
+
+    "end of file"  reduce using rule 3 (expr)
+    '+'            reduce using rule 3 (expr)
+    '*'            reduce using rule 3 (expr)
+
+    Conflict between rule 3 and token '+' resolved as reduce ('+' < '*').
+
+
         STR
       end
     end