diff --git a/poly2d/Makefile b/poly2d/Makefile
index 11b0e59..83ce5f2 100644
--- a/poly2d/Makefile
+++ b/poly2d/Makefile
@@ -23,7 +23,7 @@ OBJS = v2d_intersect.o v2d_line_distance.o \
 CFLAGS_WARN = -Wall -Wshadow -Wmissing-prototypes \
 	      -Wmissing-declarations -Wno-format-zero-length
 
-CFLAGS = $(CFLAGS_WARN) -g
+CFLAGS = $(CFLAGS_WARN) -g -std=gnu99
 CXXFLAGS = -Wall -frounding-math
 LDFLAGS =
 LDLIBS = -lm
diff --git a/poly2d/poly2d.h b/poly2d/poly2d.h
index fec85ff..2b5cb9e 100644
--- a/poly2d/poly2d.h
+++ b/poly2d/poly2d.h
@@ -30,6 +30,34 @@ struct p2d {
 };
 
 
+/*
+ * forall_v2d* need -std=gnu99
+ */
+
+#define	forall_v2d_once(var, first)					\
+	for (const struct v2d *__fv2do_0 = (var = (first));		\
+	    var;							\
+	    var = var->next == __fv2do_0 ? NULL : var->next)
+
+#define	forall_v2d(var, first)						\
+	for (const struct v2d *__fv2d_0 = (var = (first));		\
+	    var;							\
+	    ({								\
+		var = __fv2d_0 ? var->next : NULL;			\
+		if (var == __fv2d_0)					\
+			__fv2d_0 = NULL;				\
+	    }))
+
+#define	forall_edges(a, b, first)					\
+	for (const struct v2d *__fe_0 =					\
+	   (a = (first), b = a ? a->next : a, a);			\
+	    a && b;							\
+	    ({								\
+		a = b;							\
+		b = b == __fe_0 ? NULL : b->next;			\
+	    }))
+
+
 /*
  * Polygon creation
  */
diff --git a/poly2d/test/Common b/poly2d/test/Common
index 2787aaa..deb88bf 100755
--- a/poly2d/test/Common
+++ b/poly2d/test/Common
@@ -14,6 +14,7 @@
 
 compile_and_run()
 {
+	CFLAGS="-Wall -Werror -g -std=gnu99 -I.."
 	LIBS="-lpoly2d -lCGAL -lCGAL_Core -lboost_thread"
 	LIBS="$LIBS -lstdc++ -lmpfr -lgmp -lm"
 
@@ -54,7 +55,7 @@ int main(void)
 	return 0;
 }
 EOF
-	gcc -Wall -Werror -g -I.. _.c -L.. $LIBS || return
+	gcc $CFLAGS _.c -L.. $LIBS || return
 	$VALGRIND ./a.out
 }
 
diff --git a/poly2d/test/forall b/poly2d/test/forall
new file mode 100755
index 0000000..fd88dec
--- /dev/null
+++ b/poly2d/test/forall
@@ -0,0 +1,121 @@
+#!/bin/sh
+. ./Common
+
+###############################################################################
+
+tst "forall_v2d_once, open polygon" <<EOF
+struct p2d *p = p2d_new();
+const struct v2d *v;
+
+p2d_append(p, v2d_new(0, 0));
+p2d_append(p, v2d_new(1, 0));
+p2d_append(p, v2d_new(2, 3));
+forall_v2d_once(v, p->v)
+	printf("%g %g\n", v->x, v->y);
+EOF
+
+expect <<EOF
+0 0
+1 0
+2 3
+EOF
+
+#------------------------------------------------------------------------------
+
+tst "forall_v2d_once, closed polygon" <<EOF
+struct p2d *p = p2d_new();
+const struct v2d *v;
+
+p2d_append(p, v2d_new(0, 0));
+p2d_append(p, v2d_new(1, 0));
+p2d_append(p, v2d_new(2, 3));
+p2d_close(p);
+forall_v2d_once(v, p->v)
+	printf("%g %g\n", v->x, v->y);
+EOF
+
+expect <<EOF
+0 0
+1 0
+2 3
+EOF
+
+#------------------------------------------------------------------------------
+
+tst "forall_v2d, open polygon" <<EOF
+struct p2d *p = p2d_new();
+const struct v2d *v;
+
+p2d_append(p, v2d_new(0, 0));
+p2d_append(p, v2d_new(1, 0));
+p2d_append(p, v2d_new(2, 3));
+forall_v2d(v, p->v)
+	printf("%g %g\n", v->x, v->y);
+EOF
+
+expect <<EOF
+0 0
+1 0
+2 3
+EOF
+
+#------------------------------------------------------------------------------
+
+tst "forall_v2d, closed polygon" <<EOF
+struct p2d *p = p2d_new();
+const struct v2d *v;
+
+p2d_append(p, v2d_new(0, 0));
+p2d_append(p, v2d_new(1, 0));
+p2d_append(p, v2d_new(2, 3));
+p2d_close(p);
+forall_v2d(v, p->v)
+	printf("%g %g\n", v->x, v->y);
+EOF
+
+expect <<EOF
+0 0
+1 0
+2 3
+0 0
+EOF
+
+#------------------------------------------------------------------------------
+
+tst "forall_edges, open polygon" <<EOF
+struct p2d *p = p2d_new();
+const struct v2d *a, *b;
+
+p2d_append(p, v2d_new(0, 0));
+p2d_append(p, v2d_new(1, 0));
+p2d_append(p, v2d_new(2, 3));
+forall_edges(a, b, p->v)
+	printf("%g %g %g %g\n", a->x, a->y, b->x, b->y);
+EOF
+
+expect <<EOF
+0 0 1 0
+1 0 2 3
+EOF
+
+#------------------------------------------------------------------------------
+
+tst "forall_edges, closed polygon" <<EOF
+struct p2d *p = p2d_new();
+const struct v2d *a, *b;
+
+p2d_append(p, v2d_new(0, 0));
+p2d_append(p, v2d_new(1, 0));
+p2d_append(p, v2d_new(2, 3));
+p2d_close(p);
+forall_edges(a, b, p->v)
+	printf("%g %g %g %g\n", a->x, a->y, b->x, b->y);
+EOF
+
+expect <<EOF
+0 0 1 0
+1 0 2 3
+2 3 0 0
+EOF
+
+###############################################################################