diff --git a/exe/mm2ep-depend b/exe/mm2ep-depend
index 94c6eed..40114fe 100755
--- a/exe/mm2ep-depend
+++ b/exe/mm2ep-depend
@@ -20,7 +20,7 @@ module Mm2ep
         vars.each do |var|
           tab_vars[var.split('=')[0]] = var.split('=')[1]
         end
-    
+
         # Give vars name and value from shell command to parser
         parser.names=tab_vars
 
@@ -28,8 +28,11 @@ module Mm2ep
         pp token
         puts "RAW : #{line}"
         puts "EVAL: #{token.to_s}"
-        exit 1 unless token.errors.empty?
+        parser.check_grammar line, token
+        binding.pry
+        exit 1 unless token.errors.empty? || token.nil?
         puts "RESULT: #{token.compute}"
+
       end
     end
   end
diff --git a/lib/errors/invalid_grammar.rb b/lib/errors/invalid_grammar.rb
new file mode 100644
index 0000000..a3b8466
--- /dev/null
+++ b/lib/errors/invalid_grammar.rb
@@ -0,0 +1,6 @@
+module Mm2ep
+  module Depend
+    class InvalidGrammar < Depend::EvalError
+    end
+  end
+end
diff --git a/lib/errors/var_not_defined.rb b/lib/errors/var_not_defined.rb
index 11c0ed5..2ec0de1 100644
--- a/lib/errors/var_not_defined.rb
+++ b/lib/errors/var_not_defined.rb
@@ -1,7 +1,6 @@
 module Mm2ep
   module Depend
     class VarNotDefined < Depend::EvalError
-    
     end
   end
 end
diff --git a/lib/mm2ep_depend.rb b/lib/mm2ep_depend.rb
index ef6197f..c5dacf9 100644
--- a/lib/mm2ep_depend.rb
+++ b/lib/mm2ep_depend.rb
@@ -10,3 +10,4 @@ require 'mm2ep_depend/lexer'
 require 'mm2ep_depend/parser'
 require 'mm2ep_depend/eval_error'
 require 'errors/var_not_defined'
+require 'errors/invalid_grammar'
diff --git a/lib/mm2ep_depend/eval_error.rb b/lib/mm2ep_depend/eval_error.rb
index df75bcb..4425a1a 100644
--- a/lib/mm2ep_depend/eval_error.rb
+++ b/lib/mm2ep_depend/eval_error.rb
@@ -12,7 +12,6 @@ module Mm2ep
         @message = hash[:message]
         @var = hash[:var]
       end
-
     end
   end
 end
diff --git a/lib/mm2ep_depend/parser.rb b/lib/mm2ep_depend/parser.rb
index aab4c80..2329b1d 100755
--- a/lib/mm2ep_depend/parser.rb
+++ b/lib/mm2ep_depend/parser.rb
@@ -1,17 +1,13 @@
 module Mm2ep
   module Depend
     class TreeExpr
-
       def compute
         raise NotImplementedError
       end
     end
 
     class TreeValue
-
-      def value
-        @value
-      end
+      attr_reader :value
 
       def to_s
         raise NotImplementedError
@@ -29,12 +25,11 @@ module Mm2ep
                  when /false/i then false
                  else value
                  end
-        if @value.nil?
-          @errors << VarNotDefined.new(
-            message:"No value for #{@name}",
-            var: @name
-            )
-        end
+        return unless @value.nil?
+        @errors << VarNotDefined.new(
+          message: "No value for #{@name}",
+          var: @name
+        )
       end
 
       def compute
@@ -167,7 +162,6 @@ module Mm2ep
         @errors.concat rval.errors
         @lval = lval
         @rval = rval
-
       end
 
       def compute
@@ -181,10 +175,16 @@ module Mm2ep
 
     class Parser < Rly::Yacc
       attr_writer :names
-      attr_reader :errors
-      # def names(tab)
-      #   @names = tab
-      # end
+
+      def check_grammar(line, tokens)
+        grammar = tokens.to_s.split(/=|AND|OR/)
+        expr = line.split(/=|AND|OR/)
+        return if grammar.size == expr.size
+        return if grammar.empty?
+        tokens.errors << InvalidGrammar.new(
+          message: 'Invalid Grammar'
+        )
+      end
 
       precedence :left, :OR_OP
       precedence :left, :AND_OP
@@ -232,7 +232,6 @@ module Mm2ep
       end
 
       rule 'expr : VAR EQ_OP bool_expr' do |ex, v, _eq, n|
-        # binding.pry
         ex.value = EqOp.new(
           VarValue.new(v.value.to_s, @names[v.value]),
           BoolValue.new(n.value)
diff --git a/spec/files/grammar_completely_invalid.txt b/spec/files/grammar_completely_invalid.txt
new file mode 100644
index 0000000..34d777f
--- /dev/null
+++ b/spec/files/grammar_completely_invalid.txt
@@ -0,0 +1 @@
+false = "Arya"
diff --git a/spec/files/grammar_partially_invalid.txt b/spec/files/grammar_partially_invalid.txt
new file mode 100644
index 0000000..5724920
--- /dev/null
+++ b/spec/files/grammar_partially_invalid.txt
@@ -0,0 +1 @@
+( a_girl_has_no_name = true ) ANDAND ( character = "Arya Stark" ) OR false AND true
diff --git a/spec/mm2ep_depend/parser_spec.rb b/spec/mm2ep_depend/parser_spec.rb
new file mode 100644
index 0000000..ff4250b
--- /dev/null
+++ b/spec/mm2ep_depend/parser_spec.rb
@@ -0,0 +1,46 @@
+require 'spec_helper'
+require 'mm2ep_depend'
+
+describe Mm2ep::Depend::Parser do
+  it 'has to report var which is not defined' do
+    line = File.read(testfile('simple_eq_expr_boolexpr.txt')).delete("\n")
+    parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
+    parser.names = {}
+    token = parser.parse(line.chomp)
+    token.errors
+         .select do |elem|
+      elem.is_a? Mm2ep::Depend::VarNotDefined
+    end.size.must_equal 1
+  end
+
+  it 'has to report vars which are not defined' do
+    line = File.read(testfile('simple_expr_or_expr.txt')).delete("\n")
+    parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
+    parser.names = {}
+    token = parser.parse(line.chomp)
+    token.errors
+         .select do |elem|
+      elem.is_a? Mm2ep::Depend::VarNotDefined
+    end.size.must_equal 2
+  end
+
+  it 'has to report invalid_grammar' do
+    line = File.read(testfile('grammar_partially_invalid.txt')).delete("\n")
+    parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
+    parser.names = { 'a_girl_has_no_name' => true, 'character' => 'Arya Stark' }
+    token = parser.parse(line.chomp)
+    parser.check_grammar line, token
+    token.errors.select do |elem|
+      elem.is_a? Mm2ep::Depend::InvalidGrammar
+    end.size.must_equal 1
+  end
+
+  it 'has to be nil when grammar is completely invalid' do
+    line = File.read(testfile('grammar_completely_invalid.txt')).delete("\n")
+    parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
+    parser.names = {}
+    token = parser.parse(line.chomp)
+    parser.check_grammar line, token
+    assert_nil token
+  end
+end
diff --git a/spec/mm2ep_depend/priority_parser_spec.rb b/spec/mm2ep_depend/priority_parser_spec.rb
index 902ad70..3774eec 100644
--- a/spec/mm2ep_depend/priority_parser_spec.rb
+++ b/spec/mm2ep_depend/priority_parser_spec.rb
@@ -2,7 +2,6 @@ require 'spec_helper'
 require 'mm2ep_depend'
 
 describe Mm2ep::Depend::Parser do
-
   it 'has to do not before or' do
     line = File.read(testfile('priority_not_or.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
@@ -30,5 +29,4 @@ describe Mm2ep::Depend::Parser do
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
-
 end
diff --git a/spec/mm2ep_depend/simple_expr_parser_spec.rb b/spec/mm2ep_depend/simple_expr_parser_spec.rb
index 4e2ef3b..ba2d340 100644
--- a/spec/mm2ep_depend/simple_expr_parser_spec.rb
+++ b/spec/mm2ep_depend/simple_expr_parser_spec.rb
@@ -2,7 +2,6 @@ require 'spec_helper'
 require 'mm2ep_depend'
 
 describe Mm2ep::Depend::Parser do
-
   it 'has to apply not on expr' do
     line = File.read(testfile('simple_not_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
@@ -13,7 +12,7 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate eq with bool expr and return true' do
     line = File.read(testfile('simple_eq_expr_boolexpr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'true'}
+    parser.names = { 'truc_bidule' => 'true' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -21,7 +20,7 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate eq with bool expr and return false' do
     line = File.read(testfile('simple_eq_expr_boolexpr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'false'}
+    parser.names = { 'truc_bidule' => 'false' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
@@ -29,7 +28,7 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate eq with number and return true' do
     line = File.read(testfile('simple_eq_expr_number.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => '10'}
+    parser.names = { 'truc_bidule' => '10' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -37,7 +36,7 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate eq with number and return false' do
     line = File.read(testfile('simple_eq_expr_number.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => '11'}
+    parser.names = { 'truc_bidule' => '11' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
@@ -45,7 +44,7 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate eq with string and return true' do
     line = File.read(testfile('simple_eq_expr_string.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'test'}
+    parser.names = { 'truc_bidule' => 'test' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -53,7 +52,7 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate eq with string and return false' do
     line = File.read(testfile('simple_eq_expr_string.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'tes'}
+    parser.names = { 'truc_bidule' => 'tes' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
@@ -61,9 +60,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate true OR true and return true' do
     line = File.read(testfile('simple_expr_or_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'true',
-                  'machin' => 'true'
-                 }
+    parser.names = { 'truc_bidule' => 'true',
+                     'machin' => 'true' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -71,9 +69,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate true OR false and return true' do
     line = File.read(testfile('simple_expr_or_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'true',
-                  'machin' => 'false'
-                 }
+    parser.names = { 'truc_bidule' => 'true',
+                     'machin' => 'false' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -81,9 +78,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate false OR true and return true' do
     line = File.read(testfile('simple_expr_or_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'false',
-                  'machin' => 'true'
-                 }
+    parser.names = { 'truc_bidule' => 'false',
+                     'machin' => 'true' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -91,9 +87,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate false OR false and return false' do
     line = File.read(testfile('simple_expr_or_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'false',
-                  'machin' => 'false'
-                 }
+    parser.names = { 'truc_bidule' => 'false',
+                     'machin' => 'false' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
@@ -101,9 +96,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate true AND true and return true' do
     line = File.read(testfile('simple_expr_and_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'true',
-                  'machin' => 'true'
-                 }
+    parser.names = { 'truc_bidule' => 'true',
+                     'machin' => 'true' }
     token = parser.parse(line.chomp)
     assert_equal(true, token.compute)
   end
@@ -111,9 +105,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate true AND false and return false' do
     line = File.read(testfile('simple_expr_and_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'true',
-                  'machin' => 'false'
-                 }
+    parser.names = { 'truc_bidule' => 'true',
+                     'machin' => 'false' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
@@ -121,9 +114,8 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate false AND true and return false' do
     line = File.read(testfile('simple_expr_and_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'false',
-                  'machin' => 'true'
-                 }
+    parser.names = { 'truc_bidule' => 'false',
+                     'machin' => 'true' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
@@ -131,11 +123,9 @@ describe Mm2ep::Depend::Parser do
   it 'has to evaluate false AND false and return false' do
     line = File.read(testfile('simple_expr_and_expr.txt')).delete("\n")
     parser = Mm2ep::Depend::Parser.new(Mm2ep::Depend::Lexer.new)
-    parser.names={'truc_bidule' => 'false',
-                  'machin' => 'false'
-                 }
+    parser.names = { 'truc_bidule' => 'false',
+                     'machin' => 'false' }
     token = parser.parse(line.chomp)
     assert_equal(false, token.compute)
   end
-
 end