diff --git a/examples/extern_C/README b/examples/extern_C/README
index fcdcb1e..4bc0873 100644
--- a/examples/extern_C/README
+++ b/examples/extern_C/README
@@ -4,3 +4,8 @@ This example show how to import an external function written in C in an Heptagon
 - Only functions with no side effects can be safely imported.
 - The imported function must have the same calling convention as generated code (inputs given by value, outputs in a f_out structure).
 - The generated code will include "mathext.h", that should define the step function
+
+To make it work:
+   heptc mathext.epi
+   heptc imports.ept
+   gcc -std=c99 -I . mathext.c imports_c/*.c -o imports
diff --git a/examples/extern_C/imports.ept b/examples/extern_C/imports.ept
index 19aab75..9037d61 100644
--- a/examples/extern_C/imports.ept
+++ b/examples/extern_C/imports.ept
@@ -3,4 +3,9 @@ open Mathext
 fun f(a:float) returns (o:float)
 let
   o = mycos(a);
+tel
+
+node g(a:float) returns (o:float)
+let
+  o = st_cos(a);
 tel
\ No newline at end of file
diff --git a/examples/extern_C/mathext.c b/examples/extern_C/mathext.c
index f3f7367..4e05bdf 100644
--- a/examples/extern_C/mathext.c
+++ b/examples/extern_C/mathext.c
@@ -1,7 +1,21 @@
 #include <math.h>
 #include "mathext.h"
 
-void mycos(float a, mycos_out *out)
+void mycos_step(float a, mycos_out *out)
 {
   out->o = cos(a);
 }
+
+void st_cos_reset(st_cos_mem *self)
+{
+  self->i = 0;
+  for(int j = 0; j < 100; ++j)
+    self->mem[j] = 0.0;
+}
+
+void st_cos_step(float a, st_cos_out *out, st_cos_mem *self)
+{
+  out->o = self->mem[self->i];
+  self->i = (self->i++) % 100;
+  self->mem[self->i] = cos(a);
+}
diff --git a/examples/extern_C/mathext.epi b/examples/extern_C/mathext.epi
index 3eb4f32..dd574d3 100644
--- a/examples/extern_C/mathext.epi
+++ b/examples/extern_C/mathext.epi
@@ -1 +1,3 @@
-val fun mycos(a:float) returns (o:float)
\ No newline at end of file
+val fun mycos(a:float) returns (o:float)
+
+val node st_cos(a:float) returns (o:float)
diff --git a/examples/extern_C/mathext.h b/examples/extern_C/mathext.h
index 9c01477..f20f922 100644
--- a/examples/extern_C/mathext.h
+++ b/examples/extern_C/mathext.h
@@ -1,8 +1,25 @@
-#ifdef MATHEXT_H
+#ifndef MATHEXT_H
 #define MATHEXT_H
 
-struct mycos_out {
+/* Example of a combinatorial function */
+typedef struct mycos_out {
   float o;
-};
+} mycos_out;
+
+void mycos_step(float a, mycos_out *o);
+
+/* Example of a statefull function. */
+typedef struct st_cos_out {
+  float o;
+} st_cos_out;
+
+typedef struct st_cos_mem {
+  int i;
+  float mem[100];
+} st_cos_mem;
+
+void st_cos_reset(st_cos_mem *self);
+void st_cos_step(float a, st_cos_out *out, st_cos_mem *self);
+
+#endif
 
-void mycos(float a, mycos_out *o);