diff --git a/spec/crystal-dfa/nfa_spec.cr b/spec/crystal-dfa/nfa_spec.cr
index 21dc54b..2e10adf 100644
--- a/spec/crystal-dfa/nfa_spec.cr
+++ b/spec/crystal-dfa/nfa_spec.cr
@@ -8,7 +8,7 @@ describe DFA::NFA do
       DFA::NFA.create_nfa(ast).should eq expected
     end
 
-    it "creates a state for a ConcateNode" do
+    context "creates a state for a ConcateNode" do
       it "works for the binary case" do
         ast = DFA::AST::ConcatNode.new [
           DFA::AST::LiteralNode.new('a').as(DFA::AST::ASTNode),
@@ -31,7 +31,7 @@ describe DFA::NFA do
       end
     end
 
-    it "creates a state for an AlternationNode" do
+    context "creates a state for an AlternationNode" do
       it "works for the binary case" do
         ast = DFA::AST::AlternationNode.new [
           DFA::AST::LiteralNode.new('a').as(DFA::AST::ASTNode),
@@ -99,7 +99,7 @@ describe DFA::NFA do
         DFA::NFA.create_nfa(ast).should eq expected
       end
 
-      it "creates a state for a CharacterClassNode([a-z]) One-or-More" do
+      context "creates a state for a CharacterClassNode([a-z]) One-or-More" do
         it "creates a state for the simple range case [a-z]" do
           ast = DFA::AST::CharacterClassNode.new(false, Array(String).new, [('a'..'z')])
           expected = r_state('a', 'z')
diff --git a/src/core_ext/range.cr b/src/core_ext/range.cr
index 7722575..05bd183 100644
--- a/src/core_ext/range.cr
+++ b/src/core_ext/range.cr
@@ -47,7 +47,7 @@ module IntersectionMethods(T)
   end
 end
 
-struct Tuple(T)
+struct Tuple(*T)
   include IntersectionMethods(T)
 
   def -(other : self)
diff --git a/src/crystal-dfa/parser.cr b/src/crystal-dfa/parser.cr
index b3413e6..d85c2ed 100644
--- a/src/crystal-dfa/parser.cr
+++ b/src/crystal-dfa/parser.cr
@@ -143,19 +143,19 @@ module DFA
     end
 
     class NameParslet < PrefixParslet
-      def parse(parser, token)
+      def parse(parser, token) : AST::LiteralNode
         AST::LiteralNode.new(token[:value].not_nil!)
       end
     end
 
     class AnyCharacterParslet < PrefixParslet
-      def parse(parser, token)
+      def parse(parser, token) : AST::CharacterClassNode
         AST::CharacterClassNode.new(false, Array(String).new, ANY_CHAR_RANGES)
       end
     end
 
     class SpecialCharacterClassParslet < PrefixParslet
-      def parse(parser, token)
+      def parse(parser, token) : AST::ASTNode
         _next = parser.consume
         raise "unexpected end of input" unless _next
 
@@ -180,7 +180,7 @@ Lexer::IDENTIFIERS.key_for(_next[:type])
     end
 
     class GroupParslet < PrefixParslet
-      def parse(parser, token)
+      def parse(parser, token) : AST::GroupNode
         # ignore non capturing group designators
         if (_peek = parser.peek) &&
            _peek[:type] == :QSTM
@@ -199,7 +199,7 @@ Lexer::IDENTIFIERS.key_for(_next[:type])
     end
 
     class CharacterRangeParslet < InfixParslet
-      def parse(parser, left, token)
+      def parse(parser, left, token) : AST::CharacterRangeNode
         parser.consume(:MINUS)
         right = parser.parseExpression(precedence)
 
@@ -218,7 +218,7 @@ Lexer::IDENTIFIERS.key_for(_next[:type])
     end
 
     class CharacterClassParslet < PrefixParslet
-      def parse(parser, token)
+      def parse(parser, token) : AST::CharacterClassNode | AST::AlternationNode
         negate = (peek = parser.peek) &&
                  (peek[:type] == :NEGATE) &&
                  parser.consume ? true : false
@@ -266,7 +266,7 @@ Lexer::IDENTIFIERS.key_for(_next[:type])
     end
 
     class ConcatParslet < InfixParslet
-      def parse(parser, left : AST::ASTNode, token)
+      def parse(parser, left : AST::ASTNode, token) : AST::ConcatNode
         exp = AST::ConcatNode.new([left.as(AST::ASTNode)])
 
         _next = parser.parseExpression(Precedence[:LITERAL] - 1).as(AST::ASTNode?)
@@ -282,7 +282,7 @@ Lexer::IDENTIFIERS.key_for(_next[:type])
     end
 
     class CurlyQuantifierParslet < InfixParslet
-      def parse(parser, left : AST::ASTNode, token)
+      def parse(parser, left : AST::ASTNode, token) : AST::QuantifierNode
         parser.consume(:LCURLY)
 
         values = parse_quantifications(
@@ -318,14 +318,14 @@ Lexer::IDENTIFIERS.key_for(_next[:type])
     end
 
     class QuantifierParslet(T) < InfixParslet
-      def parse(parser, left : AST::ASTNode, token)
+      def parse(parser, left : AST::ASTNode, token) : AST::ASTNode
         parser.consume
         T.new(left)
       end
     end
 
     class AlternationParslet < InfixParslet
-      def parse(parser, left : AST::ASTNode, token)
+      def parse(parser, left : AST::ASTNode, token) : AST::AlternationNode
         exp = AST::AlternationNode.new([left.as(AST::ASTNode)])
         while (peek = parser.peek) && (peek[:type] == :PIPE)
           parser.consume