diff --git a/lib/ext/file.c b/lib/ext/file.c
index 4dc55229..69826ccd 100644
--- a/lib/ext/file.c
+++ b/lib/ext/file.c
@@ -123,6 +123,34 @@ pic_file_open_output_file(pic_state *pic)
   return pic_fopen(pic, fp, "w");
 }
 
+pic_value
+pic_file_open_binary_input_file(pic_state *pic)
+{
+  const char *fname;
+  FILE *fp;
+
+  pic_get_args(pic, "z", &fname);
+
+  if ((fp = fopen(fname, "rb")) == NULL) {
+    file_error(pic, "could not open file", 1, pic_cstr_value(pic, fname));
+  }
+  return pic_fopen(pic, fp, "rb");
+}
+
+pic_value
+pic_file_open_binary_output_file(pic_state *pic)
+{
+  const char *fname;
+  FILE *fp;
+
+  pic_get_args(pic, "z", &fname);
+
+  if ((fp = fopen(fname, "wb")) == NULL) {
+    file_error(pic, "could not open file", 1, pic_cstr_value(pic, fname));
+  }
+  return pic_fopen(pic, fp, "wb");
+}
+
 pic_value
 pic_file_exists_p(pic_state *pic)
 {
@@ -154,13 +182,21 @@ pic_file_delete(pic_state *pic)
 void
 pic_init_file(pic_state *pic)
 {
-  pic_defvar(pic, "current-input-port", pic_fopen(pic, stdin, "r"));
-  pic_defvar(pic, "current-output-port", pic_fopen(pic, stdout, "w"));
-  pic_defvar(pic, "current-error-port", pic_fopen(pic, stdout, "w"));
+  pic_value i, o, e;
+
+  i = pic_fopen(pic, stdin, "r");
+  o = pic_fopen(pic, stdout, "w");
+  e = pic_fopen(pic, stderr, "w");
+  pic_setvbuf(pic, i, NULL, PIC_IOLBF, 0);
+  pic_setvbuf(pic, o, NULL, PIC_IOLBF, 0);
+  pic_defvar(pic, "current-input-port", i);
+  pic_defvar(pic, "current-output-port", o);
+  pic_defvar(pic, "current-error-port", e);
+
   pic_defun(pic, "open-input-file", pic_file_open_input_file);
   pic_defun(pic, "open-output-file", pic_file_open_output_file);
-  pic_defun(pic, "open-binary-input-file", pic_file_open_input_file);
-  pic_defun(pic, "open-binary-output-file", pic_file_open_output_file);
+  pic_defun(pic, "open-binary-input-file", pic_file_open_binary_input_file);
+  pic_defun(pic, "open-binary-output-file", pic_file_open_binary_output_file);
   pic_defun(pic, "file-exists?", pic_file_exists_p);
   pic_defun(pic, "delete-file", pic_file_delete);
 }
diff --git a/lib/ext/main.c b/lib/ext/main.c
index acb17dda..dc2d2952 100644
--- a/lib/ext/main.c
+++ b/lib/ext/main.c
@@ -17,10 +17,12 @@ main(int argc, char *argv[])
     if (argc == 1) {            /* repl */
       while (1) {
         pic_printf(pic, "> ");
+        pic_fflush(pic, pic_stdout(pic));
         e = pic_funcall(pic, "read", 0);
         if (pic_eof_p(pic, e))
           break;
-        pic_printf(pic, "~s\n", pic_funcall(pic, "eval", 1, e));
+        pic_funcall(pic, "write", 1, pic_funcall(pic, "eval", 1, e));
+        pic_printf(pic, "\n");
       }
     } else if (argc == 2) {     /* load file */
       FILE *file = fopen(argv[1], "r");
diff --git a/lib/include/picrin.h b/lib/include/picrin.h
index 4e6f71a2..2d075897 100644
--- a/lib/include/picrin.h
+++ b/lib/include/picrin.h
@@ -258,6 +258,10 @@ typedef struct {
 #define PIC_SEEK_END 1
 #define PIC_SEEK_SET 2
 
+#define PIC_IONBF 0
+#define PIC_IOLBF 1
+#define PIC_IOFBF 2
+
 #define pic_stdin(pic) pic_funcall(pic, "current-input-port", 0)
 #define pic_stdout(pic) pic_funcall(pic, "current-output-port", 0)
 #define pic_stderr(pic) pic_funcall(pic, "current-error-port", 0)
@@ -281,13 +285,11 @@ int pic_fputs(pic_state *, const char *s, pic_value port);
 char *pic_fgets(pic_state *, char *s, int size, pic_value port);
 int pic_ungetc(pic_state *, int c, pic_value port);
 int pic_fflush(pic_state *, pic_value port);
+int pic_setvbuf(pic_state *, pic_value port, char *buf, int mode, size_t size);
 /* formatted output */
 int pic_printf(pic_state *, const char *fmt, ...);
 int pic_fprintf(pic_state *, pic_value port, const char *fmt, ...);
 int pic_vfprintf(pic_state *, pic_value port, const char *fmt, va_list ap);
-/* string buffer */
-pic_value pic_fmemopen(pic_state *, const char *buf, int len, const char *mode); /* deprecated */
-int pic_fgetbuf(pic_state *, pic_value port, const char **buf, int *len); /* deprecated */
 
 
 /*
diff --git a/lib/object.h b/lib/object.h
index 9507e376..bbe14d73 100644
--- a/lib/object.h
+++ b/lib/object.h
@@ -129,12 +129,13 @@ struct proc {
 };
 
 enum {
-  FILE_READ  = 01,
-  FILE_WRITE = 02,
-  FILE_UNBUF = 04,
-  FILE_EOF   = 010,
-  FILE_ERR   = 020,
-  FILE_LNBUF = 040
+  FILE_READ   = 01,
+  FILE_WRITE  = 02,
+  FILE_UNBUF  = 04,
+  FILE_EOF    = 010,
+  FILE_ERR    = 020,
+  FILE_LNBUF  = 040,
+  FILE_SETBUF = 0100
 };
 
 struct port {
diff --git a/lib/port.c b/lib/port.c
index e4dca466..21feada1 100644
--- a/lib/port.c
+++ b/lib/port.c
@@ -35,13 +35,13 @@ pic_fclose(pic_state *pic, pic_value port)
     return 0;
   pic_fflush(pic, port);
   fp->flag = 0;
-  if (fp->base != fp->buf)
+  if (fp->base != fp->buf && (fp->flag & FILE_SETBUF) == 0)
     pic_free(pic, fp->base);
   return fp->vtable->close(pic, fp->cookie);
 }
 
 void
-pic_clearerr(pic_state *PIC_UNUSED(pic), pic_value port)
+pic_clearerr(pic_state *pic, pic_value port)
 {
   struct file *fp = &port_ptr(pic, port)->file;
 
@@ -49,7 +49,7 @@ pic_clearerr(pic_state *PIC_UNUSED(pic), pic_value port)
 }
 
 int
-pic_feof(pic_state *PIC_UNUSED(pic), pic_value port)
+pic_feof(pic_state *pic, pic_value port)
 {
   struct file *fp = &port_ptr(pic, port)->file;
 
@@ -57,13 +57,36 @@ pic_feof(pic_state *PIC_UNUSED(pic), pic_value port)
 }
 
 int
-pic_ferror(pic_state *PIC_UNUSED(pic), pic_value port)
+pic_ferror(pic_state *pic, pic_value port)
 {
   struct file *fp = &port_ptr(pic, port)->file;
 
   return (fp->flag & FILE_ERR) != 0;
 }
 
+int
+pic_setvbuf(pic_state *pic, pic_value port, char *buf, int mode, size_t size)
+{
+  struct file *fp = &port_ptr(pic, port)->file;
+
+  fp->flag &= ~(FILE_UNBUF | FILE_LNBUF);
+  if (mode == PIC_IOLBF) {
+    fp->flag |= FILE_LNBUF;
+  } else if (mode == PIC_IONBF) {
+    fp->flag |= FILE_UNBUF;
+  }
+
+  if (buf == NULL) {
+    return 0;
+  }
+  if (size != PIC_BUFSIZ) {
+    return EOF;
+  }
+  fp->base = buf;
+  fp->flag |= FILE_SETBUF;
+  return 0;
+}
+
 static int
 fillbuf(pic_state *pic, struct file *fp)
 {
@@ -230,7 +253,7 @@ pic_fgets(pic_state *pic, char *s, int size, pic_value port)
 }
 
 int
-pic_ungetc(pic_state *PIC_UNUSED(pic), int c, pic_value port)
+pic_ungetc(pic_state *pic, int c, pic_value port)
 {
   struct file *fp = &port_ptr(pic, port)->file;
   unsigned char uc = c;
@@ -311,79 +334,7 @@ pic_fseek(pic_state *pic, pic_value port, long offset, int whence)
 int
 pic_vfprintf(pic_state *pic, pic_value port, const char *fmt, va_list ap)
 {
-  const char *p;
-  long start = pic_fseek(pic, port, 0, PIC_SEEK_CUR);
-
-  for (p = fmt; *p; p++) {
-    if (*p == '~') {
-      switch (*++p) {
-      default:
-        pic_fputc(pic, *(p-1), port);
-        break;
-      case '%':
-        pic_fputc(pic, '\n', port);
-        break;
-      case 'a':
-        pic_void(pic, pic_funcall(pic, "display", 2, va_arg(ap, pic_value), port));
-        break;
-      case 's':
-        pic_void(pic, pic_funcall(pic, "write", 2, va_arg(ap, pic_value), port));
-        break;
-      }
-      continue;
-    }
-    if (*p == '%') {
-      switch (*++p) {
-      case 'd':
-      case 'i': {
-        int ival = va_arg(ap, int);
-        pic_value str = pic_funcall(pic, "number->string", 1, pic_int_value(pic, ival));
-        pic_fputs(pic, pic_cstr(pic, str, 0), port);
-        break;
-      }
-      case 'f': {
-        double f = va_arg(ap, double);
-        pic_value str = pic_funcall(pic, "number->string", 1, pic_float_value(pic, f));
-        pic_fputs(pic, pic_cstr(pic, str, 0), port);
-        break;
-      }
-      case 'c': {
-        int ival = va_arg(ap, int);
-        pic_fputc(pic, ival, port);
-        break;
-      }
-      case 's': {
-        char *sval = va_arg(ap, char*);
-        pic_fputs(pic, sval, port);
-        break;
-      }
-      case 'p': {
-        static const char digits[] = "0123456789abcdef";
-        unsigned long vp = (unsigned long) va_arg(ap, void*);
-        char buf[sizeof vp * CHAR_BIT / 4 + 1];
-        size_t i;
-        for (i = 0; i < sizeof buf - 1; ++i) {
-          buf[sizeof buf - i - 2] = digits[vp % 16];
-          vp /= 16;
-        }
-        buf[i] = '\0';
-        pic_fputs(pic, "0x", port);
-        pic_fputs(pic, buf, port);
-        break;
-      }
-      case '%':
-        pic_fputc(pic, *(p-1), port);
-        break;
-      default:
-        pic_fputc(pic, '%', port);
-        pic_fputc(pic, *(p-1), port);
-        break;
-      }
-      continue;
-    }
-    pic_fputc(pic, *p, port);
-  }
-  return pic_fseek(pic, port, 0, PIC_SEEK_CUR) - start;
+  return pic_fputs(pic, pic_cstr(pic, pic_vstrf_value(pic, fmt, ap), NULL), port);
 }
 
 int
diff --git a/lib/string.c b/lib/string.c
index b59a7551..04012876 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -229,24 +229,67 @@ pic_strf_value(pic_state *pic, const char *fmt, ...)
   va_start(ap, fmt);
   str = pic_vstrf_value(pic, fmt, ap);
   va_end(ap);
-
   return str;
 }
 
 pic_value
 pic_vstrf_value(pic_state *pic, const char *fmt, va_list ap)
 {
-  pic_value str, port;
-  const char *buf;
-  int len;
+  pic_value str, str2;
+  const char *p;
 
-  port = pic_fmemopen(pic, NULL, 0, "w");
-
-  pic_vfprintf(pic, port, fmt, ap);
-  pic_fgetbuf(pic, port, &buf, &len);
-  str = pic_str_value(pic, buf, len);
-  pic_fclose(pic, port);
-  return str;
+  for (p = fmt; *p; p++) {
+    if (*p == '%')
+      break;
+  }
+  str = pic_str_value(pic, fmt, p - fmt);
+  if (*p == 0) {
+    return str;
+  }
+  p++;                          /* skip '%' */
+  switch (*p++) {
+  case '\0':
+    return pic_str_value(pic, fmt, p - fmt - 1);
+  case 'd':
+  case 'i': {
+    int i = va_arg(ap, int);
+    str2 = pic_funcall(pic, "number->string", 1, pic_int_value(pic, i));
+    break;
+  }
+  case 'f': {
+    double f = va_arg(ap, double);
+    str2 = pic_funcall(pic, "number->string", 1, pic_float_value(pic, f));
+    break;
+  }
+  case 'c': {
+    char c = (char) va_arg(ap, int);
+    str2 = pic_str_value(pic, &c, 1);
+    break;
+  }
+  case 's': {
+    char *sval = va_arg(ap, char*);
+    str2 = pic_cstr_value(pic, sval);
+    break;
+  }
+  case 'p': {
+    static const char digits[] = "0123456789abcdef";
+    static const size_t bufsiz = sizeof(long) * CHAR_BIT / 4;
+    unsigned long vp = (unsigned long) va_arg(ap, void*);
+    char buf[2 + bufsiz + 1] = "0x", *p = buf + 2;
+    size_t i;
+    for (i = 0; i < bufsiz; ++i) {
+      p[bufsiz - i - 2] = digits[vp % 16];
+      vp /= 16;
+    }
+    p[i] = '\0';
+    str2 = pic_cstr_value(pic, buf);
+    break;
+  }
+  case '%':
+    str2 = pic_str_value(pic, &p[-1], 1);
+    break;
+  }
+  return pic_str_cat(pic, str, pic_str_cat(pic, str2, pic_vstrf_value(pic, p, ap)));
 }
 
 int