diff --git a/extlib/benz/string.c b/extlib/benz/string.c
index de023afa..7d09eea5 100644
--- a/extlib/benz/string.c
+++ b/extlib/benz/string.c
@@ -5,509 +5,509 @@
 #include "picrin.h"
 
 struct pic_chunk {
-  char *str;
-  int refcnt;
-  size_t len;
-  char buf[1];
+	char *str;
+	int refcnt;
+	size_t len;
+	char buf[1];
 };
 
 struct pic_rope {
-  int refcnt;
-  size_t weight;
-  struct pic_chunk *chunk;
-  size_t offset;
-  struct pic_rope *left, *right;
+	int refcnt;
+	size_t weight;
+	struct pic_chunk *chunk;
+	size_t offset;
+	struct pic_rope *left, *right;
 };
 
 #define CHUNK_INCREF(c) do {                    \
-    (c)->refcnt++;                              \
-  } while (0)
+		(c)->refcnt++;                              \
+	} while (0)
 
 #define CHUNK_DECREF(c) do {                    \
-    struct pic_chunk *c_ = (c);                 \
-    if (! --c_->refcnt) {                       \
-      if (c_->str != c_->buf)                   \
-        pic_free(pic, c_->str);                 \
-      pic_free(pic, c_);                        \
-    }                                           \
-  } while (0)
+		struct pic_chunk *c_ = (c);                 \
+		if (! --c_->refcnt) {                       \
+			if (c_->str != c_->buf)                   \
+				pic_free(pic, c_->str);                 \
+			pic_free(pic, c_);                        \
+		}                                           \
+	} while (0)
 
 void
 pic_rope_incref(pic_state PIC_UNUSED(*pic), struct pic_rope *x) {
-  x->refcnt++;
+	x->refcnt++;
 }
 
 void
 pic_rope_decref(pic_state *pic, struct pic_rope *x) {
-  if (! --x->refcnt) {
-    if (x->chunk) {
-      CHUNK_DECREF(x->chunk);
-      pic_free(pic, x);
-      return;
-    }
-    pic_rope_decref(pic, x->left);
-    pic_rope_decref(pic, x->right);
-    pic_free(pic, x);
-  }
+	if (! --x->refcnt) {
+		if (x->chunk) {
+			CHUNK_DECREF(x->chunk);
+			pic_free(pic, x);
+			return;
+		}
+		pic_rope_decref(pic, x->left);
+		pic_rope_decref(pic, x->right);
+		pic_free(pic, x);
+	}
 }
 
 static struct pic_chunk *
 pic_make_chunk(pic_state *pic, const char *str, size_t len)
 {
-  struct pic_chunk *c;
+	struct pic_chunk *c;
 
-  c = pic_malloc(pic, sizeof(struct pic_chunk) + len);
-  c->refcnt = 1;
-  c->str = c->buf;
-  c->len = len;
-  c->buf[len] = 0;
-  memcpy(c->buf, str, len);
+	c = pic_malloc(pic, sizeof(struct pic_chunk) + len);
+	c->refcnt = 1;
+	c->str = c->buf;
+	c->len = len;
+	c->buf[len] = 0;
+	memcpy(c->buf, str, len);
 
-  return c;
+	return c;
 }
 
 static struct pic_rope *
 pic_make_rope(pic_state *pic, struct pic_chunk *c)
 {
-  struct pic_rope *x;
+	struct pic_rope *x;
 
-  x = pic_malloc(pic, sizeof(struct pic_rope));
-  x->refcnt = 1;
-  x->left = NULL;
-  x->right = NULL;
-  x->weight = c->len;
-  x->offset = 0;
-  x->chunk = c;                 /* delegate ownership */
+	x = pic_malloc(pic, sizeof(struct pic_rope));
+	x->refcnt = 1;
+	x->left = NULL;
+	x->right = NULL;
+	x->weight = c->len;
+	x->offset = 0;
+	x->chunk = c;                 /* delegate ownership */
 
-  return x;
+	return x;
 }
 
 static pic_str *
 pic_make_string(pic_state *pic, struct pic_rope *rope)
 {
-  pic_str *str;
+	pic_str *str;
 
-  str = (pic_str *)pic_obj_alloc(pic, sizeof(pic_str), PIC_TT_STRING);
-  str->rope = rope;             /* delegate ownership */
-  return str;
+	str = (pic_str *)pic_obj_alloc(pic, sizeof(pic_str), PIC_TT_STRING);
+	str->rope = rope;             /* delegate ownership */
+	return str;
 }
 
 static size_t
 rope_len(struct pic_rope *x)
 {
-  return x->weight;
+	return x->weight;
 }
 
 static char
 rope_at(struct pic_rope *x, size_t i)
 {
-  while (i < x->weight) {
-    if (x->chunk) {
-      return x->chunk->str[x->offset + i];
-    }
-    if (i < x->left->weight) {
-      x = x->left;
-    } else {
-      x = x->right;
-      i -= x->left->weight;
-    }
-  }
-  return -1;
+	while (i < x->weight) {
+		if (x->chunk) {
+			return x->chunk->str[x->offset + i];
+		}
+		if (i < x->left->weight) {
+			x = x->left;
+		} else {
+			x = x->right;
+			i -= x->left->weight;
+		}
+	}
+	return -1;
 }
 
 static struct pic_rope *
 rope_cat(pic_state *pic, struct pic_rope *x, struct pic_rope *y)
 {
-  struct pic_rope *z;
+	struct pic_rope *z;
 
-  z = pic_malloc(pic, sizeof(struct pic_rope));
-  z->refcnt = 1;
-  z->left = x;
-  z->right = y;
-  z->weight = x->weight + y->weight;
-  z->offset = 0;
-  z->chunk = NULL;
+	z = pic_malloc(pic, sizeof(struct pic_rope));
+	z->refcnt = 1;
+	z->left = x;
+	z->right = y;
+	z->weight = x->weight + y->weight;
+	z->offset = 0;
+	z->chunk = NULL;
 
-  pic_rope_incref(pic, x);
-  pic_rope_incref(pic, y);
+	pic_rope_incref(pic, x);
+	pic_rope_incref(pic, y);
 
-  return z;
+	return z;
 }
 
 static struct pic_rope *
 rope_sub(pic_state *pic, struct pic_rope *x, size_t i, size_t j)
 {
-  assert(i <= j);
-  assert(j <= x->weight);
+	assert(i <= j);
+	assert(j <= x->weight);
 
-  if (i == 0 && x->weight == j) {
-    pic_rope_incref(pic, x);
-    return x;
-  }
+	if (i == 0 && x->weight == j) {
+		pic_rope_incref(pic, x);
+		return x;
+	}
 
-  if (x->chunk) {
-    struct pic_rope *y;
+	if (x->chunk) {
+		struct pic_rope *y;
 
-    y = pic_malloc(pic, sizeof(struct pic_rope));
-    y->refcnt = 1;
-    y->left = NULL;
-    y->right = NULL;
-    y->weight = j - i;
-    y->offset = x->offset + i;
-    y->chunk = x->chunk;
+		y = pic_malloc(pic, sizeof(struct pic_rope));
+		y->refcnt = 1;
+		y->left = NULL;
+		y->right = NULL;
+		y->weight = j - i;
+		y->offset = x->offset + i;
+		y->chunk = x->chunk;
 
-    CHUNK_INCREF(x->chunk);
+		CHUNK_INCREF(x->chunk);
 
-    return y;
-  }
+		return y;
+	}
 
-  if (j <= x->left->weight) {
-    return rope_sub(pic, x->left, i, j);
-  }
-  else if (x->left->weight <= i) {
-    return rope_sub(pic, x->right, i - x->left->weight, j - x->left->weight);
-  }
-  else {
-    struct pic_rope *r, *l;
+	if (j <= x->left->weight) {
+		return rope_sub(pic, x->left, i, j);
+	}
+	else if (x->left->weight <= i) {
+		return rope_sub(pic, x->right, i - x->left->weight, j - x->left->weight);
+	}
+	else {
+		struct pic_rope *r, *l;
 
-    l = rope_sub(pic, x->left, i, x->left->weight);
-    r = rope_sub(pic, x->right, 0, j - x->left->weight);
-    x = rope_cat(pic, l, r);
+		l = rope_sub(pic, x->left, i, x->left->weight);
+		r = rope_sub(pic, x->right, 0, j - x->left->weight);
+		x = rope_cat(pic, l, r);
 
-    pic_rope_decref(pic, l);
-    pic_rope_decref(pic, r);
+		pic_rope_decref(pic, l);
+		pic_rope_decref(pic, r);
 
-    return x;
-  }
+		return x;
+	}
 }
 
 static void
 flatten(pic_state *pic, struct pic_rope *x, struct pic_chunk *c, size_t offset)
 {
-  if (x->chunk) {
-    memcpy(c->str + offset, x->chunk->str + x->offset, x->weight);
-    CHUNK_DECREF(x->chunk);
+	if (x->chunk) {
+		memcpy(c->str + offset, x->chunk->str + x->offset, x->weight);
+		CHUNK_DECREF(x->chunk);
 
-    x->chunk = c;
-    x->offset = offset;
-    CHUNK_INCREF(c);
-    return;
-  }
-  flatten(pic, x->left, c, offset);
-  flatten(pic, x->right, c, offset + x->left->weight);
+		x->chunk = c;
+		x->offset = offset;
+		CHUNK_INCREF(c);
+		return;
+	}
+	flatten(pic, x->left, c, offset);
+	flatten(pic, x->right, c, offset + x->left->weight);
 
-  pic_rope_decref(pic, x->left);
-  pic_rope_decref(pic, x->right);
-  x->left = x->right = NULL;
-  x->chunk = c;
-  x->offset = offset;
-  CHUNK_INCREF(c);
+	pic_rope_decref(pic, x->left);
+	pic_rope_decref(pic, x->right);
+	x->left = x->right = NULL;
+	x->chunk = c;
+	x->offset = offset;
+	CHUNK_INCREF(c);
 }
 
 static const char *
 rope_cstr(pic_state *pic, struct pic_rope *x)
 {
-  struct pic_chunk *c;
+	struct pic_chunk *c;
 
-  if (x->chunk && x->offset == 0 && x->weight == x->chunk->len) {
-    return x->chunk->str;       /* reuse cached chunk */
-  }
+	if (x->chunk && x->offset == 0 && x->weight == x->chunk->len) {
+		return x->chunk->str;       /* reuse cached chunk */
+	}
 
-  c = pic_malloc(pic, sizeof(struct pic_chunk) + x->weight);
-  c->refcnt = 1;
-  c->len = x->weight;
-  c->str = c->buf;
-  c->str[c->len] = '\0';
+	c = pic_malloc(pic, sizeof(struct pic_chunk) + x->weight);
+	c->refcnt = 1;
+	c->len = x->weight;
+	c->str = c->buf;
+	c->str[c->len] = '\0';
 
-  flatten(pic, x, c, 0);
+	flatten(pic, x, c, 0);
 
-  CHUNK_DECREF(c);
-  return c->str;
+	CHUNK_DECREF(c);
+	return c->str;
 }
 
 pic_str *
 pic_make_str(pic_state *pic, const char *str, int len)
 {
-  if (str == NULL && len > 0) {
-    pic_errorf(pic, "zero length specified against NULL ptr");
-  }
-  return pic_make_string(pic, pic_make_rope(pic, pic_make_chunk(pic, str, len)));
+	if (str == NULL && len > 0) {
+		pic_errorf(pic, "zero length specified against NULL ptr");
+	}
+	return pic_make_string(pic, pic_make_rope(pic, pic_make_chunk(pic, str, len)));
 }
 
 pic_str *
 pic_make_str_cstr(pic_state *pic, const char *cstr)
 {
-  return pic_make_str(pic, cstr, strlen(cstr));
+	return pic_make_str(pic, cstr, strlen(cstr));
 }
 
 int
 pic_str_len(pic_str *str)
 {
-  return rope_len(str->rope);
+	return rope_len(str->rope);
 }
 
 char
 pic_str_ref(pic_state *pic, pic_str *str, int i)
 {
-  int c;
+	int c;
 
-  c = rope_at(str->rope, i);
-  if (c == -1) {
-    pic_errorf(pic, "index out of range %d", i);
-  }
-  return (char)c;
+	c = rope_at(str->rope, i);
+	if (c == -1) {
+		pic_errorf(pic, "index out of range %d", i);
+	}
+	return (char)c;
 }
 
 pic_str *
 pic_str_cat(pic_state *pic, pic_str *a, pic_str *b)
 {
-  return pic_make_string(pic, rope_cat(pic, a->rope, b->rope));
+	return pic_make_string(pic, rope_cat(pic, a->rope, b->rope));
 }
 
 pic_str *
 pic_str_sub(pic_state *pic, pic_str *str, int s, int e)
 {
-  return pic_make_string(pic, rope_sub(pic, str->rope, s, e));
+	return pic_make_string(pic, rope_sub(pic, str->rope, s, e));
 }
 
 int
 pic_str_cmp(pic_state *pic, pic_str *str1, pic_str *str2)
 {
-  return strcmp(pic_str_cstr(pic, str1), pic_str_cstr(pic, str2));
+	return strcmp(pic_str_cstr(pic, str1), pic_str_cstr(pic, str2));
 }
 
 const char *
 pic_str_cstr(pic_state *pic, pic_str *str)
 {
-  return rope_cstr(pic, str->rope);
+	return rope_cstr(pic, str->rope);
 }
 
 pic_value
 pic_xvfformat(pic_state *pic, xFILE *file, const char *fmt, va_list ap)
 {
-  char c;
-  pic_value irrs = pic_nil_value();
+	char c;
+	pic_value irrs = pic_nil_value();
 
-  while ((c = *fmt++)) {
-    switch (c) {
-    default:
-      xfputc(pic, c, file);
-      break;
-    case '%':
-      c = *fmt++;
-      if (! c)
-        goto exit;
-      switch (c) {
-      default:
-        xfputc(pic, c, file);
-        break;
-      case '%':
-        xfputc(pic, '%', file);
-        break;
-      case 'c':
-        xfprintf(pic, file, "%c", va_arg(ap, int));
-        break;
-      case 's':
-        xfprintf(pic, file, "%s", va_arg(ap, const char *));
-        break;
-      case 'd':
-        xfprintf(pic, file, "%d", va_arg(ap, int));
-        break;
-      case 'p':
-        xfprintf(pic, file, "%p", va_arg(ap, void *));
-        break;
-      case 'f':
-        xfprintf(pic, file, "%f", va_arg(ap, double));
-        break;
-      }
-      break;
-    case '~':
-      c = *fmt++;
-      if (! c)
-        goto exit;
-      switch (c) {
-      default:
-        xfputc(pic, c, file);
-        break;
-      case '~':
-        xfputc(pic, '~', file);
-        break;
-      case '%':
-        xfputc(pic, '\n', file);
-        break;
-      case 'a':
-        irrs = pic_cons(pic, pic_fdisplay(pic, va_arg(ap, pic_value), file), irrs);
-        break;
-      case 's':
-        irrs = pic_cons(pic, pic_fwrite(pic, va_arg(ap, pic_value), file), irrs);
-        break;
-      }
-      break;
-    }
-  }
+	while ((c = *fmt++)) {
+		switch (c) {
+		default:
+			xfputc(pic, c, file);
+			break;
+		case '%':
+			c = *fmt++;
+			if (! c)
+				goto exit;
+			switch (c) {
+			default:
+				xfputc(pic, c, file);
+				break;
+			case '%':
+				xfputc(pic, '%', file);
+				break;
+			case 'c':
+				xfprintf(pic, file, "%c", va_arg(ap, int));
+				break;
+			case 's':
+				xfprintf(pic, file, "%s", va_arg(ap, const char *));
+				break;
+			case 'd':
+				xfprintf(pic, file, "%d", va_arg(ap, int));
+				break;
+			case 'p':
+				xfprintf(pic, file, "%p", va_arg(ap, void *));
+				break;
+			case 'f':
+				xfprintf(pic, file, "%f", va_arg(ap, double));
+				break;
+			}
+			break;
+		case '~':
+			c = *fmt++;
+			if (! c)
+				goto exit;
+			switch (c) {
+			default:
+				xfputc(pic, c, file);
+				break;
+			case '~':
+				xfputc(pic, '~', file);
+				break;
+			case '%':
+				xfputc(pic, '\n', file);
+				break;
+			case 'a':
+				irrs = pic_cons(pic, pic_fdisplay(pic, va_arg(ap, pic_value), file), irrs);
+				break;
+			case 's':
+				irrs = pic_cons(pic, pic_fwrite(pic, va_arg(ap, pic_value), file), irrs);
+				break;
+			}
+			break;
+		}
+	}
  exit:
 
-  return pic_reverse(pic, irrs);
+	return pic_reverse(pic, irrs);
 }
 
 pic_value
 pic_xvformat(pic_state *pic, const char *fmt, va_list ap)
 {
-  struct pic_port *port;
-  pic_value irrs;
+	struct pic_port *port;
+	pic_value irrs;
 
-  port = pic_open_output_string(pic);
+	port = pic_open_output_string(pic);
 
-  irrs = pic_xvfformat(pic, port->file, fmt, ap);
-  irrs = pic_cons(pic, pic_obj_value(pic_get_output_string(pic, port)), irrs);
+	irrs = pic_xvfformat(pic, port->file, fmt, ap);
+	irrs = pic_cons(pic, pic_obj_value(pic_get_output_string(pic, port)), irrs);
 
-  pic_close_port(pic, port);
-  return irrs;
+	pic_close_port(pic, port);
+	return irrs;
 }
 
 pic_value
 pic_xformat(pic_state *pic, const char *fmt, ...)
 {
-  va_list ap;
-  pic_value objs;
+	va_list ap;
+	pic_value objs;
 
-  va_start(ap, fmt);
-  objs = pic_xvformat(pic, fmt, ap);
-  va_end(ap);
+	va_start(ap, fmt);
+	objs = pic_xvformat(pic, fmt, ap);
+	va_end(ap);
 
-  return objs;
+	return objs;
 }
 
 void
 pic_vfformat(pic_state *pic, xFILE *file, const char *fmt, va_list ap)
 {
-  pic_xvfformat(pic, file, fmt, ap);
+	pic_xvfformat(pic, file, fmt, ap);
 }
 
 pic_str *
 pic_vformat(pic_state *pic, const char *fmt, va_list ap)
 {
-  struct pic_port *port;
-  pic_str *str;
+	struct pic_port *port;
+	pic_str *str;
 
-  port = pic_open_output_string(pic);
+	port = pic_open_output_string(pic);
 
-  pic_vfformat(pic, port->file, fmt, ap);
-  str = pic_get_output_string(pic, port);
+	pic_vfformat(pic, port->file, fmt, ap);
+	str = pic_get_output_string(pic, port);
 
-  pic_close_port(pic, port);
-  return str;
+	pic_close_port(pic, port);
+	return str;
 }
 
 pic_str *
 pic_format(pic_state *pic, const char *fmt, ...)
 {
-  va_list ap;
-  pic_str *str;
+	va_list ap;
+	pic_str *str;
 
-  va_start(ap, fmt);
-  str = pic_vformat(pic, fmt, ap);
-  va_end(ap);
+	va_start(ap, fmt);
+	str = pic_vformat(pic, fmt, ap);
+	va_end(ap);
 
-  return str;
+	return str;
 }
 
 static pic_value
 pic_str_string_p(pic_state *pic)
 {
-  pic_value v;
+	pic_value v;
 
-  pic_get_args(pic, "o", &v);
+	pic_get_args(pic, "o", &v);
 
-  return pic_bool_value(pic_str_p(v));
+	return pic_bool_value(pic_str_p(v));
 }
 
 static pic_value
 pic_str_string(pic_state *pic)
 {
-  int argc, i;
-  pic_value *argv;
-  pic_str *str;
-  char *buf;
+	int argc, i;
+	pic_value *argv;
+	pic_str *str;
+	char *buf;
 
-  pic_get_args(pic, "*", &argc, &argv);
+	pic_get_args(pic, "*", &argc, &argv);
 
-  buf = pic_malloc(pic, argc);
+	buf = pic_malloc(pic, argc);
 
-  for (i = 0; i < argc; ++i) {
-    pic_assert_type(pic, argv[i], char);
-    buf[i] = pic_char(argv[i]);
-  }
+	for (i = 0; i < argc; ++i) {
+		pic_assert_type(pic, argv[i], char);
+		buf[i] = pic_char(argv[i]);
+	}
 
-  str = pic_make_str(pic, buf, argc);
-  pic_free(pic, buf);
+	str = pic_make_str(pic, buf, argc);
+	pic_free(pic, buf);
 
-  return pic_obj_value(str);
+	return pic_obj_value(str);
 }
 
 static pic_value
 pic_str_make_string(pic_state *pic)
 {
-  int len;
-  char c = ' ';
-  char *buf;
-  pic_value ret;
+	int len;
+	char c = ' ';
+	char *buf;
+	pic_value ret;
 
-  pic_get_args(pic, "i|c", &len, &c);
+	pic_get_args(pic, "i|c", &len, &c);
 
-  buf = pic_malloc(pic, len);
-  memset(buf, c, len);
+	buf = pic_malloc(pic, len);
+	memset(buf, c, len);
 
-  ret = pic_obj_value(pic_make_str(pic, buf, len));
+	ret = pic_obj_value(pic_make_str(pic, buf, len));
 
-  pic_free(pic, buf);
-  return ret;
+	pic_free(pic, buf);
+	return ret;
 }
 
 static pic_value
 pic_str_string_length(pic_state *pic)
 {
-  pic_str *str;
+	pic_str *str;
 
-  pic_get_args(pic, "s", &str);
+	pic_get_args(pic, "s", &str);
 
-  return pic_int_value(pic_str_len(str));
+	return pic_int_value(pic_str_len(str));
 }
 
 static pic_value
 pic_str_string_ref(pic_state *pic)
 {
-  pic_str *str;
-  int k;
+	pic_str *str;
+	int k;
 
-  pic_get_args(pic, "si", &str, &k);
+	pic_get_args(pic, "si", &str, &k);
 
-  return pic_char_value(pic_str_ref(pic, str, k));
+	return pic_char_value(pic_str_ref(pic, str, k));
 }
 
 #define DEFINE_STRING_CMP(name, op)                                     \
-  static pic_value                                                      \
-  pic_str_string_##name(pic_state *pic)                                 \
-  {                                                                     \
-    int argc, i;                                                     \
-    pic_value *argv;                                                    \
-                                                                        \
-    pic_get_args(pic, "*", &argc, &argv);                               \
-                                                                        \
-    if (argc < 1 || ! pic_str_p(argv[0])) {                             \
-      return pic_false_value();                                         \
-    }                                                                   \
-                                                                        \
-    for (i = 1; i < argc; ++i) {                                        \
-      if (! pic_str_p(argv[i])) {                                       \
+	static pic_value                                                      \
+	pic_str_string_##name(pic_state *pic)                                 \
+	{                                                                     \
+		int argc, i;                                                     \
+		pic_value *argv;                                                    \
+																																				\
+		pic_get_args(pic, "*", &argc, &argv);                               \
+																																				\
+		if (argc < 1 || ! pic_str_p(argv[0])) {                             \
+			return pic_false_value();                                         \
+		}                                                                   \
+																																				\
+		for (i = 1; i < argc; ++i) {                                        \
+			if (! pic_str_p(argv[i])) {                                       \
 	return pic_false_value();                                       \
-      }                                                                 \
-      if (! (pic_str_cmp(pic, pic_str_ptr(argv[i-1]), pic_str_ptr(argv[i])) op 0)) { \
+			}                                                                 \
+			if (! (pic_str_cmp(pic, pic_str_ptr(argv[i-1]), pic_str_ptr(argv[i])) op 0)) { \
 	return pic_false_value();                                       \
-      }                                                                 \
-    }                                                                   \
-    return pic_true_value();                                            \
-  }
+			}                                                                 \
+		}                                                                   \
+		return pic_true_value();                                            \
+	}
 
 DEFINE_STRING_CMP(eq, ==)
 DEFINE_STRING_CMP(lt, <)
@@ -518,200 +518,218 @@ DEFINE_STRING_CMP(ge, >=)
 static pic_value
 pic_str_string_copy(pic_state *pic)
 {
-  pic_str *str;
-  int n, start, end;
+	pic_str *str;
+	int n, start, end, len;
 
-  n = pic_get_args(pic, "s|ii", &str, &start, &end);
+	n = pic_get_args(pic, "s|ii", &str, &start, &end);
 
-  switch (n) {
-  case 1:
-    start = 0;
-  case 2:
-    end = pic_str_len(str);
-  }
+	len = pic_str_len(str);
 
-  return pic_obj_value(pic_str_sub(pic, str, start, end));
+	switch (n) {
+	case 1:
+		start = 0;
+	case 2:
+		end = len;
+	}
+
+#if 0
+#if 0
+	if (start < 0) start = 0; /* should an error be reported? */
+	if (end > len) end = len; /* should an error be reported? */
+#else
+	if ((start < 0) || (end < 0) || (start > len) || (end > len))
+		pic_errorf(pic, "string-copy: invalid index");
+#endif
+	if (end < start) /* surely this is an error!? */
+		pic_errorf(pic, "string-copy: start index > end index");
+#else
+	/* simplest version to catch all cases as errors */
+	if ((start < 0) || (end > len) || (end < start))
+		pic_errorf(pic, "string-copy: invalid index");
+#endif
+
+	return pic_obj_value(pic_str_sub(pic, str, start, end));
 }
 
 static pic_value
 pic_str_string_append(pic_state *pic)
 {
-  int argc, i;
-  pic_value *argv;
-  pic_str *str;
+	int argc, i;
+	pic_value *argv;
+	pic_str *str;
 
-  pic_get_args(pic, "*", &argc, &argv);
+	pic_get_args(pic, "*", &argc, &argv);
 
-  str = pic_make_str(pic, NULL, 0);
-  for (i = 0; i < argc; ++i) {
-    if (! pic_str_p(argv[i])) {
-      pic_errorf(pic, "type error");
-    }
-    str = pic_str_cat(pic, str, pic_str_ptr(argv[i]));
-  }
-  return pic_obj_value(str);
+	str = pic_make_str(pic, NULL, 0);
+	for (i = 0; i < argc; ++i) {
+		if (! pic_str_p(argv[i])) {
+			pic_errorf(pic, "type error");
+		}
+		str = pic_str_cat(pic, str, pic_str_ptr(argv[i]));
+	}
+	return pic_obj_value(str);
 }
 
 static pic_value
 pic_str_string_map(pic_state *pic)
 {
-  struct pic_proc *proc;
-  pic_value *argv, vals, val;
-  int argc, i, len, j;
-  pic_str *str;
-  char *buf;
+	struct pic_proc *proc;
+	pic_value *argv, vals, val;
+	int argc, i, len, j;
+	pic_str *str;
+	char *buf;
 
-  pic_get_args(pic, "l*", &proc, &argc, &argv);
+	pic_get_args(pic, "l*", &proc, &argc, &argv);
 
-  if (argc == 0) {
-    pic_errorf(pic, "string-map: one or more strings expected, but got zero");
-  } else {
-    pic_assert_type(pic, argv[0], str);
-    len = pic_str_len(pic_str_ptr(argv[0]));
-  }
-  for (i = 1; i < argc; ++i) {
-    pic_assert_type(pic, argv[i], str);
+	if (argc == 0) {
+		pic_errorf(pic, "string-map: one or more strings expected, but got zero");
+	} else {
+		pic_assert_type(pic, argv[0], str);
+		len = pic_str_len(pic_str_ptr(argv[0]));
+	}
+	for (i = 1; i < argc; ++i) {
+		pic_assert_type(pic, argv[i], str);
 
-    len = len < pic_str_len(pic_str_ptr(argv[i]))
-      ? len
-      : pic_str_len(pic_str_ptr(argv[i]));
-  }
-  buf = pic_malloc(pic, len);
+		len = len < pic_str_len(pic_str_ptr(argv[i]))
+			? len
+			: pic_str_len(pic_str_ptr(argv[i]));
+	}
+	buf = pic_malloc(pic, len);
 
-  pic_try {
-    for (i = 0; i < len; ++i) {
-      vals = pic_nil_value();
-      for (j = 0; j < argc; ++j) {
-        pic_push(pic, pic_char_value(pic_str_ref(pic, pic_str_ptr(argv[j]), i)), vals);
-      }
-      val = pic_apply_list(pic, proc, vals);
+	pic_try {
+		for (i = 0; i < len; ++i) {
+			vals = pic_nil_value();
+			for (j = 0; j < argc; ++j) {
+				pic_push(pic, pic_char_value(pic_str_ref(pic, pic_str_ptr(argv[j]), i)), vals);
+			}
+			val = pic_apply_list(pic, proc, vals);
 
-      pic_assert_type(pic, val, char);
-      buf[i] = pic_char(val);
-    }
-    str = pic_make_str(pic, buf, len);
-  }
-  pic_catch {
-    pic_free(pic, buf);
-    pic_raise(pic, pic->err);
-  }
+			pic_assert_type(pic, val, char);
+			buf[i] = pic_char(val);
+		}
+		str = pic_make_str(pic, buf, len);
+	}
+	pic_catch {
+		pic_free(pic, buf);
+		pic_raise(pic, pic->err);
+	}
 
-  pic_free(pic, buf);
+	pic_free(pic, buf);
 
-  return pic_obj_value(str);
+	return pic_obj_value(str);
 }
 
 static pic_value
 pic_str_string_for_each(pic_state *pic)
 {
-  struct pic_proc *proc;
-  int argc, len, i, j;
-  pic_value *argv, vals;
+	struct pic_proc *proc;
+	int argc, len, i, j;
+	pic_value *argv, vals;
 
-  pic_get_args(pic, "l*", &proc, &argc, &argv);
+	pic_get_args(pic, "l*", &proc, &argc, &argv);
 
-  if (argc == 0) {
-    pic_errorf(pic, "string-map: one or more strings expected, but got zero");
-  } else {
-    pic_assert_type(pic, argv[0], str);
-    len = pic_str_len(pic_str_ptr(argv[0]));
-  }
-  for (i = 1; i < argc; ++i) {
-    pic_assert_type(pic, argv[i], str);
+	if (argc == 0) {
+		pic_errorf(pic, "string-map: one or more strings expected, but got zero");
+	} else {
+		pic_assert_type(pic, argv[0], str);
+		len = pic_str_len(pic_str_ptr(argv[0]));
+	}
+	for (i = 1; i < argc; ++i) {
+		pic_assert_type(pic, argv[i], str);
 
-    len = len < pic_str_len(pic_str_ptr(argv[i]))
-      ? len
-      : pic_str_len(pic_str_ptr(argv[i]));
-  }
+		len = len < pic_str_len(pic_str_ptr(argv[i]))
+			? len
+			: pic_str_len(pic_str_ptr(argv[i]));
+	}
 
-  for (i = 0; i < len; ++i) {
-    vals = pic_nil_value();
-    for (j = 0; j < argc; ++j) {
-      pic_push(pic, pic_char_value(pic_str_ref(pic, pic_str_ptr(argv[j]), i)), vals);
-    }
-    pic_apply_list(pic, proc, vals);
-  }
+	for (i = 0; i < len; ++i) {
+		vals = pic_nil_value();
+		for (j = 0; j < argc; ++j) {
+			pic_push(pic, pic_char_value(pic_str_ref(pic, pic_str_ptr(argv[j]), i)), vals);
+		}
+		pic_apply_list(pic, proc, vals);
+	}
 
-  return pic_undef_value();
+	return pic_undef_value();
 }
 
 static pic_value
 pic_str_list_to_string(pic_state *pic)
 {
-  pic_str *str;
-  pic_value list, e, it;
-  int i;
-  char *buf;
+	pic_str *str;
+	pic_value list, e, it;
+	int i;
+	char *buf;
 
-  pic_get_args(pic, "o", &list);
+	pic_get_args(pic, "o", &list);
 
-  if (pic_length(pic, list) == 0) {
-    return pic_obj_value(pic_make_str(pic, NULL, 0));
-  }
+	if (pic_length(pic, list) == 0) {
+		return pic_obj_value(pic_make_str(pic, NULL, 0));
+	}
 
-  buf = pic_malloc(pic, pic_length(pic, list));
+	buf = pic_malloc(pic, pic_length(pic, list));
 
-  pic_try {
-    i = 0;
-    pic_for_each (e, list, it) {
-      pic_assert_type(pic, e, char);
+	pic_try {
+		i = 0;
+		pic_for_each (e, list, it) {
+			pic_assert_type(pic, e, char);
 
-      buf[i++] = pic_char(e);
-    }
+			buf[i++] = pic_char(e);
+		}
 
-    str = pic_make_str(pic, buf, i);
-  }
-  pic_catch {
-    pic_free(pic, buf);
-    pic_raise(pic, pic->err);
-  }
-  pic_free(pic, buf);
+		str = pic_make_str(pic, buf, i);
+	}
+	pic_catch {
+		pic_free(pic, buf);
+		pic_raise(pic, pic->err);
+	}
+	pic_free(pic, buf);
 
-  return pic_obj_value(str);
+	return pic_obj_value(str);
 }
 
 static pic_value
 pic_str_string_to_list(pic_state *pic)
 {
-  pic_str *str;
-  pic_value list;
-  int n, start, end, i;
+	pic_str *str;
+	pic_value list;
+	int n, start, end, i;
 
-  n = pic_get_args(pic, "s|ii", &str, &start, &end);
+	n = pic_get_args(pic, "s|ii", &str, &start, &end);
 
-  switch (n) {
-  case 1:
-    start = 0;
-  case 2:
-    end = pic_str_len(str);
-  }
+	switch (n) {
+	case 1:
+		start = 0;
+	case 2:
+		end = pic_str_len(str);
+	}
 
-  list = pic_nil_value();
+	list = pic_nil_value();
 
-  for (i = start; i < end; ++i) {
-    pic_push(pic, pic_char_value(pic_str_ref(pic, str, i)), list);
-  }
-  return pic_reverse(pic, list);
+	for (i = start; i < end; ++i) {
+		pic_push(pic, pic_char_value(pic_str_ref(pic, str, i)), list);
+	}
+	return pic_reverse(pic, list);
 }
 
 void
 pic_init_str(pic_state *pic)
 {
-  pic_defun(pic, "string?", pic_str_string_p);
-  pic_defun(pic, "string", pic_str_string);
-  pic_defun(pic, "make-string", pic_str_make_string);
-  pic_defun(pic, "string-length", pic_str_string_length);
-  pic_defun(pic, "string-ref", pic_str_string_ref);
-  pic_defun(pic, "string-copy", pic_str_string_copy);
-  pic_defun(pic, "string-append", pic_str_string_append);
-  pic_defun(pic, "string-map", pic_str_string_map);
-  pic_defun(pic, "string-for-each", pic_str_string_for_each);
-  pic_defun(pic, "list->string", pic_str_list_to_string);
-  pic_defun(pic, "string->list", pic_str_string_to_list);
+	pic_defun(pic, "string?", pic_str_string_p);
+	pic_defun(pic, "string", pic_str_string);
+	pic_defun(pic, "make-string", pic_str_make_string);
+	pic_defun(pic, "string-length", pic_str_string_length);
+	pic_defun(pic, "string-ref", pic_str_string_ref);
+	pic_defun(pic, "string-copy", pic_str_string_copy);
+	pic_defun(pic, "string-append", pic_str_string_append);
+	pic_defun(pic, "string-map", pic_str_string_map);
+	pic_defun(pic, "string-for-each", pic_str_string_for_each);
+	pic_defun(pic, "list->string", pic_str_list_to_string);
+	pic_defun(pic, "string->list", pic_str_string_to_list);
 
-  pic_defun(pic, "string=?", pic_str_string_eq);
-  pic_defun(pic, "string<?", pic_str_string_lt);
-  pic_defun(pic, "string>?", pic_str_string_gt);
-  pic_defun(pic, "string<=?", pic_str_string_le);
-  pic_defun(pic, "string>=?", pic_str_string_ge);
+	pic_defun(pic, "string=?", pic_str_string_eq);
+	pic_defun(pic, "string<?", pic_str_string_lt);
+	pic_defun(pic, "string>?", pic_str_string_gt);
+	pic_defun(pic, "string<=?", pic_str_string_le);
+	pic_defun(pic, "string>=?", pic_str_string_ge);
 }