diff --git a/gcc/elna-generic.cc b/gcc/elna-generic.cc
index 35e451a..95b8603 100644
--- a/gcc/elna-generic.cc
+++ b/gcc/elna-generic.cc
@@ -303,24 +303,26 @@ namespace gcc
     void generic_visitor::visit(boot::binary_expression *expression)
     {
         expression->lhs().accept(this);
-        auto left = this->current_expression;
-        auto left_type = TREE_TYPE(left);
+        tree left = this->current_expression;
+        tree left_type = TREE_TYPE(left);
 
         expression->rhs().accept(this);
-        auto right = this->current_expression;
-        auto right_type = TREE_TYPE(right);
+        tree right = this->current_expression;
+        tree right_type = TREE_TYPE(right);
 
-        auto expression_location = get_location(&expression->position());
+        location_t expression_location = get_location(&expression->position());
         tree_code operator_code = ERROR_MARK;
         tree target_type = error_mark_node;
 
-        if (is_pointer_type(left_type) && is_integral_type(right_type)
-                && expression->operation() == boot::binary_operator::sum)
+        if (is_pointer_type(left_type) && is_integral_type(right_type))
         {
-            tree convert_expression = build1_loc(expression_location, CONVERT_EXPR,
-                    sizetype, right);
-            this->current_expression = build2_loc(expression_location,
-                    POINTER_PLUS_EXPR, left_type, left, convert_expression);
+            this->current_expression = do_pointer_arithmetic(expression->operation(), left, right);
+            if (this->current_expression == error_mark_node)
+            {
+                error_at(expression_location,
+                        "invalid operation %s on a pointer and an integral type",
+                        boot::print_binary_operator(expression->operation()));
+            }
             return;
         }
         if (left_type != right_type)
diff --git a/gcc/elna-tree.cc b/gcc/elna-tree.cc
index 56d916c..4df2806 100644
--- a/gcc/elna-tree.cc
+++ b/gcc/elna-tree.cc
@@ -1,6 +1,7 @@
 #include "elna/gcc/elna-tree.h"
 
 #include "stor-layout.h"
+#include "fold-const.h"
 
 tree elna_global_trees[ELNA_TI_MAX];
 
@@ -81,5 +82,22 @@ namespace gcc
 
         return initial_table;
     }
+
+    tree do_pointer_arithmetic(boot::binary_operator binary_operator, tree left, tree right)
+    {
+        tree result = error_mark_node;
+        tree convert_expression = fold_convert(sizetype, right);
+
+        if (binary_operator == boot::binary_operator::sum)
+        {
+            result = fold_build2(POINTER_PLUS_EXPR, TREE_TYPE(left), left, convert_expression);
+        }
+        else if (binary_operator == boot::binary_operator::subtraction)
+        {
+            convert_expression = fold_build1(NEGATE_EXPR, sizetype, convert_expression);
+            result = fold_build2(POINTER_PLUS_EXPR, TREE_TYPE(left), left, convert_expression);
+        }
+        return result;
+    }
 }
 }
diff --git a/include/elna/gcc/elna-tree.h b/include/elna/gcc/elna-tree.h
index dada145..def424e 100644
--- a/include/elna/gcc/elna-tree.h
+++ b/include/elna/gcc/elna-tree.h
@@ -4,8 +4,8 @@
 #include "system.h"
 #include "coretypes.h"
 #include "tree.h"
-#include "tree.h"
 
+#include "elna/boot/ast.h"
 #include "elna/boot/symbol.h"
 
 enum elna_tree_index
@@ -58,5 +58,7 @@ namespace gcc
     };
 
     std::shared_ptr<boot::symbol_table<tree>> builtin_symbol_table();
+
+    tree do_pointer_arithmetic(boot::binary_operator binary_operator, tree left, tree right);
 }
 }
diff --git a/source.elna b/source.elna
index c53c785..bd15e59 100644
--- a/source.elna
+++ b/source.elna
@@ -20,6 +20,9 @@ type
   end,
   FILE = record
     dummy: Int
+  end,
+  CommandLine = record
+    input: pointer to Char
   end;
 
 const
@@ -141,19 +144,6 @@ end;
   End of standard procedures.
 *)
 
-proc test_primitive();
-begin
-  write_s("\nTest primitives:\n");
-  write_u(25u);
-  write_c('\n');
-
-  write_i(8);
-  write_c('\n');
-
-  write_b(true);
-  write_c('\n')
-end;
-
 proc read_source(filename: String): pointer to Char;
 var
   input_file: pointer to FILE,
@@ -272,7 +262,7 @@ var
   is_valid: Bool;
 begin
   token_end := input;
-  previous := cast(cast(input as Word) - 1u as pointer to Char);
+  previous := input - 1;
 
   while token_end^ <> '\0' and not (previous^ <> '\\' and token_end^ = '"') do
     previous := token_end;
@@ -677,32 +667,51 @@ begin
   return tokens
 end;
 
-proc command_line(argc: Int, argv: pointer to pointer to Char);
+proc parse_command_line(argc: Int, argv: pointer to pointer to Char): pointer to CommandLine;
 var
   parameter: pointer to pointer to Char,
-  i: Int;
+  i: Int,
+  result: pointer to CommandLine;
 begin
-  write_s("Argument count: ");
-  write_i(argc - 1);
-  write_s("\nArguments:");
+  if argc < 2 then
+    write_s("Fatal error: no input files.\n");
+	return nil
+  end;
+  if argc > 2 then
+    write_s("Fatal error: Unknown command line options:");
 
-  i := 1;
-  while i < argc do
-    parameter := argv + i * cast(sizeof(pointer to Char) as Int);
+    i := 2;
+    while i < argc do
+      parameter := argv + i * cast(sizeof(pointer to Char) as Int);
+ 
+      write_c(' ');
+      write_s(parameter^);
+      i := i + 1
+    end;
+	write_s(".\n");
+	return nil
+  end;
 
-	write_c(' ');
-    write_s(parameter^);
-    i := i + 1
-  end
+  parameter := argv + cast(sizeof(pointer to Char) as Int);
+  result := cast(malloc(sizeof(CommandLine)) as pointer to CommandLine);
+  result^.input := parameter^;
+
+  return result
 end;
 
-proc compile();
+proc process(argc: Int, argv: pointer to pointer to Char): Int;
 var
   input: pointer to Char,
   tokens: pointer to Token,
-  tokens_size: Word;
+  tokens_size: Word,
+  command_line: pointer to CommandLine;
 begin
-  input := read_source("example.elna");
+  command_line := parse_command_line(argc, argv);
+
+  if cast(command_line as Word) = 0u then
+    return 2
+  end;
+  input := read_source(command_line^.input);
   tokens := tokenize(input, @tokens_size);
 
   free(input);
@@ -711,9 +720,5 @@ begin
 end;
 
 begin
-  command_line(count, parameters);
-  compile();
-  test_primitive();
-
-  exit(0)
+  exit(process(count, parameters))
 end.