diff --git a/lib/Makefile.am b/lib/Makefile.am
index 5d0e7f7..66a6da4 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -56,6 +56,7 @@ libhcl_la_SOURCES = \
 	hcl.c \
 	heap.c \
 	logfmt.c \
+	number.c \
 	obj.c \
 	opt-imp.h \
 	opt.c \
diff --git a/lib/Makefile.in b/lib/Makefile.in
index ddd8e03..39e9f5b 100644
--- a/lib/Makefile.in
+++ b/lib/Makefile.in
@@ -160,10 +160,10 @@ am_libhcl_la_OBJECTS = libhcl_la-bigint.lo libhcl_la-comp.lo \
 	libhcl_la-debug.lo libhcl_la-decode.lo libhcl_la-dic.lo \
 	libhcl_la-err.lo libhcl_la-exec.lo libhcl_la-gc.lo \
 	libhcl_la-hcl.lo libhcl_la-heap.lo libhcl_la-logfmt.lo \
-	libhcl_la-obj.lo libhcl_la-opt.lo libhcl_la-prim.lo \
-	libhcl_la-print.lo libhcl_la-rbt.lo libhcl_la-read.lo \
-	libhcl_la-sym.lo libhcl_la-tmr.lo libhcl_la-utf8.lo \
-	libhcl_la-utl.lo
+	libhcl_la-number.lo libhcl_la-obj.lo libhcl_la-opt.lo \
+	libhcl_la-prim.lo libhcl_la-print.lo libhcl_la-rbt.lo \
+	libhcl_la-read.lo libhcl_la-sym.lo libhcl_la-tmr.lo \
+	libhcl_la-utf8.lo libhcl_la-utl.lo
 libhcl_la_OBJECTS = $(am_libhcl_la_OBJECTS)
 AM_V_lt = $(am__v_lt_@AM_V@)
 am__v_lt_ = $(am__v_lt_@AM_DEFAULT_V@)
@@ -420,6 +420,7 @@ pdfdir = @pdfdir@
 prefix = @prefix@
 program_transform_name = @program_transform_name@
 psdir = @psdir@
+runstatedir = @runstatedir@
 sbindir = @sbindir@
 sharedstatedir = @sharedstatedir@
 srcdir = @srcdir@
@@ -468,6 +469,7 @@ libhcl_la_SOURCES = \
 	hcl.c \
 	heap.c \
 	logfmt.c \
+	number.c \
 	obj.c \
 	opt-imp.h \
 	opt.c \
@@ -684,6 +686,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-hcl.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-heap.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-logfmt.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-number.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-obj.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-opt.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/libhcl_la-prim.Plo@am__quote@
@@ -798,6 +801,13 @@ libhcl_la-logfmt.lo: logfmt.c
 @AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
 @am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libhcl_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o libhcl_la-logfmt.lo `test -f 'logfmt.c' || echo '$(srcdir)/'`logfmt.c
 
+libhcl_la-number.lo: number.c
+@am__fastdepCC_TRUE@	$(AM_V_CC)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libhcl_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT libhcl_la-number.lo -MD -MP -MF $(DEPDIR)/libhcl_la-number.Tpo -c -o libhcl_la-number.lo `test -f 'number.c' || echo '$(srcdir)/'`number.c
+@am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/libhcl_la-number.Tpo $(DEPDIR)/libhcl_la-number.Plo
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	$(AM_V_CC)source='number.c' object='libhcl_la-number.lo' libtool=yes @AMDEPBACKSLASH@
+@AMDEP_TRUE@@am__fastdepCC_FALSE@	DEPDIR=$(DEPDIR) $(CCDEPMODE) $(depcomp) @AMDEPBACKSLASH@
+@am__fastdepCC_FALSE@	$(AM_V_CC@am__nodep@)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libhcl_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -c -o libhcl_la-number.lo `test -f 'number.c' || echo '$(srcdir)/'`number.c
+
 libhcl_la-obj.lo: obj.c
 @am__fastdepCC_TRUE@	$(AM_V_CC)$(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(libhcl_la_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -MT libhcl_la-obj.lo -MD -MP -MF $(DEPDIR)/libhcl_la-obj.Tpo -c -o libhcl_la-obj.lo `test -f 'obj.c' || echo '$(srcdir)/'`obj.c
 @am__fastdepCC_TRUE@	$(AM_V_at)$(am__mv) $(DEPDIR)/libhcl_la-obj.Tpo $(DEPDIR)/libhcl_la-obj.Plo
diff --git a/lib/hcl-prv.h b/lib/hcl-prv.h
index 94cfb20..e10001f 100644
--- a/lib/hcl-prv.h
+++ b/lib/hcl-prv.h
@@ -831,7 +831,7 @@ int hcl_utf8toucs (
 );
 
 /* ========================================================================= */
-/* bigint.c   TODO: remove bigint                                            */
+/* bigint.c                                                                  */
 /* ========================================================================= */
 int hcl_isint (
 	hcl_t*    hcl,
@@ -963,6 +963,20 @@ hcl_oop_t hcl_inttostr (
 	int         ngc
 );
 
+/* ========================================================================= */
+/* number.c                                                                    */
+/* ========================================================================= */
+hcl_oop_t hcl_addnums (
+	hcl_t*       hcl,
+	hcl_oop_t    x,
+	hcl_oop_t    y
+);
+
+hcl_oop_t hcl_subnums (
+	hcl_t*       hcl,
+	hcl_oop_t    x,
+	hcl_oop_t    y
+);
 /* ========================================================================= */
 /* comp.c                                                                    */
 /* ========================================================================= */
diff --git a/lib/hcl.h b/lib/hcl.h
index abca4d4..b33b118 100644
--- a/lib/hcl.h
+++ b/lib/hcl.h
@@ -1435,6 +1435,7 @@ typedef enum hcl_concode_t hcl_concode_t;
 #define HCL_IS_NBIGINT(hcl,v) (HCL_OOP_IS_POINTER(v) && HCL_OBJ_GET_FLAGS_BRAND(v) == HCL_BRAND_NBIGINT)
 #define HCL_IS_BIGINT(hcl,v) (HCL_OOP_IS_POINTER(v) && (HCL_OBJ_GET_FLAGS_BRAND(v) == HCL_BRAND_PBIGINT || HCL_OBJ_GET_FLAGS_BRAND(v) == HCL_BRAND_NBIGINT))
 #define HCL_IS_STRING(hcl,v) (HCL_OOP_IS_POINTER(v) && HCL_OBJ_GET_FLAGS_BRAND(v) == HCL_BRAND_STRING)
+#define HCL_IS_FPDEC(hcl,v) (HCL_OOP_IS_POINTER(v) && HCL_OBJ_GET_FLAGS_BRAND(v) == HCL_BRAND_FPDEC)
 
 #define HCL_CONS_CAR(v)  (((hcl_cons_t*)(v))->car)
 #define HCL_CONS_CDR(v)  (((hcl_cons_t*)(v))->cdr)
@@ -1905,6 +1906,12 @@ HCL_EXPORT hcl_oop_t hcl_makestring (
 	int               ngc
 );
 
+HCL_EXPORT hcl_oop_t hcl_makefpdec (
+	hcl_t*            hcl,
+	hcl_oop_t         value,
+	hcl_ooi_t         scale
+);
+
 HCL_EXPORT hcl_oop_t hcl_makedic (
 	hcl_t*            hcl, 
 	hcl_oow_t         inisize /* initial bucket size */
diff --git a/lib/number.c b/lib/number.c
new file mode 100644
index 0000000..5c6515a
--- /dev/null
+++ b/lib/number.c
@@ -0,0 +1,126 @@
+/*
+ * $Id$
+ *
+    Copyright (c) 2016-2018 Chung, Hyung-Hwan. All rights reserved.
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+    1. Redistributions of source code must retain the above copyright
+       notice, this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright
+       notice, this list of conditions and the following disclaimer in the
+       documentation and/or other materials provided with the distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
+    IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+    NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+    THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "hcl-prv.h"
+
+static hcl_ooi_t equalize_scale (hcl_t* hcl, hcl_oop_fpdec_t x, hcl_oop_fpdec_t y)
+{
+	hcl_ooi_t xs, ys;
+	
+	xs = HCL_OOP_TO_SMOOI(x->scale);
+	ys = HCL_OOP_TO_SMOOI(y->scale);
+
+	if (xs < ys)
+	{
+	/* TODO: don't change x or y. create new objects */
+		x->scale = y->scale;
+		hcl_pushtmp(hcl, &x);
+		while (xs < ys)
+		{
+			x->value = hcl_mulints(hcl, x->value, HCL_SMOOI_TO_OOP(10));
+			xs++;
+		}
+		hcl_poptmp(hcl);
+	}
+	else if (xs > ys)
+	{
+		y->scale = x->scale;
+		hcl_pushtmp(hcl, &y);
+		while (ys < xs)
+		{
+			y->value = hcl_mulints(hcl, y->value, HCL_SMOOI_TO_OOP(10));
+			ys++;
+		}
+		hcl_poptmp(hcl);
+	}
+
+	return xs;
+}
+
+hcl_oop_t hcl_addnums (hcl_t* hcl, hcl_oop_t x, hcl_oop_t y)
+{
+	if (HCL_IS_FPDEC(hcl, x))
+	{
+		if (HCL_IS_FPDEC(hcl, y))
+		{
+			hcl_oop_t v;
+			hcl_ooi_t scale;
+
+/* TODO: error handling */
+			hcl_pushtmp (hcl, &x);
+			hcl_pushtmp (hcl, &y);
+			scale = equalize_scale (hcl, x, y);
+			v = hcl_addints(hcl, ((hcl_oop_fpdec_t)x)->value, ((hcl_oop_fpdec_t)y)->value);
+			hcl_poptmps (hcl, 2);
+			return hcl_makefpdec(hcl, v, scale);
+		}
+		else
+		{
+		}
+	}
+	else
+	{
+		if (HCL_IS_FPDEC(hcl, y))
+		{
+		}
+		else
+		{
+			return hcl_addints(hcl, x, y);
+		}
+	}
+}
+
+hcl_oop_t hcl_subnums (hcl_t* hcl, hcl_oop_t x, hcl_oop_t y)
+{
+	if (HCL_IS_FPDEC(hcl, x))
+	{
+		if (HCL_IS_FPDEC(hcl, y))
+		{
+			hcl_oop_t v;
+			hcl_ooi_t scale;
+
+			hcl_pushtmp (hcl, &x);
+			hcl_pushtmp (hcl, &y);
+			scale = equalize_scale (hcl, x, y);
+			v = hcl_subints(hcl, ((hcl_oop_fpdec_t)x)->value, ((hcl_oop_fpdec_t)y)->value);
+			hcl_poptmps (hcl, 2);
+			return hcl_makefpdec(hcl, v, scale);
+		}
+		else
+		{
+		}
+	}
+	else
+	{
+		if (HCL_IS_FPDEC(hcl, y))
+		{
+		}
+		else
+		{
+			return hcl_subints(hcl, x, y);
+		}
+	}
+}
diff --git a/lib/obj.c b/lib/obj.c
index 7b10758..b232174 100644
--- a/lib/obj.c
+++ b/lib/obj.c
@@ -269,6 +269,28 @@ hcl_oop_t hcl_makestring (hcl_t* hcl, const hcl_ooch_t* ptr, hcl_oow_t len, int
 }
 
 
+hcl_oop_t hcl_makefpdec (hcl_t* hcl, hcl_oop_t value, hcl_ooi_t scale)
+{
+	hcl_oop_fpdec_t f;
+
+	if (!HCL_IN_SMOOI_RANGE(scale))
+	{
+		hcl_seterrbfmt (hcl, HCL_EINVAL, "fpdec scale too large - %zd", scale);
+		return HCL_NULL;
+	}
+	
+	hcl_pushtmp (hcl, &value);
+	f = (hcl_oop_fpdec_t)hcl_allocoopobj (hcl, HCL_BRAND_FPDEC, HCL_FPDEC_NAMED_INSTVARS);
+	hcl_poptmp (hcl);
+
+	if (!f) return HCL_NULL;
+
+	f->value = value;
+	f->scale = HCL_SMOOI_TO_OOP(scale);
+
+	return (hcl_oop_t)f;
+}
+
 /* ------------------------------------------------------------------------ *
  * NGC HANDLING
  * ------------------------------------------------------------------------ */
diff --git a/lib/prim.c b/lib/prim.c
index ffbb76e..a077ada 100644
--- a/lib/prim.c
+++ b/lib/prim.c
@@ -385,7 +385,8 @@ static hcl_pfrc_t pf_integer_add (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 	for (i = 1; i < nargs; i++)
 	{
 		arg = HCL_STACK_GETARG(hcl, nargs, i);
-		ret = hcl_addints(hcl, ret, arg);
+		/*ret = hcl_addints(hcl, ret, arg);*/
+		ret = hcl_addnums(hcl, ret, arg);
 		if (!ret) return HCL_PF_FAILURE;
 	}
 
@@ -402,7 +403,8 @@ static hcl_pfrc_t pf_integer_sub (hcl_t* hcl, hcl_mod_t* mod, hcl_ooi_t nargs)
 	for (i = 1; i < nargs; i++)
 	{
 		arg = HCL_STACK_GETARG(hcl, nargs, i);
-		ret = hcl_subints(hcl, ret, arg);
+		/*ret = hcl_subints(hcl, ret, arg);*/
+		ret = hcl_subnums(hcl, ret, arg);
 		if (!ret) return HCL_PF_FAILURE;
 	}
 
diff --git a/lib/read.c b/lib/read.c
index 8e86a02..ba6ee44 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -246,7 +246,6 @@ static hcl_oop_t string_to_fpdec (hcl_t* hcl, hcl_oocs_t* str, const hcl_ioloc_t
 	hcl_oow_t pos;
 	hcl_oow_t scale = 0;
 	hcl_oop_t v;
-	hcl_oop_fpdec_t f;
 
 	pos = str->len;
 	while (pos > 0)
@@ -269,17 +268,7 @@ static hcl_oop_t string_to_fpdec (hcl_t* hcl, hcl_oocs_t* str, const hcl_ioloc_t
 	if (scale > 0) HCL_MEMMOVE (&str->ptr[pos + 1], &str->ptr[pos], scale * HCL_SIZEOF(str->ptr[0]));
 	if (!v) return HCL_NULL;
 
-	hcl_pushtmp (hcl, &v);
-	f = (hcl_oop_fpdec_t)hcl_makearray (hcl, HCL_FPDEC_NAMED_INSTVARS, 0);
-	hcl_poptmp (hcl);
-
-	if (!f) return HCL_NULL;
-
-	HCL_OBJ_SET_FLAGS_BRAND(f, HCL_BRAND_FPDEC);
-	f->value = v;
-	f->scale = HCL_SMOOI_TO_OOP(scale);
-
-	return f;
+	return hcl_makefpdec (hcl, v, scale);
 }
 
 static HCL_INLINE int is_spacechar (hcl_ooci_t c)