add ensure-not parser

extra/peg/peg-tests.factor

@@ -112,4 +112,28 @@ IN: temporary
 
 { f } [
   "bb" 0 <parse-state> "a" token ensure CHAR: a CHAR: z range 2array seq parse 
+] unit-test
+
+{ t } [
+  "a+b" 0 <parse-state>
+  "a" token "+" token dup ensure-not 2array seq "++" token 2array choice "b" token 3array seq
+  parse [ t ] [ f ] if
+] unit-test
+
+{ t } [
+  "a++b" 0 <parse-state>
+  "a" token "+" token dup ensure-not 2array seq "++" token 2array choice "b" token 3array seq
+  parse [ t ] [ f ] if
+] unit-test
+
+{ t } [
+  "a+b" 0 <parse-state>
+  "a" token "+" token "++" token 2array choice "b" token 3array seq
+  parse [ t ] [ f ] if
+] unit-test
+
+{ f } [
+  "a++b" 0 <parse-state>
+  "a" token "+" token "++" token 2array choice "b" token 3array seq
+  parse [ t ] [ f ] if
 ] unit-test

extra/peg/peg.factor

@@ -162,3 +162,15 @@ M: ensure-parser parse ( state parser -- result )
 
 : ensure ( parser -- parser )
   ensure-parser construct-boa init-parser ;
+
+TUPLE: ensure-not-parser p1 ;
+
+M: ensure-not-parser parse ( state parser -- result )
+   dupd ensure-not-parser-p1 parse [
+     drop f
+   ] [
+     ignore <parse-result>  
+   ] if ;
+
+: ensure-not ( parser -- parser )
+  ensure-not-parser construct-boa init-parser ;