diff --git a/README.md b/README.md
index 0e497eb..7eba5a8 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,6 @@ To run REPL locally: `rake run`
 To run the test suite: `rake test`
 
 # BUGs
-  * var1 var2 +|-|*|\ ===> result in on stack (normal) AND stored in var1 (_bug_)
 
 # TODO-list
   * pseudo filesystem: subdir/namespace for variables
diff --git a/lib/rpl/parser.rb b/lib/rpl/parser.rb
index 5c38919..ce919ed 100644
--- a/lib/rpl/parser.rb
+++ b/lib/rpl/parser.rb
@@ -1,5 +1,13 @@
 # frozen_string_literal: true
 
+class RplTypeError < StandardError
+  attr_reader :reason
+
+  def initialize( reason = "-undefined-" )
+    @reason = reason
+  end
+end
+
 class Parser
   include Types
 
@@ -68,7 +76,7 @@ class Parser
     end
 
     # 2. parse
-    regrouped_input.map do |element|
+    parsed_input = regrouped_input.map do |element|
       if RplBoolean.can_parse?( element )
         Types.new_object( RplBoolean, element )
       elsif RplNumeric.can_parse?( element )
@@ -83,5 +91,7 @@ class Parser
         Types.new_object( RplName, element )
       end
     end
+
+    parsed_input
   end
 end
diff --git a/lib/rpl/types/string.rb b/lib/rpl/types/string.rb
index 3d1d649..9318765 100644
--- a/lib/rpl/types/string.rb
+++ b/lib/rpl/types/string.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'rpl/parser'
+
 module Types
   class RplString
     attr_accessor :value
diff --git a/lib/rpl/words/operations.rb b/lib/rpl/words/operations.rb
index 39310b9..e639aff 100644
--- a/lib/rpl/words/operations.rb
+++ b/lib/rpl/words/operations.rb
@@ -25,56 +25,50 @@ module RplLang
                                 args.reverse!
 
                                 result = if args[0].instance_of?( RplList )
-                                           if args[1].instance_of?( RplList )
-                                             args[0].value.concat( args[1].value )
-                                           else
-                                             args[0].value << args[1]
-                                           end
-                                           args[0]
+                                           new_list = if args[1].instance_of?( RplList )
+                                                        RplList.new( args[0].to_s ).value.concat( args[1].value )
+                                                      else
+                                                        RplList.new( args[0].to_s ).value.concat( [ args[1] ] )
+                                                      end
+
+                                           RplList.new( "{ #{new_list.join(' ')} }" )
 
                                          elsif args[1].instance_of?( RplList )
-                                           if args[0].instance_of?( RplList )
-                                             args[0].value.concat( args[1].value )
-                                             args[0]
-                                           else
-                                             args[1].value.unshift( args[0] )
-                                             args[1]
-                                           end
+                                           new_list = if args[0].instance_of?( RplList )
+                                                        RplList.new( args[0].to_s ).value.concat( args[1].value )
+                                                      else
+                                                        RplList.new( "{ #{args[0]} }" ).value.concat( args[1].value )
+                                                      end
+
+                                           RplList.new( "{ #{new_list.join(' ')} }" )
 
                                          elsif args[0].instance_of?( RplString )
-                                           args[0].value = if args[1].instance_of?( RplString ) ||
+                                           RplString.new( if args[1].instance_of?( RplString ) ||
                                                               args[1].instance_of?( RplName )
-                                                             "#{args[0].value}#{args[1].value}"
-                                                           else
-                                                             "#{args[0].value}#{args[1]}"
-                                                           end
-                                           args[0]
+                                                            "\"#{args[0].value}#{args[1].value}\""
+                                                          else
+                                                            "\"#{args[0].value}#{args[1]}\""
+                                                          end )
 
                                          elsif args[0].instance_of?( RplName )
 
                                            if args[1].instance_of?( RplName )
-                                             args[0].value = "#{args[0].value}#{args[1].value}"
-                                             args[0]
+                                             RplName.new( "'#{args[0].value}#{args[1].value}'" )
+                                           elsif args[1].instance_of?( RplString )
+                                             Types.new_object( RplString, "\"#{args[0].value}#{args[1].value}\"" )
+                                           elsif args[1].instance_of?( RplNumeric )
+                                             RplName.new( "'#{args[0].value}#{args[1]}'" )
                                            else
-                                             if args[1].instance_of?( RplString )
-                                               Types.new_object( RplString, "\"#{args[0].value}#{args[1].value}\"" )
-                                             elsif args[1].instance_of?( RplNumeric )
-                                               args[0].value = "#{args[0].value}#{args[1]}"
-                                               args[0]
-                                             else
-                                               Types.new_object( RplString, "\"#{args[0]}#{args[1]}\"" )
-                                             end
+                                             Types.new_object( RplString, "\"#{args[0]}#{args[1]}\"" )
                                            end
 
                                          elsif args[0].instance_of?( RplNumeric )
                                            if args[1].instance_of?( RplNumeric )
-                                             args[0].value += args[1].value
-                                             args[0]
-
-                                           elsif args[1].instance_of?( RplString ) ||
-                                                 args[1].instance_of?( RplName )
-                                             args[1].value = "#{args[0]}#{args[1].value}"
-                                             args[1]
+                                             RplNumeric.new( args[0].value + args[1].value, args[0].base )
+                                           elsif args[1].instance_of?( RplString )
+                                             RplString.new( "\"#{args[0]}#{args[1].value}\"" )
+                                           elsif args[1].instance_of?( RplName )
+                                             RplName.new( "'#{args[0]}#{args[1].value}'" )
                                            end
                                          end
 
@@ -87,9 +81,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = args[1].value - args[0].value
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[1].value - args[0].value, args[1].base )
                               end )
 
         @dictionary.add_word( ['chs'],
@@ -105,9 +97,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = args[1].value * args[0].value
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[1].value * args[0].value, args[1].base )
                               end )
 
         @dictionary.add_word( ['÷', '/'],
@@ -116,9 +106,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = args[1].value / args[0].value
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[1].value / args[0].value, args[1].base )
                               end )
 
         @dictionary.add_word( ['inv'],
@@ -134,9 +122,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = args[1].value**args[0].value
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[1].value**args[0].value, args[1].base )
                               end )
 
         @dictionary.add_word( ['√', 'sqrt'],
@@ -145,9 +131,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = BigMath.sqrt( args[0].value, RplNumeric.precision )
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( BigMath.sqrt( args[0].value, RplNumeric.precision ), args[0].base )
                               end )
 
         @dictionary.add_word( ['²', 'sq'],
@@ -163,9 +147,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = args[0].value.abs
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( args[0].value.abs, args[0].base )
                               end )
 
         @dictionary.add_word( ['dec'],
@@ -195,9 +177,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].base = args[0].value
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[1].value, args[0].value )
                               end )
 
         @dictionary.add_word( ['sign'],
@@ -205,15 +185,14 @@ module RplLang
                               '( a -- b ) sign of element',
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
-                                args[0].value = if args[0].value.positive?
-                                                  1
-                                                elsif args[0].value.negative?
-                                                  -1
-                                                else
-                                                  0
-                                                end
 
-                                @stack << args[0]
+                                @stack << RplNumeric.new( if args[0].value.positive?
+                                                            1
+                                                          elsif args[0].value.negative?
+                                                            -1
+                                                          else
+                                                            0
+                                                          end )
                               end )
 
         # Operations on reals
@@ -223,9 +202,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = args[0].value * ( args[1].value / 100.0 )
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[0].value * ( args[1].value / 100.0 ), args[1].base )
                               end )
 
         @dictionary.add_word( ['%CH'],
@@ -234,9 +211,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = 100.0 * ( args[0].value / args[1].value )
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( 100.0 * ( args[0].value / args[1].value ), args[1].base )
                               end )
 
         @dictionary.add_word( ['mod'],
@@ -245,9 +220,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric], [RplNumeric]] )
 
-                                args[1].value = args[1].value % args[0].value
-
-                                @stack << args[1]
+                                @stack << RplNumeric.new( args[1].value % args[0].value, args[1].base )
                               end )
 
         @dictionary.add_word( ['!', 'fact'],
@@ -256,9 +229,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = Math.gamma( args[0].value )
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( Math.gamma( args[0].value ), args[0].base )
                               end )
 
         @dictionary.add_word( ['floor'],
@@ -267,9 +238,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = args[0].value.floor
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( args[0].value.floor, args[0].base )
                               end )
 
         @dictionary.add_word( ['ceil'],
@@ -278,9 +247,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = args[0].value.ceil
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( args[0].value.ceil, args[0].base )
                               end )
 
         @dictionary.add_word( ['min'],
@@ -316,9 +283,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = args[0].value.exponent
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( args[0].value.exponent, args[0].base )
                               end )
 
         @dictionary.add_word( ['ip'],
@@ -334,9 +299,7 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplNumeric]] )
 
-                                args[0].value = args[0].value.frac
-
-                                @stack << args[0]
+                                @stack << RplNumeric.new( args[0].value.frac, args[0].base )
                               end )
 
         # Operations on complexes
diff --git a/lib/rpl/words/string-list.rb b/lib/rpl/words/string-list.rb
index 6c99d8a..3d70298 100644
--- a/lib/rpl/words/string-list.rb
+++ b/lib/rpl/words/string-list.rb
@@ -98,9 +98,11 @@ module RplLang
                               proc do
                                 args = stack_extract( [[RplString, RplList]] )
 
-                                args[0].value.reverse!
-
-                                @stack << args[0]
+                                if args[0].is_a?( RplString )
+                                  @stack << args[0].class.new( "\"#{args[0].value.reverse}\"" )
+                                else
+                                  @stack << args[0].class.new( "{ #{args[0].value.reverse.join(' ')} }" )
+                                end
                               end )
 
         @dictionary.add_word( ['split'],
diff --git a/spec/language_operations_spec.rb b/spec/language_operations_spec.rb
index e04754f..153d935 100644
--- a/spec/language_operations_spec.rb
+++ b/spec/language_operations_spec.rb
@@ -27,7 +27,7 @@ class TesttLanguageOperations < MiniTest::Test
     interpreter = Rpl.new
     interpreter.run '1 dup dup →list +'
     assert_equal [Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
-                                Types.new_object( RplNumeric, 1 )] )],
+                                              Types.new_object( RplNumeric, 1 )] )],
                  interpreter.stack
 
     interpreter = Rpl.new
@@ -48,7 +48,7 @@ class TesttLanguageOperations < MiniTest::Test
     interpreter = Rpl.new
     interpreter.run '"a" 1 dup →list +'
     assert_equal [Types.new_object( RplList, [Types.new_object( RplString, '"a"' ),
-                                Types.new_object( RplNumeric, 1 )] )],
+                                              Types.new_object( RplNumeric, 1 )] )],
                  interpreter.stack
 
     interpreter = Rpl.new
@@ -69,25 +69,144 @@ class TesttLanguageOperations < MiniTest::Test
     interpreter = Rpl.new
     interpreter.run '\'a\' 1 dup →list +'
     assert_equal [Types.new_object( RplList, [Types.new_object( RplName, 'a' ),
-                                Types.new_object( RplNumeric, 1 )] )],
+                                              Types.new_object( RplNumeric, 1 )] )],
                  interpreter.stack
 
     interpreter = Rpl.new
     interpreter.run '1 a "test" 3 →list dup rev +'
     assert_equal [Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
-                                Types.new_object( RplName, 'a' ),
-                                Types.new_object( RplString, '"test"' ),
-                                Types.new_object( RplString, '"test"' ),
-                                Types.new_object( RplName, 'a' ),
-                                Types.new_object( RplNumeric, 1 )] )],
+                                              Types.new_object( RplName, 'a' ),
+                                              Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplName, 'a' ),
+                                              Types.new_object( RplNumeric, 1 )] )],
                  interpreter.stack
 
     interpreter = Rpl.new
     interpreter.run '1 a "test" 3 →list 9 +'
     assert_equal [Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
-                                Types.new_object( RplName, 'a' ),
-                                Types.new_object( RplString, '"test"' ),
-                                Types.new_object( RplNumeric, 9 )] )],
+                                              Types.new_object( RplName, 'a' ),
+                                              Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplNumeric, 9 )] )],
+                 interpreter.stack
+
+    #################
+    # now with vars #
+    #################
+
+    interpreter = Rpl.new
+    interpreter.run '1 \'a\' sto 2 \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplNumeric, 3 ),
+                  Types.new_object( RplNumeric, 1 ),
+                  Types.new_object( RplNumeric, 2 )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '1 \'a\' sto "a" \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplString, '"1a"' ),
+                  Types.new_object( RplNumeric, 1 ),
+                  Types.new_object( RplString, '"a"' )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '1 \'a\' sto \'z\' \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplName, "'1z'" ),
+                  Types.new_object( RplNumeric, 1 ),
+                  Types.new_object( RplName, "'z'" )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '1 \'a\' sto a dup →list \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
+                                              Types.new_object( RplNumeric, 1 )] ),
+                  Types.new_object( RplNumeric, 1 ),
+                  Types.new_object( RplList, [Types.new_object( RplNumeric, 1 )] )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '"a" \'a\' sto "b" \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplString, '"ab"' ),
+                  Types.new_object( RplString, '"a"' ),
+                  Types.new_object( RplString, '"b"' )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '"a" \'a\' sto \'z\' \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplString, '"az"' ),
+                  Types.new_object( RplString, '"a"' ),
+                  Types.new_object( RplName, "'z'" )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '"a" \'a\' sto 1 \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplString, '"a1"' ),
+                  Types.new_object( RplString, '"a"' ),
+                  Types.new_object( RplNumeric, 1 )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '"a" \'a\' sto 1 dup →list \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplList, [Types.new_object( RplString, '"a"' ),
+                                              Types.new_object( RplNumeric, 1 )] ),
+                  Types.new_object( RplString, '"a"' ),
+                  Types.new_object( RplList, [Types.new_object( RplNumeric, 1 )] )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '\'z\' \'a\' sto 1 \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplName, 'z1' ),
+                  Types.new_object( RplName, 'z' ),
+                  Types.new_object( RplNumeric, 1 )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '\'z\' \'a\' sto "b" \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplString, '"zb"' ),
+                  Types.new_object( RplName, "'z'" ),
+                  Types.new_object( RplString, '"b"' )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '\'z\' \'a\' sto \'y\' \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplName, "'zy'" ),
+                  Types.new_object( RplName, "'z'" ),
+                  Types.new_object( RplName, "'y'" )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '\'z\' \'a\' sto 1 dup →list \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplList, [Types.new_object( RplName, "'z'" ),
+                                              Types.new_object( RplNumeric, 1 )] ),
+                  Types.new_object( RplName, "'z'" ),
+                  Types.new_object( RplList, [Types.new_object( RplNumeric, 1 )] )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '1 z "test" 3 →list \'a\' sto a rev \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
+                                              Types.new_object( RplName, 'z' ),
+                                              Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplName, 'z' ),
+                                              Types.new_object( RplNumeric, 1 )] ),
+                  Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
+                                              Types.new_object( RplName, 'z' ),
+                                              Types.new_object( RplString, '"test"' )] ),
+                  Types.new_object( RplList, [Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplName, 'z' ),
+                                              Types.new_object( RplNumeric, 1 )] )],
+                 interpreter.stack
+
+    interpreter = Rpl.new
+    interpreter.run '1 a "test" 3 →list \'a\' sto 9 \'b\' sto a b + a b'
+    assert_equal [Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
+                                              Types.new_object( RplName, 'a' ),
+                                              Types.new_object( RplString, '"test"' ),
+                                              Types.new_object( RplNumeric, 9 )] ),
+                  Types.new_object( RplList, [Types.new_object( RplNumeric, 1 ),
+                                              Types.new_object( RplName, 'a' ),
+                                              Types.new_object( RplString, '"test"' )] ),
+                  Types.new_object( RplNumeric, 9 )],
                  interpreter.stack
   end