X-Git-Url: https://deadsoftware.ru/gitweb?p=dsw-obn.git;a=blobdiff_plain;f=src%2Foberon.c;h=ece881fc44366290a324ac54b55def84b1c9804b;hp=58eb67c3eb72562294074f972fde2e15f68b5fec;hb=49ad3c76fc9656759aab23d9034ebc33f8d8bd9d;hpb=55d9ee92b95dd306ac80fb643ed21d3b733395d7

diff --git a/src/oberon.c b/src/oberon.c
index 58eb67c..ece881f 100644
--- a/src/oberon.c
+++ b/src/oberon.c
@@ -24,8 +24,6 @@ enum {
 	BEGIN,
 	ASSIGN,
 	INTEGER,
-	TRUE,
-	FALSE,
 	LPAREN,
 	RPAREN,
 	EQUAL,
@@ -344,14 +342,6 @@ oberon_read_ident(oberon_context_t * ctx)
 	{
 		ctx -> token = BEGIN;
 	}
-	else if(strcmp(ident, "TRUE") == 0)
-	{
-		ctx -> token = TRUE;
-	}
-	else if(strcmp(ident, "FALSE") == 0)
-	{
-		ctx -> token = FALSE;
-	}
 	else if(strcmp(ident, "OR") == 0)
 	{
 		ctx -> token = OR;
@@ -474,6 +464,9 @@ oberon_read_ident(oberon_context_t * ctx)
 	}
 }
 
+#define ISHEXDIGIT(x) \
+	(((x) >= '0' && (x) <= '9') || ((x) >= 'A' && (x) <= 'F'))
+
 static void
 oberon_read_number(oberon_context_t * ctx)
 {
@@ -501,10 +494,10 @@ oberon_read_number(oberon_context_t * ctx)
 
 	end_i = ctx -> code_index;
 
-	if(isxdigit(ctx -> c))
+	if(ISHEXDIGIT(ctx -> c))
 	{
 		mode = 1;
-		while(isxdigit(ctx -> c))
+		while(ISHEXDIGIT(ctx -> c))
 		{
 			oberon_get_char(ctx);
 		}
@@ -697,8 +690,6 @@ static void oberon_read_string(oberon_context_t * ctx)
 
 	ctx -> token = STRING;
 	ctx -> string = string;
-
-	printf("oberon_read_string: string ((%s))\n", string);
 }
 
 static void oberon_read_token(oberon_context_t * ctx);
@@ -993,11 +984,8 @@ oberno_make_record_cast(oberon_context_t * ctx, oberon_expr_t * expr, oberon_typ
 	oberon_type_t * from = expr -> result;
 	oberon_type_t * to = rec;
 
-	printf("oberno_make_record_cast: from class %i to class %i\n", from -> class, to -> class);
-
 	if(from -> class == OBERON_TYPE_POINTER && to -> class == OBERON_TYPE_POINTER)
 	{
-		printf("oberno_make_record_cast: pointers\n");
 		from = from -> base;
 		to = to -> base;
 	}
@@ -1106,19 +1094,41 @@ oberon_autocast_to(oberon_context_t * ctx, oberon_expr_t * expr, oberon_type_t *
 	// Допускается:
 	//  Если классы типов равны
 	//  Если INTEGER переводится в REAL
-	//  Есди STRING переводится в ARRAY OF CHAR
+	//  Если STRING переводится в CHAR
+	//  Если STRING переводится в ARRAY OF CHAR
+	//  Если NIL переводится в POINTER
+	//  Если NIL переводится в PROCEDURE
 
 	oberon_check_src(ctx, expr);
 
 	bool error = false;
 	if(pref -> class != expr -> result -> class)
 	{
-		printf("expr class %i\n", expr -> result -> class);
-		printf("pref class %i\n", pref -> class);
-
-		if(expr -> result -> class == OBERON_TYPE_STRING)
+		if(expr -> result -> class == OBERON_TYPE_NIL)
+		{
+			if(pref -> class != OBERON_TYPE_POINTER
+				&& pref -> class != OBERON_TYPE_PROCEDURE)
+			{
+				error = true;
+			}
+		}
+		else if(expr -> result -> class == OBERON_TYPE_STRING)
 		{
-			if(pref -> class == OBERON_TYPE_ARRAY)
+			if(pref -> class == OBERON_TYPE_CHAR)
+			{
+				if(expr -> is_item && expr -> item.mode == MODE_STRING)
+				{
+					if(strlen(expr -> item.string) != 1)
+					{
+						error = true;
+					}
+				}
+				else
+				{
+					error = true;
+				}
+			}
+			else if(pref -> class == OBERON_TYPE_ARRAY)
 			{
 				if(pref -> base -> class != OBERON_TYPE_CHAR)
 				{
@@ -1148,7 +1158,16 @@ oberon_autocast_to(oberon_context_t * ctx, oberon_expr_t * expr, oberon_type_t *
 		oberon_error(ctx, "oberon_autocast_to: incompatible types");
 	}
 
-	if(pref -> class == OBERON_TYPE_INTEGER || pref -> class == OBERON_TYPE_REAL)
+	if(pref -> class == OBERON_TYPE_CHAR)
+	{
+		if(expr -> result -> class == OBERON_TYPE_STRING)
+		{
+			int c = expr -> item.string[0];
+			expr = oberon_new_item(MODE_CHAR, ctx -> char_type, true);
+			expr -> item.integer = c;
+		}
+	}
+	else if(pref -> class == OBERON_TYPE_INTEGER || pref -> class == OBERON_TYPE_REAL)
 	{
 		if(expr -> result -> size > pref -> size)
 		{
@@ -1167,17 +1186,18 @@ oberon_autocast_to(oberon_context_t * ctx, oberon_expr_t * expr, oberon_type_t *
 	else if(pref -> class == OBERON_TYPE_POINTER)
 	{
 		assert(pref -> base);
-		if(expr -> result -> base -> class == OBERON_TYPE_RECORD)
+		if(expr -> result -> class == OBERON_TYPE_NIL)
+		{
+			// do nothing
+		}
+		else if(expr -> result -> base -> class == OBERON_TYPE_RECORD)
 		{
 			oberon_check_record_compatibility(ctx, expr -> result, pref);
 			expr = oberno_make_record_cast(ctx, expr, pref);
 		}
 		else if(expr -> result -> base != pref -> base)
 		{
-			if(expr -> result -> base -> class != OBERON_TYPE_VOID)
-			{
-				oberon_error(ctx, "incompatible pointer types");
-			}
+			oberon_error(ctx, "incompatible pointer types");
 		}
 	}
 
@@ -1276,7 +1296,7 @@ oberon_make_call_func(oberon_context_t * ctx, oberon_item_t * item, int num_args
 	}
 	else
 	{
-		if(signature -> base -> class == OBERON_TYPE_VOID)
+		if(signature -> base -> class == OBERON_TYPE_NOTYPE)
 		{
 			oberon_error(ctx, "attempt to call procedure in expression");
 		}
@@ -1313,7 +1333,7 @@ oberon_make_call_proc(oberon_context_t * ctx, oberon_item_t * item, int num_args
 	}
 	else
 	{
-		if(signature -> base -> class != OBERON_TYPE_VOID)
+		if(signature -> base -> class != OBERON_TYPE_NOTYPE)
 		{
 			oberon_error(ctx, "attempt to call function as non-typed procedure");
 		}
@@ -1337,14 +1357,11 @@ oberon_make_call_proc(oberon_context_t * ctx, oberon_item_t * item, int num_args
 	|| ((x) == STRING) \
 	|| ((x) == NIL) \
 	|| ((x) == LPAREN) \
-	|| ((x) == NOT) \
-	|| ((x) == TRUE) \
-	|| ((x) == FALSE)) 
+	|| ((x) == NOT))
 
 static oberon_expr_t *
 oberno_make_dereferencing(oberon_context_t * ctx, oberon_expr_t * expr)
 {
-	printf("oberno_make_dereferencing\n");
 	if(expr -> result -> class != OBERON_TYPE_POINTER)
 	{
 		oberon_error(ctx, "not a pointer");
@@ -1436,7 +1453,7 @@ oberon_make_record_selector(oberon_context_t * ctx, oberon_expr_t * expr, char *
 		}
 	}
 
-	int read_only = 0;
+	int read_only = expr -> read_only;
 	if(field -> read_only)
 	{
 		if(field -> module != ctx -> mod)
@@ -1556,11 +1573,46 @@ oberon_qualident_expr(oberon_context_t * ctx)
 	return expr;
 }
 
+static oberon_expr_t *
+oberon_make_type_guard(oberon_context_t * ctx, oberon_expr_t * expr, oberon_object_t * objtype)
+{
+	oberon_type_t * type;
+
+	if(objtype -> class != OBERON_CLASS_TYPE)
+	{
+		oberon_error(ctx, "must be type");
+	}
+	type = objtype -> type;
+
+	/* Охрана типа применима, если */
+	/*   1. v - параметр-переменная типа запись, или v - указатель, и если */
+	/*   2. T - расширение статического типа v */
+
+	if(expr -> is_item
+		&& expr -> item.mode == MODE_VAR
+		&& expr -> item.var -> class == OBERON_CLASS_VAR_PARAM)
+	{
+		// accept
+	}
+	else if(expr -> result -> class == OBERON_TYPE_POINTER)
+	{
+		// accept
+	}
+	else
+	{
+		oberon_error(ctx, "guard type used only with var-param or pointers");
+	}
+
+	oberon_check_record_compatibility(ctx, type, expr -> result);
+	return oberno_make_record_cast(ctx, expr, objtype -> type);
+}
+
 static oberon_expr_t *
 oberon_designator(oberon_context_t * ctx)
 {
 	char * name;
 	oberon_expr_t * expr;
+	oberon_object_t * objtype;
 
 	expr = oberon_qualident_expr(ctx);
 
@@ -1592,13 +1644,9 @@ oberon_designator(oberon_context_t * ctx)
 				break;
 			case LPAREN:
 				oberon_assert_token(ctx, LPAREN);
-				oberon_object_t * objtype = oberon_qualident(ctx, NULL, 1);
-				if(objtype -> class != OBERON_CLASS_TYPE)
-				{
-					oberon_error(ctx, "must be type");
-				}
+				objtype = oberon_qualident(ctx, NULL, true);
 				oberon_assert_token(ctx, RPAREN);
-				expr = oberno_make_record_cast(ctx, expr, objtype -> type);
+				expr = oberon_make_type_guard(ctx, expr, objtype);
 				break;
 			default:
 				oberon_error(ctx, "oberon_designator: wat");
@@ -1743,6 +1791,15 @@ oberon_set(oberon_context_t * ctx)
 	return set;
 }
 
+static oberon_expr_t *
+oberon_make_boolean(oberon_context_t * ctx, bool cond)
+{
+	oberon_expr_t * expr;
+	expr = oberon_new_item(MODE_BOOLEAN, ctx -> bool_type, true);
+	expr -> item.integer = cond;
+	return expr;
+}
+
 static oberon_expr_t *
 oberon_factor(oberon_context_t * ctx)
 {
@@ -1777,16 +1834,6 @@ oberon_factor(oberon_context_t * ctx)
 			expr -> item.real = ctx -> real;
 			oberon_assert_token(ctx, REAL);
 			break;
-		case TRUE:
-			expr = oberon_new_item(MODE_BOOLEAN, ctx -> bool_type, true);
-			expr -> item.boolean = true;
-			oberon_assert_token(ctx, TRUE);
-			break;
-		case FALSE:
-			expr = oberon_new_item(MODE_BOOLEAN, ctx -> bool_type, true);
-			expr -> item.boolean = false;
-			oberon_assert_token(ctx, FALSE);
-			break;
 		case LBRACE:
 			expr = oberon_set(ctx);
 			break;
@@ -1802,7 +1849,7 @@ oberon_factor(oberon_context_t * ctx)
 			break;
 		case NIL:
 			oberon_assert_token(ctx, NIL);
-			expr = oberon_new_item(MODE_NIL, ctx -> void_ptr_type, true);
+			expr = oberon_new_item(MODE_NIL, ctx -> nil_type, true);
 			break;
 		default:
 			oberon_error(ctx, "invalid expression");
@@ -2134,12 +2181,9 @@ oberon_expr(oberon_context_t * ctx)
 	return expr;
 }
 
-static oberon_item_t *
-oberon_const_expr(oberon_context_t * ctx)
+static void
+oberon_check_const(oberon_context_t * ctx, oberon_expr_t * expr)
 {
-	oberon_expr_t * expr;
-	expr = oberon_expr(ctx);
-
 	if(expr -> is_item == 0)
 	{
 		oberon_error(ctx, "const expression are required");
@@ -2160,7 +2204,14 @@ oberon_const_expr(oberon_context_t * ctx)
 			oberon_error(ctx, "const expression are required");
 			break;
 	}
+}
 
+static oberon_item_t *
+oberon_const_expr(oberon_context_t * ctx)
+{
+	oberon_expr_t * expr;
+	expr = oberon_expr(ctx);
+	oberon_check_const(ctx, expr);
 	return (oberon_item_t *) expr;
 }
 
@@ -2253,7 +2304,7 @@ oberon_var_decl(oberon_context_t * ctx)
 	int num;
 	oberon_object_t * list;
 	oberon_type_t * type;
-	type = oberon_new_type_ptr(OBERON_TYPE_VOID);
+	type = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 
 	oberon_ident_list(ctx, OBERON_CLASS_VAR, false, &num, &list);
 	oberon_assert_token(ctx, COLON);
@@ -2284,7 +2335,7 @@ oberon_fp_section(oberon_context_t * ctx, int * num_decl)
 	oberon_assert_token(ctx, COLON);
 
 	oberon_type_t * type;
-	type = oberon_new_type_ptr(OBERON_TYPE_VOID);
+	type = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 	oberon_type(ctx, &type);
 
 	oberon_object_t * param = list;
@@ -2339,7 +2390,7 @@ oberon_opt_formal_pars(oberon_context_t * ctx, oberon_type_t ** type)
 	signature = *type;
 	signature -> class = OBERON_TYPE_PROCEDURE;
 	signature -> num_decl = 0;
-	signature -> base = ctx -> void_type;
+	signature -> base = ctx -> notype_type;
 	signature -> decl = NULL;
 
 	if(ctx -> token == LPAREN)
@@ -2382,7 +2433,7 @@ oberon_make_return(oberon_context_t * ctx, oberon_expr_t * expr)
 	oberon_object_t * proc = ctx -> decl -> parent;
 	oberon_type_t * result_type = proc -> type -> base;
 
-	if(result_type -> class == OBERON_TYPE_VOID)
+	if(result_type -> class == OBERON_TYPE_NOTYPE)
 	{
 		if(expr != NULL)
 		{
@@ -2428,7 +2479,7 @@ oberon_proc_decl_body(oberon_context_t * ctx, oberon_object_t * proc)
 		oberon_error(ctx, "procedure name not matched");
 	}
 
-	if(proc -> type -> base -> class == OBERON_TYPE_VOID
+	if(proc -> type -> base -> class == OBERON_TYPE_NOTYPE
 		&& proc -> has_return == 0)
 	{
 		oberon_make_return(ctx, NULL);
@@ -2466,16 +2517,23 @@ oberon_proc_decl(oberon_context_t * ctx)
 	ctx -> decl -> local = 1;
 
 	oberon_type_t * signature;
-	signature = oberon_new_type_ptr(OBERON_TYPE_VOID);
+	signature = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 	oberon_opt_formal_pars(ctx, &signature);	
 
-	oberon_initialize_decl(ctx);
+	//oberon_initialize_decl(ctx);
 	oberon_generator_init_type(ctx, signature);
 	oberon_close_scope(ctx -> decl);
 
 	oberon_object_t * proc;
 	proc = oberon_find_object(ctx -> decl, name, 0);
-	if(proc != NULL)
+	if(proc == NULL)
+	{
+		proc = oberon_define_object(ctx -> decl, name, OBERON_CLASS_PROC, export, read_only, false);
+		proc -> type = signature;
+		proc -> scope = proc_scope;
+		oberon_generator_init_proc(ctx, proc);
+	}
+	else
 	{
 		if(proc -> class != OBERON_CLASS_PROC)
 		{
@@ -2497,16 +2555,15 @@ oberon_proc_decl(oberon_context_t * ctx)
 
 		oberon_compare_signatures(ctx, proc -> type, signature);
 	}
-	else
+
+	proc_scope -> parent = proc;
+	oberon_object_t * param = proc_scope -> list -> next;
+	while(param)
 	{
-		proc = oberon_define_object(ctx -> decl, name, OBERON_CLASS_PROC, export, read_only, false);
-		proc -> type = signature;
-		proc -> scope = proc_scope;
-		oberon_generator_init_proc(ctx, proc);
+		param -> parent = proc;
+		param = param -> next;
 	}
 
-	proc -> scope -> parent = proc;
-
 	if(forward == 0)
 	{
 		proc -> linked = 1;
@@ -2567,7 +2624,7 @@ oberon_qualident_type(oberon_context_t * ctx, oberon_type_t ** type)
 	else
 	{
 		to = oberon_define_object(ctx -> decl, name, OBERON_CLASS_TYPE, false, false, false);
-		to -> type = oberon_new_type_ptr(OBERON_TYPE_VOID);
+		to -> type = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 	}
 
 	*type = to -> type;
@@ -2589,7 +2646,7 @@ oberon_make_multiarray(oberon_context_t * ctx, oberon_expr_t * sizes, oberon_typ
 	}
 
 	oberon_type_t * dim;
-	dim = oberon_new_type_ptr(OBERON_TYPE_VOID);
+	dim = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 
 	oberon_make_multiarray(ctx, sizes -> next, base, &dim);
 
@@ -2612,7 +2669,7 @@ oberon_field_list(oberon_context_t * ctx, oberon_type_t * rec, oberon_scope_t *
 		int num;
 		oberon_object_t * list;
 		oberon_type_t * type;
-		type = oberon_new_type_ptr(OBERON_TYPE_VOID);
+		type = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 
 		oberon_ident_list(ctx, OBERON_CLASS_FIELD, true, &num, &list);
 		oberon_assert_token(ctx, COLON);
@@ -2713,7 +2770,7 @@ oberon_type(oberon_context_t * ctx, oberon_type_t ** type)
 		oberon_assert_token(ctx, OF);
 
 		oberon_type_t * base;
-		base = oberon_new_type_ptr(OBERON_TYPE_VOID);
+		base = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 		oberon_type(ctx, &base);
 
 		if(num_sizes == 0)
@@ -2744,7 +2801,7 @@ oberon_type(oberon_context_t * ctx, oberon_type_t ** type)
 		oberon_assert_token(ctx, TO);
 
 		oberon_type_t * base;
-		base = oberon_new_type_ptr(OBERON_TYPE_VOID);
+		base = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 		oberon_type(ctx, &base);
 
 		oberon_type_t * ptr;
@@ -2781,7 +2838,7 @@ oberon_type_decl(oberon_context_t * ctx)
 	if(newtype == NULL)
 	{
 		newtype = oberon_define_object(ctx -> decl, name, OBERON_CLASS_TYPE, export, read_only, false);
-		newtype -> type = oberon_new_type_ptr(OBERON_TYPE_VOID);
+		newtype -> type = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
 		assert(newtype -> type);
 	}
 	else
@@ -2805,7 +2862,7 @@ oberon_type_decl(oberon_context_t * ctx)
 	type = newtype -> type;
 	oberon_type(ctx, &type);
 
-	if(type -> class == OBERON_TYPE_VOID)
+	if(type -> class == OBERON_TYPE_NOTYPE)
 	{
 		oberon_error(ctx, "recursive alias declaration");
 	}
@@ -2859,6 +2916,11 @@ oberon_prevent_recursive_record(oberon_context_t * ctx, oberon_type_t * type)
 
 	type -> recursive = 1;
 
+	if(type -> base)
+	{
+		oberon_prevent_recursive_record(ctx, type -> base);
+	}
+
 	int num_fields = type -> num_decl;
 	oberon_object_t * field = type -> decl;
 	for(int i = 0; i < num_fields; i++)
@@ -3000,7 +3062,7 @@ oberon_initialize_record_fields(oberon_context_t * ctx, oberon_type_t * type)
 static void
 oberon_initialize_type(oberon_context_t * ctx, oberon_type_t * type)
 {
-	if(type -> class == OBERON_TYPE_VOID)
+	if(type -> class == OBERON_TYPE_NOTYPE)
 	{
 		oberon_error(ctx, "undeclarated type");
 	}
@@ -3701,7 +3763,7 @@ oberon_parse_module(oberon_context_t * ctx)
 
 	oberon_assert_token(ctx, END);
 	name2 = oberon_assert_ident(ctx);
-	oberon_assert_token(ctx, DOT);
+	oberon_expect_token(ctx, DOT);
 
 	if(strcmp(name1, name2) != 0)
 	{
@@ -3718,12 +3780,11 @@ oberon_parse_module(oberon_context_t * ctx)
 static void
 register_default_types(oberon_context_t * ctx)
 {
-	ctx -> void_type = oberon_new_type_ptr(OBERON_TYPE_VOID);
-	oberon_generator_init_type(ctx, ctx -> void_type);
+	ctx -> notype_type = oberon_new_type_ptr(OBERON_TYPE_NOTYPE);
+	oberon_generator_init_type(ctx, ctx -> notype_type);
 
-	ctx -> void_ptr_type = oberon_new_type_ptr(OBERON_TYPE_POINTER);
-	ctx -> void_ptr_type -> base = ctx -> void_type;
-	oberon_generator_init_type(ctx, ctx -> void_ptr_type);
+	ctx -> nil_type = oberon_new_type_ptr(OBERON_TYPE_NIL);
+	oberon_generator_init_type(ctx, ctx -> nil_type);
 
 	ctx -> string_type = oberon_new_type_string(1);
 	oberon_generator_init_type(ctx, ctx -> string_type);
@@ -3731,17 +3792,20 @@ register_default_types(oberon_context_t * ctx)
 	ctx -> bool_type = oberon_new_type_boolean();
 	oberon_define_type(ctx -> world_scope, "BOOLEAN", ctx -> bool_type, 1);
 
+	ctx -> char_type = oberon_new_type_char(1);
+	oberon_define_type(ctx -> world_scope, "CHAR", ctx -> char_type, 1);
+
 	ctx -> byte_type = oberon_new_type_integer(1);
-	oberon_define_type(ctx -> world_scope, "BYTE", ctx -> byte_type, 1);
+	oberon_define_type(ctx -> world_scope, "SHORTINT", ctx -> byte_type, 1);
 
 	ctx -> shortint_type = oberon_new_type_integer(2);
-	oberon_define_type(ctx -> world_scope, "SHORTINT", ctx -> shortint_type, 1);
+	oberon_define_type(ctx -> world_scope, "INTEGER", ctx -> shortint_type, 1);
 
 	ctx -> int_type = oberon_new_type_integer(4);
-	oberon_define_type(ctx -> world_scope, "INTEGER", ctx -> int_type, 1);
+	oberon_define_type(ctx -> world_scope, "LONGINT", ctx -> int_type, 1);
 
 	ctx -> longint_type = oberon_new_type_integer(8);
-	oberon_define_type(ctx -> world_scope, "LONGINT", ctx -> longint_type, 1);
+	oberon_define_type(ctx -> world_scope, "HUGEINT", ctx -> longint_type, 1);
 
 	ctx -> real_type = oberon_new_type_real(4);
 	oberon_define_type(ctx -> world_scope, "REAL", ctx -> real_type, 1);
@@ -3749,9 +3813,6 @@ register_default_types(oberon_context_t * ctx)
 	ctx -> longreal_type = oberon_new_type_real(8);
 	oberon_define_type(ctx -> world_scope, "LONGREAL", ctx -> longreal_type, 1);
 
-	ctx -> char_type = oberon_new_type_char(1);
-	oberon_define_type(ctx -> world_scope, "CHAR", ctx -> char_type, 1);
-
 	ctx -> set_type = oberon_new_type_set(4);
 	oberon_define_type(ctx -> world_scope, "SET", ctx -> set_type, 1);
 }
@@ -4001,6 +4062,15 @@ oberon_make_new_call(oberon_context_t * ctx, int num_args, oberon_expr_t * list_
 	oberon_assign(ctx, src, dst);
 }
 
+static void
+oberon_new_const(oberon_context_t * ctx, char * name, oberon_expr_t * expr)
+{
+	oberon_object_t * constant;
+	constant = oberon_define_object(ctx -> decl, name, OBERON_CLASS_CONST, true, false, false);
+	oberon_check_const(ctx, expr);
+	constant -> value = (oberon_item_t *) expr;
+}
+
 oberon_context_t *
 oberon_create_context(ModuleImportCallback import_module)
 {
@@ -4016,6 +4086,10 @@ oberon_create_context(ModuleImportCallback import_module)
 
 	register_default_types(ctx);
 
+	/* Constants */
+	oberon_new_const(ctx, "TRUE", oberon_make_boolean(ctx, true));
+	oberon_new_const(ctx, "FALSE", oberon_make_boolean(ctx, false));
+
 	/* Functions */
 	oberon_new_intrinsic(ctx, "ABS", oberon_make_abs_call, NULL);
 	oberon_new_intrinsic(ctx, "MIN", oberon_make_min_call, NULL);