diff --git a/as/lexer.c b/as/lexer.c
index 33534d6..29a3847 100644
--- a/as/lexer.c
+++ b/as/lexer.c
@@ -20,31 +20,9 @@
 #include <stdio.h>
 #include <string.h>
 #include "asm_error.h"
+#include "lexer/grammar.h"
 #include "lexer.h"
 
-/**
- * macros for the grammar.
- */
-
-// Numbers is defined as [0-9]
-#define number(x) ((x) >= '0' && (x) <= '9')
-
-// The first digit can however also contain '-'
-#define first_number(x) (number(x) || (x) == '-' )
-
-// First character in strings can be [a-z][A-Z] or '_'
-#define first_string(x)			\
-	(  ((x) >= 'a' && (x) <= 'z')   \
-	|| ((x) >= 'A' && (x) <= 'Z')	\
-	||  (x) == '_'			)
-
-// All characters after can also include numbers or ':'
-#define string(x) \
-	(first_string(x) || number(x))
-
-#define space(x) ((x) == ' ' || (x) == '\t' || (x) == '\r')
-
-
 struct opcode_ent {
 	char *  name;
 	uint8_t code;
@@ -82,7 +60,7 @@ static int read_next(struct lexer *lex) {
 
  		if (c == ';') {
  			comment = 1;
- 		} else if (!space(c)) {
+ 		} else if (!lexer_is_space(c)) {
  			break;
  		}
  	}
@@ -95,7 +73,7 @@ static int read_hex(FILE *fp, int *out) {
 
 	while((c = fgetc(fp)) != EOF) {
 		char n = 0;
-		if (number(c)) {
+		if (lexer_is_num(c)) {
 			n = c - '0';
 		}
 		else if (  (c >= 'a' && c <= 'f')
@@ -124,7 +102,7 @@ static int read_dec(FILE *fp, int neg, int *out) {
 	int c, val = 0;
 
 	while((c = fgetc(fp)) != EOF) {
-		if (!number(c)) {
+		if (!lexer_is_num(c)) {
 			ungetc(c, fp);
 			break;
 		}
@@ -188,7 +166,7 @@ static int read_string(FILE *fp, char *buf, size_t len) {
 
 	while((c = fgetc(fp)) != EOF && i < len) {
 
-		if (string(c)) {
+		if (lexer_is_string(c)) {
 			buf[i++] = c;
 		} else {
 			if (c == ':') {
@@ -245,12 +223,12 @@ int lexer_get_next(struct lexer *lex) {
 			return -1;
 		break;
 	default:
-		if (first_number(ch)) {
+		if (lexer_is_num_start(ch)) {
 			ungetc(ch, lex->fp);
 			lex->token.type = TOKEN_NUMBER;
 			if (parse_number(lex) < 0)
 				return -1;
-		} else if (first_string(ch)) {
+		} else if (lexer_is_string_start(ch)) {
 			char buf[32];
 			ungetc(ch, lex->fp);
 			lex->token.type = read_string(lex->fp, buf, sizeof(buf));
diff --git a/as/lexer/grammar.h b/as/lexer/grammar.h
new file mode 100644
index 0000000..68ef410
--- /dev/null
+++ b/as/lexer/grammar.h
@@ -0,0 +1,43 @@
+/* lexer/grammar.h
+ *
+ * Macros for the grammar.
+ *
+ *   Copyright (C) 2018-2019   Henrik Hautakoski <henrik.hautakoski@gmail.com>
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ *   MA 02110-1301, USA.
+ */
+#ifndef ASM_LEXER_GRAMMAR_H
+#define ASM_LEXER_GRAMMAR_H
+
+// Numbers is defined as [0-9]
+#define lexer_is_num(x) ((x) >= '0' && (x) <= '9')
+
+// The first digit can however also contain '-'
+#define lexer_is_num_start(x) (lexer_is_num(x) || (x) == '-' )
+
+// First character in strings can be [a-z][A-Z] or '_'
+#define lexer_is_string_start(x)			\
+	(  ((x) >= 'a' && (x) <= 'z')   \
+	|| ((x) >= 'A' && (x) <= 'Z')	\
+	||  (x) == '_'			)
+
+// All characters after can also include numbers or ':'
+#define lexer_is_string(x) \
+	(lexer_is_string_start(x) || lexer_is_num(x))
+
+#define lexer_is_space(x) ((x) == ' ' || (x) == '\t' || (x) == '\r')
+
+#endif /* ASM_LEXER_GRAMMAR_H */