Adding a negative lookahead.

src/text/prefix_primitives.c

@@ -39,6 +39,10 @@ char *prefix_epsilon(char *src) {
   return src;
 }
 
+char *prefix_not(char *src, prefix_matcher m) {
+  return m(src) ? NULL : src;
+}
+
 char *_prefix_alternatives(char *src, ...) {
   va_list ap;
   va_start(ap, src);

src/text/prefix_primitives.h

@@ -75,6 +75,7 @@ char *prefix_is_some_of(char *src, char *class);
 char *prefix_is_delimited_by(char *src, char *beg, char *end, int esc);
 
 char *prefix_epsilon(char *src);
+char *prefix_not(char *src, prefix_matcher m);
 char *_prefix_alternatives(char *src, ...);
 #define prefix_alternatives(src, ...) _prefix_alternatives(src, __VA_ARGS__, NULL)
 char *_prefix_sequence(char *src, ...);

src/text/test.c

@@ -3,6 +3,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include "prefix_primitives.h"
+#include "lexical_patterns.h"
 
 void print_slice(char *s, char *t) {
   if (t) {
@@ -74,6 +75,11 @@ int main() {
   test1(prefix_is_c_line_comment, lcomment);
   test1(prefix_is_c_line_comment, non_comment);
   
+  test1(prefix_epsilon, words);
+  
+  testn(prefix_not, words, prefix_is_puncts);
+  testn(prefix_not, words, prefix_is_alphas);
+  
   testn(prefix_sequence, id2, prefix_is_alphas, prefix_is_digits);
   testn(prefix_sequence, id2, prefix_is_alphas, prefix_is_puncts);
   
@@ -94,5 +100,8 @@ int main() {
   test1(prefix_is_integer, integer3);
   test1(prefix_is_integer, word2);
   
+  test1(prefix_is_word, word2);
+  test1(prefix_is_word, non_word);
+
   return 0;
 }