diff --git a/README.md b/README.md
index f1faf11..cd15c62 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 ## Language Syntax
 
-A HCL program is composed of more expressions.
+A HCL program is composed of expressions.
 
 ## Keywords
 * nil
@@ -64,12 +64,16 @@ A HCL program is composed of more expressions.
 
 ## Defining a function
 
+```
 (defun function-name (arguments)
 	| local variables |
 	function body
 )
+```
 
+```
 (set function-name (lambda (arguments)
 	| local variables |
 	function body
 )
+```
diff --git a/lib/prim.c b/lib/prim.c
index e96bfde..6109734 100644
--- a/lib/prim.c
+++ b/lib/prim.c
@@ -400,6 +400,16 @@ static hcl_pfrc_t pf_is_dictionary (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 	HCL_STACK_SETRET (hcl, nargs, rv);
 	return HCL_PF_SUCCESS;
 }
+
+static hcl_pfrc_t pf_is_lambda (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
+{
+	hcl_oop_t rv, x;
+	x = HCL_STACK_GETARG(hcl, nargs, 0);
+	rv = (HCL_IS_CONTEXT(hcl, x))? hcl->_true: hcl->_false;
+	HCL_STACK_SETRET (hcl, nargs, rv);
+	return HCL_PF_SUCCESS;
+}
+
 /* ------------------------------------------------------------------------- */
 
 static hcl_pfrc_t pf_not (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
@@ -764,6 +774,7 @@ static pf_t builtin_prims[] =
 	{ 1, 1,                       pf_is_array,        6,  { 'a','r','r','a','y','?' } },
 	{ 1, 1,                       pf_is_bytearray,   10,  { 'b','y','t','e','a','r','r','a','y','?' } },
 	{ 1, 1,                       pf_is_dictionary,  11,  { 'd','i','c','t','i','o','n','a','r','y','?' } },
+	{ 1, 1,                       pf_is_lambda,       7,  { 'l','a','m','b','d','a','?' } },
 
 
 	{ 1, HCL_TYPE_MAX(hcl_oow_t), pf_number_add,      1,  { '+' } },