diff --git a/resources/grammar/c3.l b/resources/grammar/c3.l
index fea223517..4add6a072 100644
--- a/resources/grammar/c3.l
+++ b/resources/grammar/c3.l
@@ -54,6 +54,7 @@ int comment_level = 0;
 "$eval"         { count(); return(CT_EVAL); }
 "$evaltype"     { count(); return(CT_EVALTYPE); }
 "$extnameof"    { count(); return(CT_EXTNAMEOF); }
+"$feature"      { count(); return(CT_FEATURE); }
 "$for"          { count(); return(CT_FOR); }
 "$foreach"      { count(); return(CT_FOREACH); }
 "$if"           { count(); return(CT_IF); }
diff --git a/resources/grammar/grammar.y b/resources/grammar/grammar.y
index 7ac84bc2e..f085c9a36 100644
--- a/resources/grammar/grammar.y
+++ b/resources/grammar/grammar.y
@@ -30,7 +30,7 @@ void yyerror(char *s);
 %token CT_ENDFOR CT_ENDSWITCH BUILTIN IMPLIES INITIALIZE FINALIZE CT_ECHO CT_ASSERT CT_EVALTYPE CT_VATYPE
 %token TRY CATCH SCOPE DEFER LVEC RVEC OPTELSE CT_TYPEFROM CT_TYPEOF TLOCAL
 %token CT_VASPLAT INLINE DISTINCT CT_VACONST CT_NAMEOF CT_VAREF CT_VACOUNT CT_VAARG
-%token CT_SIZEOF CT_STRINGIFY CT_QNAMEOF CT_OFFSETOF CT_VAEXPR
+%token CT_SIZEOF CT_STRINGIFY CT_QNAMEOF CT_OFFSETOF CT_VAEXPR CT_FEATURE
 %token CT_EXTNAMEOF CT_EVAL CT_DEFINED CT_CHECKS CT_ALIGNOF ASSERT
 %token ASM CHAR_LITERAL REAL TRUE FALSE CT_CONST_IDENT
 %token LBRAPIPE RBRAPIPE HASH_CONST_IDENT
@@ -139,6 +139,7 @@ base_expr
 	| ct_arg '(' expr ')'
 	| ct_analyse '(' expr ')'
 	| CT_VACOUNT
+	| CT_FEATURE '(' CONST_IDENT ')'
 	| CT_CHECKS '(' expression_list ')'
 	| lambda_decl compound_statement
 	;
diff --git a/src/build/build_options.c b/src/build/build_options.c
index 6f91eb027..1e3c73b0c 100644
--- a/src/build/build_options.c
+++ b/src/build/build_options.c
@@ -108,6 +108,8 @@ static void usage(void)
 	OUTPUT("  -O3+                      - Aggressive optimization, single module.");
 	OUTPUT("  -Os+                      - Optimize for size, single module.");
 	OUTPUT("  -Oz+                      - Optimize for tiny size, single module.");
+	OUTPUT("  -D <name>                 - Add feature flag <name>.");
+	OUTPUT("  -U <name>                 - Remove feature flag <name>.");
 	OUTPUT("  --build-dir <dir>         - Override build output directory.");
 	OUTPUT("  --obj-out <dir>           - Override object file output directory.");
 	OUTPUT("  --llvm-out <dir>          - Override llvm output directory for '--emit-llvm'.");
@@ -203,9 +205,9 @@ static inline bool next_is_opt()
 	return args[arg_index + 1][0] == '-';
 }
 
-static inline bool match_longopt(const char* name)
+INLINE bool match_longopt(const char* name)
 {
-	return strcmp(&current_arg[2], name) == 0;
+	return str_eq(&current_arg[2], name);
 }
 
 static inline const char *match_argopt(const char* name)
@@ -385,6 +387,29 @@ static void add_linker_arg(BuildOptions *options, const char *arg)
 	options->linker_args[options->linker_arg_count++] = arg;
 }
 
+void update_feature_flags(const char ***flags, const char ***removed_flags, const char *arg, bool add)
+{
+	const char **to_remove_from = add ? *removed_flags : *flags;
+	unsigned len = vec_size(to_remove_from);
+	// Remove if it's in there.
+	for (unsigned i = 0; i < len; i++)
+	{
+		if (str_eq(to_remove_from[i], arg))
+		{
+			vec_erase_ptr_at(to_remove_from, i);
+			break;
+		}
+	}
+	const char ***to_add_to_ref = add ? flags : removed_flags;
+	unsigned add_len = vec_size(*to_add_to_ref);
+	for (unsigned i = 0; i < add_len; i++)
+	{
+		if (str_eq((*to_add_to_ref)[i], arg)) return;
+	}
+	vec_add(*to_add_to_ref, arg);
+}
+
+
 static int parse_multi_option(const char *start, unsigned count, const char** elements)
 {
 	const char *arg = current_arg;
@@ -435,18 +460,42 @@ static void parse_option(BuildOptions *options)
 		case 'h':
 			break;
 		case 'z':
-			if (at_end()) error_exit("error: -z needs a value");
-			add_linker_arg(options, next_arg());
-			return;
-		case 'o':
-			if (at_end()) error_exit("error: -o needs a name");
-			options->output_name = next_arg();
-			return;
-		case 'O':
-			if (options->optimization_setting_override != OPT_SETTING_NOT_SET)
+			if (match_shortopt("U"))
 			{
-				FAIL_WITH_ERR("Multiple optimization levels were set.");
+				if (at_end()) error_exit("error: -z needs a value.");
+				add_linker_arg(options, next_arg());
+				return;
 			}
+			break;
+		case 'o':
+			if (match_shortopt("o"))
+			{
+				if (at_end()) error_exit("error: -o needs a name.");
+				options->output_name = next_arg();
+				return;
+			}
+			break;
+		case 'D':
+			if (match_shortopt("D"))
+			{
+				if (at_end()) error_exit("error: -D needs a feature name.");
+				const char *arg = next_arg();
+				if (!str_is_valid_constant(arg)) error_exit("Invalid feature name '%s', expected an all-uppercase constant name.", arg);
+				update_feature_flags(&options->feature_names, &options->removed_feature_names, arg, true);
+				return;
+			}
+			break;
+		case 'U':
+			if (match_shortopt("U"))
+			{
+				if (at_end()) error_exit("error: -U needs a feature name.");
+				const char *arg = next_arg();
+				if (!str_is_valid_constant(arg)) error_exit("Invalid feature name '%s', expected an all-uppercase constant name.", arg);
+				update_feature_flags(&options->feature_names, &options->removed_feature_names, arg, false);
+				return;
+			}
+			break;
+		case 'O':
 			if (match_shortopt("O0+"))
 			{
 				options->optimization_setting_override = OPT_SETTING_O0_PLUS;
@@ -501,34 +550,54 @@ static void parse_option(BuildOptions *options)
 			}
 			return;
 		case 'E':
-			if (options->compile_option != COMPILE_NORMAL)
+			if (match_shortopt("E"))
 			{
-				FAIL_WITH_ERR("Illegal combination of compile options.");
+				if (options->compile_option != COMPILE_NORMAL)
+				{
+					FAIL_WITH_ERR("Illegal combination of compile options.");
+				}
+				options->compile_option = COMPILE_LEX_ONLY;
+				return;
 			}
-			options->compile_option = COMPILE_LEX_ONLY;
-			return;
+			break;
 		case 'L':
-			if (at_end() || next_is_opt()) error_exit("error: -L needs a directory.");
-			options->linker_lib_dir[options->linker_lib_dir_count++] = check_dir(next_arg());
-			return;
+			if (match_shortopt("L"))
+			{
+				if (at_end() || next_is_opt()) error_exit("error: -L needs a directory.");
+				options->linker_lib_dir[options->linker_lib_dir_count++] = check_dir(next_arg());
+				return;
+			}
+			break;
 		case 'l':
-			if (at_end() || next_is_opt()) error_exit("error: -l needs a library name.");
-			options->linker_libs[options->linker_lib_count++] = next_arg();
-			return;
+			if (match_shortopt("l"))
+			{
+				if (at_end() || next_is_opt()) error_exit("error: -l needs a library name.");
+				options->linker_libs[options->linker_lib_count++] = next_arg();
+				return;
+			}
+			break;
 		case 'P':
-			if (options->compile_option != COMPILE_NORMAL)
+			if (match_shortopt("P"))
 			{
-				FAIL_WITH_ERR("Illegal combination of compile options.");
+				if (options->compile_option != COMPILE_NORMAL)
+				{
+					FAIL_WITH_ERR("Illegal combination of compile options.");
+				}
+				options->compile_option = COMPILE_LEX_PARSE_ONLY;
+				return;
 			}
-			options->compile_option = COMPILE_LEX_PARSE_ONLY;
-			return;
+			break;
 		case 'C':
-			if (options->compile_option != COMPILE_NORMAL)
+			if (match_shortopt("C"))
 			{
-				FAIL_WITH_ERR("Illegal combination of compile options.");
+				if (options->compile_option != COMPILE_NORMAL)
+				{
+					FAIL_WITH_ERR("Illegal combination of compile options.");
+				}
+				options->compile_option = COMPILE_LEX_PARSE_CHECK_ONLY;
+				return;
 			}
-			options->compile_option = COMPILE_LEX_PARSE_CHECK_ONLY;
-			return;
+			break;
 		case '-':
 			if (match_longopt("tb"))
 			{
diff --git a/src/build/build_options.h b/src/build/build_options.h
index 0efc48a9a..94a0d412b 100644
--- a/src/build/build_options.h
+++ b/src/build/build_options.h
@@ -12,6 +12,7 @@
 #define MAX_INCLUDES 2048
 #define MAX_THREADS 0xFFFF
 
+void update_feature_flags(const char ***flags, const char ***removed_flag, const char *arg, bool add);
 
 typedef enum
 {
@@ -303,12 +304,14 @@ typedef struct BuildOptions_
 		const char *crtbegin;
 	} linuxpaths;
 	int build_threads;
-	const char** libraries_to_fetch;
-	const char** files;
-	const char* output_name;
-	const char* project_name;
-	const char* target_select;
-	const char* path;
+	const char **libraries_to_fetch;
+	const char **files;
+	const char **feature_names;
+	const char **removed_feature_names;
+	const char *output_name;
+	const char *project_name;
+	const char *target_select;
+	const char *path;
 	const char *template;
 	uint32_t symtab_size;
 	unsigned version;
@@ -441,6 +444,7 @@ typedef struct
 	const char *cflags;
 	const char **csource_dirs;
 	const char **csources;
+	const char **feature_list;
 	struct
 	{
 		SoftFloat soft_float : 3;
diff --git a/src/build/builder.c b/src/build/builder.c
index ee49f36eb..7c8fbd38c 100644
--- a/src/build/builder.c
+++ b/src/build/builder.c
@@ -192,6 +192,27 @@ static void update_build_target_from_options(BuildTarget *target, BuildOptions *
 
 	target->backend = options->backend;
 
+	// Remove feature flags
+	FOREACH_BEGIN(const char *remove_feature, options->removed_feature_names)
+		FOREACH_BEGIN_IDX(i, const char *feature, target->feature_list)
+			if (str_eq(feature, remove_feature))
+			{
+				vec_erase_ptr_at(target->feature_list, i);
+				break;
+			}
+		FOREACH_END();
+	FOREACH_END();
+
+	// Add feature flags
+	FOREACH_BEGIN(const char *add_feature, options->feature_names)
+		FOREACH_BEGIN_IDX(i, const char *feature, target->feature_list)
+			if (str_eq(feature, add_feature)) goto NEXT;
+		FOREACH_END();
+		vec_add(target->feature_list, add_feature);
+	NEXT:;
+	FOREACH_END();
+
+
 	update_build_target_with_opt_level(target, options->optimization_setting_override);
 
 	if (options->cc) target->cc = options->cc;
diff --git a/src/compiler/compiler.c b/src/compiler/compiler.c
index 4afb1b679..af693addb 100644
--- a/src/compiler/compiler.c
+++ b/src/compiler/compiler.c
@@ -45,6 +45,7 @@ void compiler_init(const char *std_lib_dir)
 	decltable_init(&global_context.symbols, INITIAL_SYMBOL_MAP);
 	decltable_init(&global_context.generic_symbols, INITIAL_GENERIC_SYMBOL_MAP);
 
+	htable_init(&global_context.features, 1024);
 	htable_init(&global_context.compiler_defines, 16 * 1024);
 	global_context.module_list = NULL;
 	global_context.generic_module_list = NULL;
@@ -820,6 +821,12 @@ void compile()
 	target_setup(&active_target);
 	resolve_libraries();
 
+	TokenType type = TOKEN_CONST_IDENT;
+	FOREACH_BEGIN(const char *feature_flag, active_target.feature_list)
+		feature_flag = symtab_preset(feature_flag, TOKEN_CONST_IDENT);
+		htable_set(&global_context.features, (void *)feature_flag, (void *)feature_flag);
+	FOREACH_END();
+
 	setup_int_define("C_SHORT_SIZE", platform_target.width_c_short, type_long);
 	setup_int_define("C_INT_SIZE", platform_target.width_c_int, type_long);
 	setup_int_define("C_LONG_SIZE", platform_target.width_c_long, type_long);
diff --git a/src/compiler/compiler_internal.h b/src/compiler/compiler_internal.h
index fe7cfce72..fa2d0d125 100644
--- a/src/compiler/compiler_internal.h
+++ b/src/compiler/compiler_internal.h
@@ -1703,6 +1703,7 @@ typedef struct
 	bool suppress_errors;
 	Decl ***locals_list;
 	HTable compiler_defines;
+	HTable features;
 	Module std_module;
 	DeclTable symbols;
 	DeclTable generic_symbols;
diff --git a/src/compiler/enums.h b/src/compiler/enums.h
index f48d3652c..746bce913 100644
--- a/src/compiler/enums.h
+++ b/src/compiler/enums.h
@@ -568,6 +568,7 @@ typedef enum
 	TOKEN_CT_EVALTYPE,          // $evaltype
 	TOKEN_CT_ERROR,             // $error
 	TOKEN_CT_EXTNAMEOF,         // $extnameof
+	TOKEN_CT_FEATURE,           // $feature
 	TOKEN_CT_FOR,               // $for
 	TOKEN_CT_FOREACH,           // $foreach
 	TOKEN_CT_IF,                // $if
diff --git a/src/compiler/parse_expr.c b/src/compiler/parse_expr.c
index 8a72b2997..7d3f10912 100644
--- a/src/compiler/parse_expr.c
+++ b/src/compiler/parse_expr.c
@@ -1017,6 +1017,7 @@ static Expr *parse_hash_ident(ParseContext *c, Expr *left)
 	return expr;
 }
 
+
 /**
  * ct_eval ::= CT_EVAL '(' expr ')'
  */
@@ -1104,7 +1105,7 @@ static Expr *parse_ct_embed(ParseContext *c, Expr *left)
 }
 
 /**
- * ct_call ::= (ALIGNOF | EXTNAMEOF | OFFSETOF | NAMEOF | QNAMEOF) '(' flat_path ')'
+ * ct_call ::= (CT_ALIGNOF | CT_FEATURE | CT_EXTNAMEOF | CT_OFFSETOF | CT_NAMEOF | CT_QNAMEOF) '(' flat_path ')'
  * flat_path ::= expr ('.' primary) | '[' expr ']')*
  */
 static Expr *parse_ct_call(ParseContext *c, Expr *left)
@@ -1909,6 +1910,7 @@ ParseRule rules[TOKEN_EOF + 1] = {
 		[TOKEN_CT_CHECKS] = { parse_ct_checks, NULL, PREC_NONE },
 		[TOKEN_CT_EMBED] = { parse_ct_embed, NULL, PREC_NONE },
 		[TOKEN_CT_EVAL] = { parse_ct_eval, NULL, PREC_NONE },
+		[TOKEN_CT_FEATURE] = { parse_ct_call, NULL, PREC_NONE },
 		[TOKEN_CT_EXTNAMEOF] = { parse_ct_call, NULL, PREC_NONE },
 		[TOKEN_CT_OFFSETOF] = { parse_ct_call, NULL, PREC_NONE },
 		[TOKEN_CT_NAMEOF] = { parse_ct_call, NULL, PREC_NONE },
diff --git a/src/compiler/parse_stmt.c b/src/compiler/parse_stmt.c
index 6343e99ce..28d3f0190 100644
--- a/src/compiler/parse_stmt.c
+++ b/src/compiler/parse_stmt.c
@@ -1208,50 +1208,51 @@ Ast *parse_stmt(ParseContext *c)
 			return parse_ct_foreach_stmt(c);
 		case TOKEN_CT_FOR:
 			return parse_ct_for_stmt(c);
-		case TOKEN_STAR:
 		case TOKEN_AMP:
-		case TOKEN_INTEGER:
-		case TOKEN_CHAR_LITERAL:
+		case TOKEN_AT:
+		case TOKEN_AT_CONST_IDENT:
+		case TOKEN_AT_IDENT:
+		case TOKEN_AT_TYPE_IDENT:
+		case TOKEN_BANG:
 		case TOKEN_BIT_NOT:
 		case TOKEN_BIT_OR:
 		case TOKEN_BIT_XOR:
+		case TOKEN_BUILTIN:
+		case TOKEN_BYTES:
+		case TOKEN_CHAR_LITERAL:
+		case TOKEN_CT_ALIGNOF:
+		case TOKEN_CT_CHECKS:
+		case TOKEN_CT_CONST_IDENT:
+		case TOKEN_CT_DEFINED:
+		case TOKEN_CT_EMBED:
+		case TOKEN_CT_EVAL:
+		case TOKEN_CT_EXTNAMEOF:
+		case TOKEN_CT_FEATURE:
+		case TOKEN_CT_IDENT:
+		case TOKEN_CT_NAMEOF:
+		case TOKEN_CT_OFFSETOF:
+		case TOKEN_CT_QNAMEOF:
+		case TOKEN_CT_SIZEOF:
+		case TOKEN_CT_STRINGIFY:
+		case TOKEN_CT_VAARG:
+		case TOKEN_CT_VACONST:
+		case TOKEN_CT_VACOUNT:
+		case TOKEN_CT_VAEXPR:
+		case TOKEN_CT_VAREF:
+		case TOKEN_FALSE:
+		case TOKEN_INTEGER:
+		case TOKEN_LBRAPIPE:
 		case TOKEN_LPAREN:
 		case TOKEN_MINUS:
-		case TOKEN_BANG:
+		case TOKEN_MINUSMINUS:
+		case TOKEN_NULL:
 		case TOKEN_OR:
 		case TOKEN_PLUS:
-		case TOKEN_MINUSMINUS:
 		case TOKEN_PLUSPLUS:
-		case TOKEN_CT_CONST_IDENT:
-		case TOKEN_CT_IDENT:
-		case TOKEN_STRING:
 		case TOKEN_REAL:
-		case TOKEN_FALSE:
-		case TOKEN_NULL:
+		case TOKEN_STAR:
+		case TOKEN_STRING:
 		case TOKEN_TRUE:
-		case TOKEN_LBRAPIPE:
-		case TOKEN_CT_OFFSETOF:
-		case TOKEN_CT_ALIGNOF:
-		case TOKEN_CT_EXTNAMEOF:
-		case TOKEN_CT_SIZEOF:
-		case TOKEN_CT_QNAMEOF:
-		case TOKEN_CT_NAMEOF:
-		case TOKEN_CT_DEFINED:
-		case TOKEN_CT_CHECKS:
-		case TOKEN_CT_STRINGIFY:
-		case TOKEN_CT_EVAL:
-		case TOKEN_BYTES:
-		case TOKEN_BUILTIN:
-		case TOKEN_CT_VACOUNT:
-		case TOKEN_CT_VAARG:
-		case TOKEN_CT_VAEXPR:
-		case TOKEN_CT_VACONST:
-		case TOKEN_CT_VAREF:
-		case TOKEN_AT_TYPE_IDENT:
-		case TOKEN_AT_CONST_IDENT:
-		case TOKEN_AT:
-		case TOKEN_AT_IDENT:
-		case TOKEN_CT_EMBED:
 			return parse_expr_stmt(c);
 		case TOKEN_ASSERT:
 			return parse_assert_stmt(c);
diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index bdf665e79..19e960dc1 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -7224,6 +7224,25 @@ FAIL_NO_INFER:
 	return false;
 }
 
+static inline bool sema_expr_analyse_ct_feature(SemaContext *context, Expr *expr)
+{
+	if (expr->resolve_status == RESOLVE_DONE) return expr_ok(expr);
+
+	Expr *inner = expr->ct_call_expr.main_var;
+	if (expr->ct_call_expr.flat_path) goto ERROR;
+	if (inner->expr_kind != EXPR_IDENTIFIER) goto ERROR;
+	if (inner->resolve_status != RESOLVE_NOT_DONE) goto ERROR;
+	if (!inner->identifier_expr.is_const) goto ERROR;
+
+	const char *name = inner->identifier_expr.ident;
+	void *value = htable_get(&global_context.features, (void *)name);
+	assert(!value || value == name);
+	expr_rewrite_const_bool(expr, type_bool, value != NULL);
+	return true;
+ERROR:
+	RETURN_SEMA_ERROR(inner, "Expected a feature name here, e.g. $feature(MY_FEATURE).");
+}
+
 static inline bool sema_expr_analyse_ct_defined(SemaContext *context, Expr *expr)
 {
 	if (expr->resolve_status == RESOLVE_DONE) return expr_ok(expr);
@@ -7491,6 +7510,8 @@ static inline bool sema_expr_analyse_ct_call(SemaContext *context, Expr *expr)
 		case TOKEN_CT_NAMEOF:
 		case TOKEN_CT_EXTNAMEOF:
 			return sema_expr_analyse_ct_nameof(context, expr);
+		case TOKEN_CT_FEATURE:
+			return sema_expr_analyse_ct_feature(context, expr);
 		default:
 			UNREACHABLE
 	}
diff --git a/src/compiler/tokens.c b/src/compiler/tokens.c
index d4e6cfc88..4cb3f37b9 100644
--- a/src/compiler/tokens.c
+++ b/src/compiler/tokens.c
@@ -342,6 +342,8 @@ const char *token_type_to_string(TokenType type)
 			return "$evaltype";
 		case TOKEN_CT_ERROR:
 			return "$error";
+		case TOKEN_CT_FEATURE:
+			return "$feature";
 		case TOKEN_CT_FOR:
 			return "$for";
 		case TOKEN_CT_FOREACH:
diff --git a/src/utils/lib.h b/src/utils/lib.h
index 2f7136784..dcc707c99 100644
--- a/src/utils/lib.h
+++ b/src/utils/lib.h
@@ -132,6 +132,11 @@ char *str_vprintf(const char *var, va_list list);
 void str_ellide_in_place(char *string, size_t max_size_shown);
 bool str_is_valid_lowercase_name(const char *string);
 bool str_is_valid_constant(const char *string);
+const char *str_unescape(char *string);
+bool str_is_identifier(const char *string);
+bool str_eq(const char *str1, const char *str2);
+bool str_is_type(const char *string);
+bool str_is_integer(const char *string);
 bool str_has_no_uppercase(const char *string);
 char *str_copy(const char *start, size_t str_len);
 
@@ -601,6 +606,19 @@ static inline bool char_is_lower_alphanum_(char c)
 	}
 }
 
+static inline bool char_is_upper_alphanum_(char c)
+{
+    switch (c)
+    {
+        case UPPER_CHAR_CASE:
+        case NUMBER_CHAR_CASE:
+        case '_':
+            return true;
+        default:
+            return false;
+    }
+}
+
 static inline bool char_is_letter(char c)
 {
 	switch (c)
diff --git a/src/utils/stringutils.c b/src/utils/stringutils.c
index 0fe14687a..95fb5004e 100644
--- a/src/utils/stringutils.c
+++ b/src/utils/stringutils.c
@@ -43,16 +43,91 @@ bool str_is_valid_lowercase_name(const char *string)
 	return true;
 }
 
+static const char *scan_past_underscore(const char *string)
+{
+    while (string[0] == '_') string++;
+    if (string[0] == '\0') return NULL;
+    return string;
+}
+
+const char *str_unescape(char *string)
+{
+    assert(string[0] == '"');
+    char c;
+    size_t index = 0;
+    while ((c = string++[0]) != '"')
+    {
+	    if (c == 0) return NULL;
+	    if (c == '\\')
+	    {
+		    c = string++[0];
+	    }
+	    string[index++] = c;
+    }
+	string[index] = '\0';
+	return string;
+}
+
+bool str_is_type(const char *string)
+{
+    string = scan_past_underscore(string);
+    if (!string) return false;
+    char c = string++[0];
+    if (!char_is_upper(c)) return false;
+    bool found_lower = false;
+    while ((c = *(string++)) != '\0')
+    {
+        if (char_is_lower(c))
+        {
+            found_lower = true;
+            continue;
+        }
+        if (!char_is_alphanum_(c)) return false;
+    }
+    return found_lower;
+}
+
+bool str_is_identifier(const char *string)
+{
+    string = scan_past_underscore(string);
+    if (!string) return false;
+    char c = string++[0];
+    if (!char_is_lower(c)) return false;
+    while ((c = *(string++)) != '\0')
+    {
+        if (!char_is_alphanum_(c)) return false;
+    }
+    return true;
+}
+
+bool str_eq(const char *str1, const char *str2)
+{
+	return str1 == str2 || strcmp(str1, str2) == 0;
+}
+
+bool str_is_integer(const char *string)
+{
+	if (string[0] == '-') string++;
+    if (!string[0]) return false;
+    char c;
+    // Must start with a lower case
+    while ((c = *(string++)) != '\0')
+    {
+        if (!char_is_digit(c)) return false;
+    }
+    return true;
+}
+
 bool str_is_valid_constant(const char *string)
 {
-	char c;
-	// Must start with a lower case
-	int length = 0;
-	while ((c = *(string++)) != '\0')
-	{
-		if (!char_is_upper(c) && c != '_') return false;
-	}
-	return true;
+    string = scan_past_underscore(string);
+    if (!string) return false;
+    char c = string++[0];
+    if (!char_is_upper(c)) return false;
+    while ((c = *(string++)) != '\0') {
+        if (!char_is_upper_alphanum_(c)) return false;
+    }
+    return true;
 }
 
 void str_ellide_in_place(char *string, size_t max_size_shown)
diff --git a/src/version.h b/src/version.h
index 35e0cac25..5b8748452 100644
--- a/src/version.h
+++ b/src/version.h
@@ -1 +1 @@
-#define COMPILER_VERSION "0.4.582"
\ No newline at end of file
+#define COMPILER_VERSION "0.4.583"
\ No newline at end of file