gauche.cpat.diff

diff --git a/lib/gauche/regexp.scm b/lib/gauche/regexp.scm
index 76cdb44..3ca5c1c 100644
--- a/lib/gauche/regexp.scm
+++ b/lib/gauche/regexp.scm
@@ -190,7 +190,7 @@
         [(assert nassert)  (apply unparse-assert-like test)]
         [else (err "invalid AST in the test part of cpat" test)]))
     (seq yes)
-    (when no (disp "|") (seq no))
+    (unless (null? no) (disp "|") (seq no))
     (disp ")"))
 
   (define (unparse-assert-like op . asst)
diff --git a/src/regexp.c b/src/regexp.c
index e3d4670..7a621fd 100644
--- a/src/regexp.c
+++ b/src/regexp.c
@@ -922,7 +922,7 @@ static ScmObj rc1_parse(regcomp_ctx *ctx, int bolp, ScmObj groups)
                 npat = SCM_CDDR(elt);
             } else {
                 ypat = item;
-                npat = SCM_FALSE;
+                npat = SCM_NIL;
             }
             PUSH(SCM_LIST4(SCM_SYM_CPAT, cond, ypat, npat));
             bolp = FALSE;
@@ -1693,8 +1693,7 @@ static void rc3_rec(regcomp_ctx *ctx, ScmObj ast, int lastp)
             ocodep2 = ctx->codep;
             rc3_emit_offset(ctx, 0); /* will be patched */
             rc3_fill_offset(ctx, ocodep1, ctx->codep);
-            if (SCM_FALSEP(npat)) rc3_emit(ctx, RE_FAIL);
-            else rc3_seq(ctx, npat, lastp);
+            rc3_seq(ctx, npat, lastp);
             rc3_fill_offset(ctx, ocodep2, ctx->codep);
         } else {
             SCM_ASSERT(SCM_EQ(SCM_CAR(cond), SCM_SYM_ASSERT)
@@ -1712,8 +1711,7 @@ static void rc3_rec(regcomp_ctx *ctx, ScmObj ast, int lastp)
             ocodep3 = ctx->codep;
             rc3_emit_offset(ctx, 0); /* will be patched */
             rc3_fill_offset(ctx, ocodep2, ctx->codep);
-            if (SCM_FALSEP(npat)) rc3_emit(ctx, RE_FAIL);
-            else rc3_seq(ctx, npat, lastp);
+            rc3_seq(ctx, npat, lastp);
             rc3_fill_offset(ctx, ocodep3, ctx->codep);
         }
         return;
diff --git a/test/regexp.scm b/test/regexp.scm
index 1b2c1c3..7757df5 100644
--- a/test/regexp.scm
+++ b/test/regexp.scm
@@ -66,11 +66,11 @@
 (test-parse "(?<=ab)" '(0 #f (assert (lookbehind #\a #\b))))
 (test-parse "(?<!ab)" '(0 #f (nassert (lookbehind #\a #\b))))
 (test-parse "(?<name>a)" '(0 #f (1 name #\a)))
-(test-parse "(?(?=)y)" '(0 #f (cpat (assert) (#\y) #f)))
+(test-parse "(?(?=)y)" '(0 #f (cpat (assert) (#\y) ())))
 (test-parse "(?(?=)y|n)" '(0 #f (cpat (assert) (#\y) (#\n))))
-(test-parse "(?(?<=)y)" '(0 #f (cpat (assert (lookbehind)) (#\y) #f)))
+(test-parse "(?(?<=)y)" '(0 #f (cpat (assert (lookbehind)) (#\y) ())))
 (test-parse "(?(?<=)y|n)" '(0 #f (cpat (assert (lookbehind)) (#\y) (#\n))))
-(test-parse "()(?(1)y)" '(0 #f (1 #f) (cpat 1 (#\y) #f)))
+(test-parse "()(?(1)y)" '(0 #f (1 #f) (cpat 1 (#\y) ())))
 (test-parse "()(?(1)y|n)"'(0 #f (1 #f) (cpat 1 (#\y) (#\n))))
 (test-parse "()\\1" '(0 #f (1 #f) (backref . 1)))
 (test-parse "(?<name>)\\k<name>" '(0 #f (1 name) (backref . 1)))
@@ -653,11 +653,11 @@
 (test-re #/(a)(?(1)b)/ "ac" '())
 (test-re #/(a)?(?(1)b|c)/ "xb" '())
 (test-re #/(a)?(?(1)b|c)/ "xc" '("c" #f))
-(test-re #/(?(?<=a)b)/ "ab" '("b"))
-(test-re #/(?(?<=a)b)/ "ac" '())
-(test-re #/(?(?<=a)b)/ "xb" '())
-(test-re #/(?(?<=a)b)/ "ab" '("b"))
-(test-re #/(?(?<=a)b)/ "ac" '())
+(test-re #/(<)?[^<>]+(?(1)>)/ "<foo>" '("<foo>" "<"))
+(test-re #/(<)?[^<>]+(?(1)>)/ "foo" '("foo" #f))
+(test-re #/(?(?<=a)b)/ "ab" '(""))
+(test-re #/(?(?<=a)b)/ "ac" '(""))
+(test-re #/(?(?<=a)b)/ "xb" '(""))
 (test-parse "(?(?a)b|c)" (test-error))
 (test-re #/()(?(1))/ "" '("" ""))