diff --git a/include/picrin/value.h b/include/picrin/value.h
index cfc958cf..f9f7bfda 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -82,6 +82,7 @@ pic_value pic_float_value(double);
 #define pic_true_p(v) ((v).type == PIC_VTYPE_TRUE)
 #define pic_false_p(v) ((v).type == PIC_VTYPE_FALSE)
 #define pic_undef_p(v) ((v).type == PIC_VTYPE_UNDEF)
+#define pic_float_p(v) ((v).type == PIC_VTYPE_FLOAT)
 #define pic_pair_p(v) (pic_type(v) == PIC_TT_PAIR)
 
 #endif
diff --git a/src/number.c b/src/number.c
index 084637d4..962a2c3f 100644
--- a/src/number.c
+++ b/src/number.c
@@ -2,6 +2,59 @@
 
 #include "picrin.h"
 
+static pic_value
+pic_number_real_p(pic_state *pic)
+{
+  pic_value v;
+
+  pic_get_args(pic, "o", &v);
+
+  return pic_bool_value(pic_float_p(v));
+}
+
+static pic_value
+pic_number_integer_p(pic_state *pic)
+{
+  pic_value v;
+
+  pic_get_args(pic, "o", &v);
+
+  if (pic_float_p(v)) {
+    double f = pic_float(v);
+
+    if (f == round(f)) {
+      return pic_true_value();
+    }
+  }
+  return pic_false_value();
+}
+
+static pic_value
+pic_number_infinite_p(pic_state *pic)
+{
+  pic_value v;
+
+  pic_get_args(pic, "o", &v);
+
+  if (pic_float_p(v) && isinf(pic_float(v)))
+    return pic_true_value();
+  else
+    return pic_false_value();
+}
+
+static pic_value
+pic_number_nan_p(pic_state *pic)
+{
+  pic_value v;
+
+  pic_get_args(pic, "o", &v);
+
+  if (pic_float_p(v) && isnan(pic_float(v)))
+    return pic_true_value();
+  else
+    return pic_false_value();
+}
+
 static pic_value
 pic_number_lt(pic_state *pic)
 {
@@ -17,13 +70,76 @@ pic_number_lt(pic_state *pic)
 }
 
 static pic_value
-pic_number_sqrt(pic_state *pic)
+pic_number_abs(pic_state *pic)
 {
   double f;
 
   pic_get_args(pic, "f", &f);
-  f = sqrt(f);
-  return pic_float_value(f);
+  return pic_float_value(fabs(f));
+}
+
+static pic_value
+pic_number_floor(pic_state *pic)
+{
+  double f;
+
+  pic_get_args(pic, "f", &f);
+
+  return pic_float_value(floor(f));
+}
+
+static pic_value
+pic_number_ceiling(pic_state *pic)
+{
+  double f;
+
+  pic_get_args(pic, "f", &f);
+
+  return pic_float_value(ceil(f));
+}
+
+static pic_value
+pic_number_truncate(pic_state *pic)
+{
+  double f;
+
+  pic_get_args(pic, "f", &f);
+
+  return pic_float_value(trunc(f));
+}
+
+static pic_value
+pic_number_round(pic_state *pic)
+{
+  double f;
+
+  pic_get_args(pic, "f", &f);
+
+  return pic_float_value(round(f));
+}
+
+static pic_value
+pic_number_exp(pic_state *pic)
+{
+  double f;
+
+  pic_get_args(pic, "f", &f);
+  return pic_float_value(exp(f));
+}
+
+static pic_value
+pic_number_log(pic_state *pic)
+{
+  double f,g;
+  int argc;
+
+  argc = pic_get_args(pic, "f|f", &f, &g);
+  if (argc == 1) {
+    return pic_float_value(log(f));
+  }
+  else {
+    return pic_float_value(log(f) / log(g));
+  }
 }
 
 static pic_value
@@ -78,23 +194,87 @@ pic_number_asin(pic_state *pic)
 
 static pic_value
 pic_number_atan(pic_state *pic)
+{
+  double f,g;
+  int argc;
+
+  argc = pic_get_args(pic, "f|g", &f, &g);
+  if (argc == 1) {
+    f = atan(f);
+    return pic_float_value(f);
+  }
+  else {
+    return pic_float_value(atan2(f,g));
+  }
+}
+
+static pic_value
+pic_number_square(pic_state *pic)
 {
   double f;
 
   pic_get_args(pic, "f", &f);
-  f = atan(f);
+
+  return pic_float_value(f * f);
+}
+
+static pic_value
+pic_number_sqrt(pic_state *pic)
+{
+  double f;
+
+  pic_get_args(pic, "f", &f);
+  f = sqrt(f);
   return pic_float_value(f);
 }
 
+static pic_value
+pic_number_expt(pic_state *pic)
+{
+  double f,g;
+
+  pic_get_args(pic, "ff", &f, &g);
+  return pic_float_value(pow(f,g));
+}
+
 void
 pic_init_number(pic_state *pic)
 {
+  int ai = pic_gc_arena_preserve(pic);
+
+  pic_defun(pic, "number?", pic_number_real_p);
+  pic_defun(pic, "complex?", pic_number_real_p);
+  pic_defun(pic, "real?", pic_number_real_p);
+  pic_defun(pic, "rational?", pic_number_integer_p);
+  pic_defun(pic, "integer?", pic_number_integer_p);
+  pic_gc_arena_restore(pic, ai);
+
+  pic_defun(pic, "infinite?", pic_number_infinite_p);
+  pic_defun(pic, "nan?", pic_number_nan_p);
+  pic_gc_arena_restore(pic, ai);
+
   pic_defun(pic, "<", pic_number_lt);
-  pic_defun(pic, "sqrt", pic_number_sqrt);
+
+  pic_defun(pic, "abs", pic_number_abs);
+
+  pic_defun(pic, "floor", pic_number_floor);
+  pic_defun(pic, "ceiling", pic_number_ceiling);
+  pic_defun(pic, "truncate", pic_number_truncate);
+  pic_defun(pic, "round", pic_number_round);
+  pic_gc_arena_restore(pic, ai);
+
+  pic_defun(pic, "exp", pic_number_exp);
+  pic_defun(pic, "log", pic_number_log);
   pic_defun(pic, "sin", pic_number_sin);
   pic_defun(pic, "cos", pic_number_cos);
   pic_defun(pic, "tan", pic_number_tan);
   pic_defun(pic, "acos", pic_number_acos);
   pic_defun(pic, "asin", pic_number_asin);
   pic_defun(pic, "atan", pic_number_atan);
+  pic_gc_arena_restore(pic, ai);
+
+  pic_defun(pic, "square", pic_number_square);
+  pic_defun(pic, "sqrt", pic_number_sqrt);
+  pic_defun(pic, "expt", pic_number_expt);
+  pic_gc_arena_restore(pic, ai);
 }