diff --git a/boot/lexer.ll b/boot/lexer.ll
index 4039fea..f0bbe8a 100644
--- a/boot/lexer.ll
+++ b/boot/lexer.ll
@@ -262,6 +262,9 @@ defer                   {
 \+                      {
                             return yy::parser::make_PLUS(this->location);
                         }
+\->                     {
+                            return yy::parser::make_ARROW(this->location);
+                        }
 \-                      {
                             return yy::parser::make_MINUS(this->location);
                         }
diff --git a/boot/parser.yy b/boot/parser.yy
index f1233f5..e4824cb 100644
--- a/boot/parser.yy
+++ b/boot/parser.yy
@@ -88,7 +88,7 @@ along with GCC; see the file COPYING3.  If not see
 %token AND OR NOT CAST AS SIZEOF
 %token GREATER_EQUAL LESS_EQUAL LESS_THAN GREATER_THAN NOT_EQUAL EQUALS
 %token PLUS MINUS MULTIPLICATION DIVISION REMAINDER
-%token ASSIGNMENT COLON HAT AT NIL
+%token ASSIGNMENT COLON HAT AT NIL ARROW
 
 %left OR AND
 %left EQUALS NOT_EQUAL LESS_THAN GREATER_THAN LESS_EQUAL GREATER_EQUAL
@@ -161,7 +161,7 @@ procedure_heading:
                  $2.first, $2.second);
             std::swap($3, $$->parameters);
         }
-    | PROCEDURE identifier_definition formal_parameter_list COLON type_expression SEMICOLON
+    | PROCEDURE identifier_definition formal_parameter_list ARROW type_expression SEMICOLON
         {
             $$ = new elna::boot::procedure_definition(elna::boot::make_position(@1),
                  $2.first, $2.second, $5);
diff --git a/gcc/elna-builtins.cc b/gcc/elna-builtins.cc
index a2e6ee0..3c2de3f 100644
--- a/gcc/elna-builtins.cc
+++ b/gcc/elna-builtins.cc
@@ -30,10 +30,15 @@ namespace gcc
         elna_int_type_node = long_integer_type_node;
         elna_word_type_node = size_type_node;
         elna_char_type_node = unsigned_char_type_node;
-        elna_bool_type_node = boolean_type_node;
         elna_byte_type_node = make_unsigned_type(8);
         elna_float_type_node = double_type_node;
 
+        elna_bool_type_node = boolean_type_node;
+        elna_bool_true_node = boolean_true_node;
+        elna_bool_false_node = boolean_false_node;
+
+        elna_pointer_nil_node = null_pointer_node;
+
         elna_string_type_node = make_node(RECORD_TYPE);
         tree string_ptr_type = build_pointer_type_for_mode(elna_char_type_node, VOIDmode, true);
         tree record_chain = NULL_TREE;
diff --git a/gcc/elna-generic.cc b/gcc/elna-generic.cc
index 4739f29..ae29817 100644
--- a/gcc/elna-generic.cc
+++ b/gcc/elna-generic.cc
@@ -323,7 +323,7 @@ namespace gcc
 
     void generic_visitor::visit(boot::number_literal<bool> *boolean)
     {
-        this->current_expression = build_int_cst_type(elna_bool_type_node, boolean->number());
+        this->current_expression = boolean->number() ? boolean_true_node : boolean_false_node;
     }
 
     void generic_visitor::visit(boot::number_literal<unsigned char> *character)
@@ -333,7 +333,7 @@ namespace gcc
 
     void generic_visitor::visit(boot::number_literal<nullptr_t> *)
     {
-        this->current_expression = null_pointer_node;
+        this->current_expression = elna_pointer_nil_node;
     }
 
     void generic_visitor::visit(boot::number_literal<std::string> *string)
diff --git a/gcc/elna-tree.cc b/gcc/elna-tree.cc
index 300a9cf..5613724 100644
--- a/gcc/elna-tree.cc
+++ b/gcc/elna-tree.cc
@@ -50,7 +50,7 @@ namespace gcc
         tree lhs_type = TREE_TYPE(lhs);
         tree rhs_type = TREE_TYPE(rhs);
 
-        return (is_pointer_type(lhs_type) && rhs == null_pointer_node)
+        return (is_pointer_type(lhs_type) && rhs == elna_pointer_nil_node)
             || (is_pointer_type(lhs_type) && lhs_type == rhs_type);
     }
 
diff --git a/include/elna/gcc/elna1.h b/include/elna/gcc/elna1.h
index 93d0043..f4f86f5 100644
--- a/include/elna/gcc/elna1.h
+++ b/include/elna/gcc/elna1.h
@@ -24,6 +24,9 @@ enum elna_tree_index
     ELNA_TI_BYTE_TYPE,
     ELNA_TI_FLOAT_TYPE,
     ELNA_TI_STRING_TYPE,
+    ELNA_TI_BOOL_TRUE,
+    ELNA_TI_BOOL_FALSE,
+    ELNA_TI_POINTER_NIL,
     ELNA_TI_MAX
 };
 
@@ -37,6 +40,9 @@ extern GTY(()) hash_map<nofree_string_hash, tree> *elna_global_decls;
 #define elna_byte_type_node elna_global_trees[ELNA_TI_BYTE_TYPE]
 #define elna_float_type_node elna_global_trees[ELNA_TI_FLOAT_TYPE]
 #define elna_string_type_node elna_global_trees[ELNA_TI_STRING_TYPE]
+#define elna_bool_true_node elna_global_trees[ELNA_TI_BOOL_TRUE]
+#define elna_bool_false_node elna_global_trees[ELNA_TI_BOOL_FALSE]
+#define elna_pointer_nil_node elna_global_trees[ELNA_TI_POINTER_NIL]
 
 /* Language-dependent contents of a type. */
 struct GTY (()) lang_type
diff --git a/source.elna b/source.elna
index b069d86..2a08830 100644
--- a/source.elna
+++ b/source.elna
@@ -67,28 +67,28 @@ type
 (*
   External procedures.
 *)
-proc fopen(pathname: pointer to Char, mode: pointer to Char): pointer to FILE; extern
-proc fclose(stream: pointer to FILE): Int; extern
-proc fseek(stream: pointer to FILE, off: Int, whence: Int): Int; extern
+proc fopen(pathname: pointer to Char, mode: pointer to Char) -> pointer to FILE; extern
+proc fclose(stream: pointer to FILE) -> Int; extern
+proc fseek(stream: pointer to FILE, off: Int, whence: Int) -> Int; extern
 proc rewind(stream: pointer to FILE); extern
-proc ftell(stream: pointer to FILE): Int; extern
-proc fread(ptr: pointer to Byte, size: Word, nmemb: Word, stream: pointer to FILE): Word; extern
-proc write(fd: Int, buf: pointer to Byte, Word: Int): Int; extern
+proc ftell(stream: pointer to FILE) -> Int; extern
+proc fread(ptr: pointer to Byte, size: Word, nmemb: Word, stream: pointer to FILE) -> Word; extern
+proc write(fd: Int, buf: pointer to Byte, Word: Int) -> Int; extern
 
-proc malloc(size: Word): pointer to Byte; extern
+proc malloc(size: Word) -> pointer to Byte; extern
 proc free(ptr: pointer to Byte); extern
-proc calloc(nmemb: Word, size: Word): pointer to Byte; extern
-proc realloc(ptr: pointer to Byte, size: Word): pointer to Byte; extern
+proc calloc(nmemb: Word, size: Word) -> pointer to Byte; extern
+proc realloc(ptr: pointer to Byte, size: Word) -> pointer to Byte; extern
 
-proc memset(ptr: pointer to Char, c: Int, n: Int): pointer to Char; extern
+proc memset(ptr: pointer to Char, c: Int, n: Int) -> pointer to Char; extern
 
-proc strcmp(s1: pointer to Char, s2: pointer to Char): Int; extern
-proc strncmp(s1: pointer to Char, s2: pointer to Char, n: Word): Int; extern
-proc strncpy(dst: pointer to Char, src: pointer to Char, dsize: Word): pointer to Char; extern
-proc strcpy(dst: pointer to Char, src: pointer to Char): pointer to Char; extern
-proc strlen(ptr: pointer to Char): Word; extern
+proc strcmp(s1: pointer to Char, s2: pointer to Char) -> Int; extern
+proc strncmp(s1: pointer to Char, s2: pointer to Char, n: Word) -> Int; extern
+proc strncpy(dst: pointer to Char, src: pointer to Char, dsize: Word) -> pointer to Char; extern
+proc strcpy(dst: pointer to Char, src: pointer to Char) -> pointer to Char; extern
+proc strlen(ptr: pointer to Char) -> Word; extern
 
-proc strtol(nptr: pointer to Char, endptr: pointer to pointer to Char, base: Int): Int; extern
+proc strtol(nptr: pointer to Char, endptr: pointer to pointer to Char, base: Int) -> Int; extern
 
 proc perror(s: pointer to Char); extern
 proc exit(code: Int); extern
@@ -96,7 +96,7 @@ proc exit(code: Int); extern
 (*
   Standard procedures.
 *)
-proc reallocarray(ptr: pointer to Byte, n: Word, size: Word): pointer to Byte;
+proc reallocarray(ptr: pointer to Byte, n: Word, size: Word) -> pointer to Byte;
 begin
   return realloc(ptr, n * size)
 end
@@ -154,40 +154,40 @@ begin
   write_i(value)
 end
 
-proc is_digit(c: Char): Bool;
+proc is_digit(c: Char) -> Bool;
 begin
   return cast(c as Int) >= cast('0' as Int) and cast(c as Int) <= cast('9' as Int)
 end
 
-proc is_alpha(c: Char): Bool;
+proc is_alpha(c: Char) -> Bool;
 begin
   return cast(c as Int) >= cast('A' as Int) and cast(c as Int) <= cast('z' as Int)
 end
 
-proc is_alnum(c: Char): Bool;
+proc is_alnum(c: Char) -> Bool;
 begin
   return is_digit(c) or is_alpha(c)
 end
 
-proc is_space(c: Char): Bool;
+proc is_space(c: Char) -> Bool;
 begin
   return c = ' ' or c = '\n' or c = '\t'
 end
 
-proc open_substring(string: String, start: Word): String;
+proc open_substring(string: String, start: Word) -> String;
 begin
   string.ptr := string.ptr + start;
   string.length := string.length - start;
   return string
 end
 
-proc substring(string: String, start: Word, count: Word): String;
+proc substring(string: String, start: Word, count: Word) -> String;
 begin
   string.ptr := string.ptr + start;
   string.length := count
 end
 
-proc string_dup(origin: String): String;
+proc string_dup(origin: String) -> String;
 var
   copy: pointer to Char;
 begin
@@ -198,7 +198,7 @@ begin
   return origin
 end
 
-proc char_at(string: String, position: Word): Char;
+proc char_at(string: String, position: Word) -> Char;
 begin
   return (string.ptr + position)^
 end
@@ -207,7 +207,7 @@ end
   End of standard procedures.
 *)
 
-proc make_position(): Position;
+proc make_position() -> Position;
 var
   result: Position;
 begin
@@ -216,7 +216,7 @@ begin
   return result
 end
 
-proc read_source(filename: pointer to Char, result: pointer to String): Bool;
+proc read_source(filename: pointer to Char, result: pointer to String) -> Bool;
 var
   input_file: pointer to FILE,
   source_size: Int,
@@ -249,7 +249,7 @@ begin
   return true
 end
 
-proc escape_char(escape: Char, result: pointer to Char): Bool;
+proc escape_char(escape: Char, result: pointer to Char) -> Bool;
 begin
   if escape = 'n' then
 	result^ := '\n';
@@ -292,7 +292,7 @@ begin
   end
 end
 
-proc advance_source(source_code: SourceCode, length: Word): SourceCode;
+proc advance_source(source_code: SourceCode, length: Word) -> SourceCode;
 begin
   source_code.text := open_substring(source_code.text, length);
   source_code.position.column := source_code.position.column + length;
@@ -300,7 +300,7 @@ begin
   return source_code
 end
 
-proc skip_spaces(source_code: SourceCode): SourceCode;
+proc skip_spaces(source_code: SourceCode) -> SourceCode;
 begin
   while source_code.text.length > 0u and is_space(char_at(source_code.text, 0)) do
     if char_at(source_code.text, 0) = '\n' then
@@ -328,7 +328,7 @@ begin
   token_content^ := substring(token_content^, 0u, content_length)
 end
 
-proc lex_comment(source_code: pointer to SourceCode, token_content: pointer to String): Bool;
+proc lex_comment(source_code: pointer to SourceCode, token_content: pointer to String) -> Bool;
 var
   content_length: Word;
 begin
@@ -349,7 +349,7 @@ begin
   return false
 end
 
-proc lex_character(input: pointer to Char, current_token: pointer to Token): pointer to Char;
+proc lex_character(input: pointer to Char, current_token: pointer to Token) -> pointer to Char;
 begin
   if input^ = '\\' then
     input := input + 1;
@@ -363,7 +363,7 @@ begin
   return input
 end
 
-proc lex_string(input: pointer to Char, current_token: pointer to Token): pointer to Char;
+proc lex_string(input: pointer to Char, current_token: pointer to Token) -> pointer to Char;
 var
   token_end: pointer to Char,
   constructed_string: pointer to Char,
@@ -548,7 +548,7 @@ begin
   write_c('\n')
 end
 
-proc categorize_identifier(token_content: String): Token;
+proc categorize_identifier(token_content: String) -> Token;
 var
   current_token: Token;
 begin
@@ -622,7 +622,7 @@ begin
   return current_token
 end
 
-proc tokenize(source_code: SourceCode, tokens_size: pointer to Word): pointer to Token;
+proc tokenize(source_code: SourceCode, tokens_size: pointer to Word) -> pointer to Token;
 var
   token_end: pointer to Char,
   tokens: pointer to Token,
@@ -786,13 +786,13 @@ begin
   return tokens
 end
 
-proc parse_literal(tokens: pointer to pointer to Token, tokens_size: pointer to Word): pointer to Literal;
+proc parse_literal(tokens: pointer to pointer to Token, tokens_size: pointer to Word) -> pointer to Literal;
 begin
   return cast(calloc(1, sizeof(Literal)) as pointer to Literal)
 end
 
 proc parse_constant_definition(tokens: pointer to pointer to Token,
-    tokens_size: pointer to Word): pointer to ConstantDefinition;
+    tokens_size: pointer to Word) -> pointer to ConstantDefinition;
 var
   result: pointer to ConstantDefinition;
 begin
@@ -815,7 +815,7 @@ begin
   return result
 end
 
-proc parse_program(tokens: pointer to pointer to Token, tokens_size: pointer to Word): pointer to Program;
+proc parse_program(tokens: pointer to pointer to Token, tokens_size: pointer to Word) -> pointer to Program;
 var
   result: pointer to Program,
   current_constant: pointer to pointer to ConstantDefinition;
@@ -845,7 +845,7 @@ begin
   end
 end
 
-proc parse_command_line*(argc: Int, argv: pointer to pointer to Char): pointer to CommandLine;
+proc parse_command_line*(argc: Int, argv: pointer to pointer to Char) -> pointer to CommandLine;
 var
   parameter: pointer to pointer to Char,
   i: Int,
@@ -886,7 +886,7 @@ begin
   return result
 end
 
-proc process(argc: Int, argv: pointer to pointer to Char): Int;
+proc process(argc: Int, argv: pointer to pointer to Char) -> Int;
 var
   tokens: pointer to Token,
   tokens_size: Word,