diff --git a/lib/chibi/json-test.sld b/lib/chibi/json-test.sld
index dab39d64..e3f22631 100644
--- a/lib/chibi/json-test.sld
+++ b/lib/chibi/json-test.sld
@@ -4,13 +4,14 @@
   (export run-tests)
   (begin
     (define (run-tests)
-      (test-begin "json-parse")
-      (test 1 (parse-json "1"))
-      (test 1.5 (parse-json "1.5"))
-      (test 1000.0 (parse-json "1e3"))
-      (test "á" (parse-json "\"\\u00e1\""))
-      (test "𐐷" (parse-json "\"\\uD801\\uDC37\""))
-      (test "😐" (parse-json "\"\\uD83D\\uDE10\""))
+      (test-begin "json")
+      (test-begin "string->json")
+      (test 1 (string->json "1"))
+      (test 1.5 (string->json "1.5"))
+      (test 1000.0 (string->json "1e3"))
+      (test "á" (string->json "\"\\u00e1\""))
+      (test "𐐷" (string->json "\"\\uD801\\uDC37\""))
+      (test "😐" (string->json "\"\\uD83D\\uDE10\""))
       (test '((glossary
                (title . "example glossary")
                (GlossDiv
@@ -26,7 +27,7 @@
                    (para . "A meta-markup language, used to create markup languages such as DocBook.")
                    (GlossSeeAlso . #("GML" "XML")))
                   (GlossSee . "markup"))))))
-          (parse-json "{
+          (string->json "{
     \"glossary\": {
         \"title\": \"example glossary\",
 		\"GlossDiv\": {
@@ -56,7 +57,7 @@
                  . #(((value . "New") (onclick . "CreateNewDoc()"))
                      ((value . "Open") (onclick . "OpenDoc()"))
                      ((value . "Close") (onclick . "CloseDoc()")))))))
-          (parse-json "{\"menu\": {
+          (string->json "{\"menu\": {
   \"id\": \"file\",
   \"value\": \"File\",
   \"popup\": {
@@ -68,15 +69,15 @@
   }
 }}"))
       (test-end)
-      (test-begin "json-unparse")
-      (test "1" (unparse-json 1))
-      (test "1.5" (unparse-json 1.5))
-      (test "1000" (unparse-json 1E3))
-      (test  "\"\\u00E1\"" (unparse-json "á"))
-      (test  "\"\\uD801\\uDC37\"" (unparse-json "𐐷"))
-      (test  "\"\\uD83D\\uDE10\"" (unparse-json "😐"))
+      (test-begin "json->string")
+      (test "1" (json->string 1))
+      (test "1.5" (json->string 1.5))
+      (test "1000" (json->string 1E3))
+      (test  "\"\\u00E1\"" (json->string "á"))
+      (test  "\"\\uD801\\uDC37\"" (json->string "𐐷"))
+      (test  "\"\\uD83D\\uDE10\"" (json->string "😐"))
       (test "{\"menu\":{\"id\":\"file\",\"value\":\"File\",\"popup\":{\"menuitem\":[{\"value\":\"New\",\"onclick\":\"CreateNewDoc()\"},{\"value\":\"Open\",\"onclick\":\"OpenDoc()\"},{\"value\":\"Close\",\"onclick\":\"CloseDoc()\"}]}}}"
-       (unparse-json '((menu
+       (json->string '((menu
                         (id . "file")
                         (value . "File")
                         (popup
@@ -85,7 +86,7 @@
                               ((value . "Open") (onclick . "OpenDoc()"))
                               ((value . "Close") (onclick . "CloseDoc()")))))))))
       (test "{\"glossary\":{\"title\":\"example glossary\",\"GlossDiv\":{\"title\":\"S\",\"GlossList\":{\"GlossEntry\":{\"ID\":\"SGML\",\"SortAs\":\"SGML\",\"GlossTerm\":\"Standard Generalized Markup Language\",\"Acronym\":\"SGML\",\"Abbrev\":\"ISO 8879:1986\",\"GlossDef\":{\"para\":\"A meta-markup language, used to create markup languages such as DocBook.\",\"GlossSeeAlso\":[\"GML\",\"XML\"]},\"GlossSee\":\"markup\"}}}}}"
-       (unparse-json '((glossary
+       (json->string '((glossary
                (title . "example glossary")
                (GlossDiv
                 (title . "S")
@@ -100,4 +101,6 @@
                    (para . "A meta-markup language, used to create markup languages such as DocBook.")
                    (GlossSeeAlso . #("GML" "XML")))
                   (GlossSee . "markup"))))))))
-      (test-end))))
+      (test-end)
+      (test-end)
+      )))
diff --git a/lib/chibi/json.c b/lib/chibi/json.c
index c289f698..badd5338 100644
--- a/lib/chibi/json.c
+++ b/lib/chibi/json.c
@@ -1,5 +1,5 @@
-/*  json.c -- fast json parser and unparser                  */
-/*  Copyright (c) 2019 Alex Shinn.      All rights reserved. */
+/*  json.c -- fast json I/O                                  */
+/*  Copyright (c) 2020 Alex Shinn.      All rights reserved. */
 /*  Copyright (c) 2020 Ekaitz Zarraga.  All rights reserved. */
 /*  BSD-style license: http://synthcode.com/license.txt      */
 
@@ -9,18 +9,23 @@ static int digit_value (int c) {
   return (((c)<='9') ? ((c) - '0') : ((sexp_tolower(c) - 'a') + 10));
 }
 
-sexp parse_json (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len);
+sexp json_read (sexp ctx, sexp self, sexp in);
 
-sexp sexp_json_parse_exception (sexp ctx, sexp self, const char* msg, sexp str, const int pos) {
-  sexp_gc_var2(res, tmp);
-  sexp_gc_preserve2(ctx, res, tmp);
-  tmp = sexp_list2(ctx, str, sexp_make_fixnum(pos));
-  res = sexp_user_exception(ctx, self, msg, tmp);
-  sexp_gc_release2(ctx);
+sexp sexp_json_read_exception (sexp ctx, sexp self, const char* msg, sexp in, sexp ir) {
+  sexp res;
+  sexp_gc_var4(sym, name, str, irr);
+  sexp_gc_preserve4(ctx, sym, name, str, irr);
+  name = (sexp_port_name(in) ? sexp_port_name(in) : SEXP_FALSE);
+  name = sexp_cons(ctx, name, sexp_make_fixnum(sexp_port_line(in)));
+  str = sexp_c_string(ctx, msg, -1);
+  irr = ((sexp_pairp(ir) || sexp_nullp(ir)) ? ir : sexp_list1(ctx, ir));
+  res = sexp_make_exception(ctx, sym = sexp_intern(ctx, "json-read", -1),
+                            str, irr, SEXP_FALSE, name);
+  sexp_gc_release4(ctx);
   return res;
 }
 
-sexp sexp_json_unparse_exception (sexp ctx, sexp self, const char* msg, sexp obj) {
+sexp sexp_json_write_exception (sexp ctx, sexp self, const char* msg, sexp obj) {
   sexp_gc_var2(res, tmp);
   sexp_gc_preserve2(ctx, res, tmp);
   tmp = sexp_list1(ctx, obj);
@@ -29,161 +34,171 @@ sexp sexp_json_unparse_exception (sexp ctx, sexp self, const char* msg, sexp obj
   return res;
 }
 
-sexp parse_json_number (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len) {
+sexp json_read_number (sexp ctx, sexp self, sexp in) {
   double res = 0, scale = 1;
-  int j = *i, sign = 1, inexactp = 0, scale_sign = 1;
-  if (s[j] == '+') {
-    ++j;
-  } else if (s[j] == '-') {
-    ++j;
+  int sign = 1, inexactp = 0, scale_sign = 1, ch;
+  ch = sexp_read_char(ctx, in);
+  if (ch == '+') {
+    ch = sexp_read_char(ctx, in);
+  } else if (ch == '-') {
+    ch = sexp_read_char(ctx, in);
     sign = -1;
   }
-  while (j < len && isdigit(s[j]))
-    res = res * 10 + s[j++] - '0';
-  if (j < len && s[j] == '.') {
+  for ( ; ch != EOF && isdigit(ch); ch = sexp_read_char(ctx, in))
+    res = res * 10 + ch - '0';
+  if (ch == '.') {
     inexactp = 1;
-    for (++j; j < len && isdigit(s[j]); scale *= 10)
-      res = res * 10 + s[j++] - '0';
+    for (ch = sexp_read_char(ctx, in); isdigit(ch); scale *= 10, ch = sexp_read_char(ctx, in))
+      res = res * 10 + ch - '0';
     res /= scale;
-  } else if (j < len && sexp_tolower(s[j]) == 'e') {
+  } else if (ch == 'e') {
     inexactp = 1;
-    if (j+1 < len) {
-      if (s[j+1] == '+') {
-        ++j;
-      } else if (s[j+1] == '-') {
-        ++j;
-        scale_sign = -1;
-      }
+    ch = sexp_read_char(ctx, in);
+    if (ch == '+') {
+      ch = sexp_read_char(ctx, in);
+    } else if (ch == '-') {
+      ch = sexp_read_char(ctx, in);
+      scale_sign = -1;
     }
-    for (++j, scale=0; j < len && isdigit(s[j]); )
-      scale = scale * 10 + s[j++] - '0';
+    for (scale=0; isdigit(ch); ch = sexp_read_char(ctx, in))
+      scale = scale * 10 + ch - '0';
     res *= pow(10.0, scale_sign * scale);
   }
-  *i = j;
+  if (ch != EOF) sexp_push_char(ctx, ch, in);
   return (inexactp || fabs(res) > SEXP_MAX_FIXNUM) ?
     sexp_make_flonum(ctx, sign * res) :
     sexp_make_fixnum(sign * res);  /* always return inexact? */
 }
 
-sexp parse_json_literal (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len, const char* name, int namelen, sexp value) {
-  sexp res;
-  if (strncasecmp(s+*i, name, namelen) == 0 && (*i+namelen >= len || !isalnum(s[*i+namelen]))) {
-    res = value;
-    *i += namelen;
-  } else {
-    res = sexp_json_parse_exception(ctx, self, "unexpected character in json at", str, *i);
-  }
-  return res;
+sexp json_read_literal (sexp ctx, sexp self, sexp in, char* name, sexp value) {
+  int ch;
+  for (++name; *name; )
+    if (*(name++) != (ch = sexp_read_char(ctx, in)))
+      sexp_json_read_exception(ctx, self, "unexpected character in json", in, sexp_make_character(ch));
+  return value;
 }
 
 #define USEQ_LEN 4
 
-long decode_useq(const char* s) {
-  long result = 0, i;
+long decode_useq(sexp ctx, sexp in) {
+  long result = 0, i, ch;
   for (i=0; i < USEQ_LEN; i++) {
-    if (!isxdigit(s[i]))
+    ch = sexp_read_char(ctx, in);
+    if (!isxdigit(ch)) {
+      sexp_push_char(ctx, ch, in);
       return -1;
-    result = (result << 4) + digit_value(s[i]);
+    }
+    result = (result << 4) + digit_value(ch);
   }
   return result;
 }
 
-sexp parse_json_string (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len) {
-  sexp_gc_var2(res, tmp);
-  sexp_gc_preserve2(ctx, res, tmp);
-  int from = *i, to = *i;
+#define INIT_STRING_BUFFER_SIZE 128
+
+sexp json_read_string (sexp ctx, sexp self, sexp in) {
+  sexp_sint_t size=INIT_STRING_BUFFER_SIZE;
+  char initbuf[INIT_STRING_BUFFER_SIZE];
+  char *buf=initbuf, *tmp;
+  int i=0, ch, len;
   long utfchar, utfchar2;
-  res = SEXP_NULL;
-  for ( ; s[to] != '"' && !sexp_exceptionp(res); ++to) {
-    if (to+1 >= len) {
-      res = sexp_json_parse_exception(ctx, self, "unterminated string in json started at", str, *i);
+  sexp res = SEXP_VOID;
+  for (ch = sexp_read_char(ctx, in); ch != '"'; ch = sexp_read_char(ctx, in)) {
+    if (ch == EOF) {
+      res = sexp_json_read_exception(ctx, self, "unterminated string in json", in, SEXP_NULL);
       break;
     }
-    if (s[to] == '\\') {
-      tmp = sexp_c_string(ctx, s+from, to-from);
-      res = sexp_stringp(res) ? sexp_list2(ctx, tmp, res) : sexp_cons(ctx, tmp, res);
-      switch (s[++to]) {
+    if (i+4 >= size) {       /* expand buffer w/ malloc(), later free() it */
+      tmp = (char*) sexp_malloc(size*2);
+      if (!tmp) {res = sexp_global(ctx, SEXP_G_OOM_ERROR); break;}
+      memcpy(tmp, buf, i);
+      if (size != INIT_STRING_BUFFER_SIZE) free(buf);
+      buf = tmp;
+      size *= 2;
+    }
+    if (ch == '\\') {
+      ch = sexp_read_char(ctx, in);
+      switch (ch) {
       case 'n':
-        tmp = sexp_c_string(ctx, "\n", -1);
-        res = sexp_cons(ctx, tmp, res);
-        from = to+1;
+        buf[i++] = '\n';
         break;
       case 't':
-        tmp = sexp_c_string(ctx, "\t", -1);
-        res = sexp_cons(ctx, tmp, res);
-        from = to+1;
+        buf[i++] = '\t';
         break;
       case 'u':
-        utfchar = decode_useq(s+to+1);
-        to += USEQ_LEN;
-        if (0xd800 <= utfchar && utfchar <= 0xdbff && s[to+1] == '\\' && s[to+2] == 'u') {
-          /* high surrogate followed by another unicode escape */
-          utfchar2 = decode_useq(s+to+3);
-          if (0xdc00 <= utfchar2 && utfchar2 <= 0xdfff) {
-            /* merge low surrogate (otherwise high is left unpaired) */
-            utfchar = 0x10000 + (((utfchar - 0xd800) << 10) | (utfchar2 - 0xdc00));
-            to += USEQ_LEN + 2;
+        utfchar = decode_useq(ctx, in);
+        if (0xd800 <= utfchar && utfchar <= 0xdbff) {
+          ch = sexp_read_char(ctx, in);
+          if (ch == '\\') {
+            ch = sexp_read_char(ctx, in);
+            if (ch == 'u') {
+              /* high surrogate followed by another unicode escape */
+              utfchar2 = decode_useq(ctx, in);
+              if (0xdc00 <= utfchar2 && utfchar2 <= 0xdfff) {
+                /* merge low surrogate (otherwise high is left unpaired) */
+                utfchar = 0x10000 + (((utfchar - 0xd800) << 10) | (utfchar2 - 0xdc00));
+              } else {
+                return sexp_json_read_exception(ctx, self, "invalid \\u sequence", in, SEXP_NULL);
+              }
+            } else {
+              sexp_push_char(ctx, ch, in);
+              sexp_push_char(ctx, '\\', in);
+            }
+          } else {
+            sexp_push_char(ctx, ch, in);
           }
         }
         if (utfchar < 0) {
-          res = sexp_json_parse_exception(ctx, self, "invalid \\u sequence at", str, to - USEQ_LEN);
+          return sexp_json_read_exception(ctx, self, "invalid \\u sequence", in, SEXP_NULL);
         } else {
-          tmp = sexp_make_string(ctx, sexp_make_fixnum(1), sexp_make_character(utfchar));
-          res = sexp_cons(ctx, tmp, res);
-          from = to + 1;
+          len = sexp_utf8_char_byte_count(utfchar);
+          sexp_utf8_encode_char((unsigned char*)buf + i, len, utfchar);
+          i += len;
         }
         break;
       default:
-        from = to;
+        buf[i++] = ch;
         break;
       }
+    } else {
+      buf[i++] = ch;
     }
   }
   if (!sexp_exceptionp(res)) {
-    tmp = sexp_c_string(ctx, s+from, to-from);
-    if (res == SEXP_NULL) {
-      res = tmp;
-    } else {
-      res = sexp_stringp(res) ? sexp_list2(ctx, tmp, res) : sexp_cons(ctx, tmp, res);
-      res = sexp_nreverse(ctx, res);
-      res = sexp_string_concatenate(ctx, res, SEXP_FALSE);
-    }
+    buf[i] = '\0';
+    res = sexp_c_string(ctx, buf, i);
+    if (sexp_stringp(res)) sexp_immutablep(res) = 1;
   }
-  *i = to+1;
-  sexp_gc_release2(ctx);
+  if (size != INIT_STRING_BUFFER_SIZE) free(buf);
   return res;
 }
 
-sexp parse_json_array (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len) {
+sexp json_read_array (sexp ctx, sexp self, sexp in) {
   sexp_gc_var2(res, tmp);
   sexp_gc_preserve2(ctx, res, tmp);
-  int j = *i;
-  int comma = 1;
+  int comma = 1, ch;
   res = SEXP_NULL;
   while (1) {
-    if (j >= len) {
-      res = sexp_json_parse_exception(ctx, self, "unterminated array in json started at", str, *i);
+    ch = sexp_read_char(ctx, in);
+    if (ch == EOF) {
+      res = sexp_json_read_exception(ctx, self, "unterminated array in json", in, SEXP_NULL);
       break;
-    } else if (s[j] == ']') {
+    } else if (ch == ']') {
       if (comma && res != SEXP_NULL) {
-        res = sexp_json_parse_exception(ctx, self, "missing value after comma in json array at", str, j);
+        res = sexp_json_read_exception(ctx, self, "missing value after comma in json", in, SEXP_NULL);
       } else {
         res = sexp_nreverse(ctx, res);
         res = sexp_list_to_vector(ctx, res);
       }
-      ++j;
       break;
-    } else if (s[j] == ',' && comma) {
-      res = sexp_json_parse_exception(ctx, self, "unexpected comma in json array at", str, j);
+    } else if (ch == ',' && comma) {
+      res = sexp_json_read_exception(ctx, self, "unexpected comma in json array", in, SEXP_NULL);
       break;
-    } else if (s[j] == ',') {
+    } else if (ch == ',') {
       comma = 1;
-      ++j;
-    } else if (isspace(s[j])) {
-      ++j;
-    } else {
+    } else if (!isspace(ch)) {
       if (comma) {
-        tmp = parse_json(ctx, self, str, s, &j, len);
+        sexp_push_char(ctx, ch, in);
+        tmp = json_read(ctx, self, in);
         if (sexp_exceptionp(tmp)) {
           res = tmp;
           break;
@@ -191,45 +206,41 @@ sexp parse_json_array (sexp ctx, sexp self, sexp str, const char* s, int* i, con
         res = sexp_cons(ctx, tmp, res);
         comma = 0;
       } else {
-        res = sexp_json_parse_exception(ctx, self, "unexpected value in json array at", str, j);
+        res = sexp_json_read_exception(ctx, self, "unexpected value in json array", in, SEXP_NULL);
         break;
       }
     }
   }
-  *i = j;
   sexp_gc_release2(ctx);
   return res;
 }
 
-sexp parse_json_object (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len) {
+sexp json_read_object (sexp ctx, sexp self, sexp in) {
   sexp_gc_var2(res, tmp);
   sexp_gc_preserve2(ctx, res, tmp);
-  int j = *i;
-  int comma = 1;
+  int comma = 1, ch;
   res = SEXP_NULL;
   while (1) {
-    if (j >= len) {
-      res = sexp_json_parse_exception(ctx, self, "unterminated object in json started at", str, *i);
+    ch = sexp_read_char(ctx, in);
+    if (ch == EOF) {
+      res = sexp_json_read_exception(ctx, self, "unterminated object in json", in, SEXP_NULL);
       break;
-    } else if (s[j] == '}') {
+    } else if (ch == '}') {
       if (comma && res != SEXP_NULL) {
-        res = sexp_json_parse_exception(ctx, self, "missing value after comma in json object at", str, j);
+        res = sexp_json_read_exception(ctx, self, "missing value after comma in json object", in, SEXP_NULL);
       } else {
         res = sexp_nreverse(ctx, res);
       }
-      ++j;
       break;
-    } else if (s[j] == ',' && comma) {
-      res = sexp_json_parse_exception(ctx, self, "unexpected comma in json object at", str, j);
+    } else if (ch == ',' && comma) {
+      res = sexp_json_read_exception(ctx, self, "unexpected comma in json object", in, SEXP_NULL);
       break;
-    } else if (s[j] == ',') {
+    } else if (ch == ',') {
       comma = 1;
-      ++j;
-    } else if (isspace(s[j])) {
-      ++j;
-    } else {
+    } else if (!isspace(ch)) {
       if (comma) {
-        tmp = parse_json(ctx, self, str, s, &j, len);
+        sexp_push_char(ctx, ch, in);
+        tmp = json_read(ctx, self, in);
         if (sexp_exceptionp(tmp)) {
           res = tmp;
           break;
@@ -237,14 +248,13 @@ sexp parse_json_object (sexp ctx, sexp self, sexp str, const char* s, int* i, co
           tmp = sexp_string_to_symbol(ctx, tmp);
         }
         tmp = sexp_cons(ctx, tmp, SEXP_VOID);
-        while (j < len && isspace(s[j]))
-          ++j;
-        if (s[j] != ':') {
-          res = sexp_json_parse_exception(ctx, self, "missing colon in json object at", str, j);
+        for (ch = sexp_read_char(ctx, in); isspace(ch); ch = sexp_read_char(ctx, in))
+          ;
+        if (ch != ':') {
+          res = sexp_json_read_exception(ctx, self, "missing colon in json object", in, sexp_make_character(ch));
           break;
         }
-        ++j;
-        sexp_cdr(tmp) = parse_json(ctx, self, str, s, &j, len);
+        sexp_cdr(tmp) = json_read(ctx, self, in);
         if (sexp_exceptionp(sexp_cdr(tmp))) {
           res = sexp_cdr(tmp);
           break;
@@ -252,324 +262,216 @@ sexp parse_json_object (sexp ctx, sexp self, sexp str, const char* s, int* i, co
         res = sexp_cons(ctx, tmp, res);
         comma = 0;
       } else {
-        res = sexp_json_parse_exception(ctx, self, "unexpected value in json object at", str, j);
+        res = sexp_json_read_exception(ctx, self, "unexpected value in json object", in, SEXP_NULL);
         break;
       }
     }
   }
-  *i = j;
   sexp_gc_release2(ctx);
   return res;
 }
 
-sexp parse_json (sexp ctx, sexp self, sexp str, const char* s, int* i, const int len) {
+sexp json_read (sexp ctx, sexp self, sexp in) {
   sexp res;
-  int j = *i;
-  while (j < len && isspace(s[j]))
-    ++j;
-  switch (s[j]) {
+  int ch = ' ';
+  while (isspace(ch))
+    ch = sexp_read_char(ctx, in);
+  switch (ch) {
   case '{':
-    ++j;
-    res = parse_json_object(ctx, self, str, s, &j, len);
+    res = json_read_object(ctx, self, in);
     break;
   case '[':
-    ++j;
-    res = parse_json_array(ctx, self, str, s, &j, len);
+    res = json_read_array(ctx, self, in);
     break;
   case '"':
-    ++j;
-    res = parse_json_string(ctx, self, str, s, &j, len);
+    res = json_read_string(ctx, self, in);
     break;
   case '-': case '+':
   case '0': case '1': case '2': case '3': case '4':
   case '5': case '6': case '7': case '8': case '9':
-    res = parse_json_number(ctx, self, str, s, &j, len);
+    sexp_push_char(ctx, ch, in);
+    res = json_read_number(ctx, self, in);
     break;
   case 'n': case 'N':
-    res = parse_json_literal(ctx, self, str, s, &j, len, "null", 4, SEXP_VOID);
+    res = json_read_literal(ctx, self, in, "null", SEXP_VOID);
     break;
   case 't': case 'T':
-    res = parse_json_literal(ctx, self, str, s, &j, len, "true", 4, SEXP_TRUE);
+    res = json_read_literal(ctx, self, in, "true", SEXP_TRUE);
     break;
   case 'f': case 'F':
-    res = parse_json_literal(ctx, self, str, s, &j, len, "false", 5, SEXP_FALSE);
+    res = json_read_literal(ctx, self, in, "false", SEXP_FALSE);
     break;
   case '}':
-    res = sexp_json_parse_exception(ctx, self, "unexpected closing brace in json at", str, j);
+    res = sexp_json_read_exception(ctx, self, "unexpected closing brace in json", in, SEXP_NULL);
     break;
   case ']':
-    res = sexp_json_parse_exception(ctx, self, "unexpected closing bracket in json at", str, j);
+    res = sexp_json_read_exception(ctx, self, "unexpected closing bracket in json", in, SEXP_NULL);
     break;
   default:
-    res = sexp_json_parse_exception(ctx, self, "unexpected character in json at", str, j);
+    res = sexp_json_read_exception(ctx, self, "unexpected character in json", in, sexp_make_character(ch));
     break;
   }
-  *i = j;
   return res;
 }
 
-sexp sexp_parse_json (sexp ctx, sexp self, sexp_sint_t n, sexp str) {
-  const char *s;
-  int i=0, len;
-  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
-  s = sexp_string_data(str);
-  len = sexp_string_size(str);
-  return parse_json(ctx, self, str, s, &i, len);
+sexp sexp_json_read (sexp ctx, sexp self, sexp_sint_t n, sexp in) {
+  sexp_assert_type(ctx, sexp_iportp, SEXP_IPORT, in);
+  return json_read(ctx, self, in);
 }
 
 
-
-
-sexp unparse_json (sexp ctx, sexp self, sexp obj);
-
-
-sexp unparse_json_fixnum(sexp ctx, sexp self, const sexp obj) {
-  sexp_gc_var2(res, tmp);
-  sexp_gc_preserve2(ctx, res, tmp);
-  res = SEXP_VOID;
-  int sign = 1;
-  long num = sexp_unbox_fixnum(obj);
-  char digit;
-  if (num == 0) {
-    res = sexp_c_string(ctx, "0", -1);
-  } else {
-    if (num < 0) {
-      sign = -1;
-      num = labs(num);
-    }
-    while (num > 0) {
-      digit = '0' + num%10;
-      num /= 10;
-
-      tmp = sexp_c_string(ctx, &digit, 1);
-      res = sexp_cons(ctx, tmp, res);
-    }
-    if (sign==-1) {
-      tmp = sexp_c_string(ctx, "-", -1);
-      res = sexp_cons(ctx, tmp, res);
-    }
-    res = sexp_string_concatenate(ctx, res, SEXP_FALSE);
-  }
-  sexp_gc_release2(ctx);
-  return res;
-}
-
+sexp json_write (sexp ctx, sexp self, sexp obj, sexp out);
 
 #define FLONUM_SIGNIFICANT_DIGITS 10
 #define FLONUM_EXP_MAX_DIGITS 3
-sexp unparse_json_flonum(sexp ctx, sexp self, const sexp obj) {
-  sexp_gc_var2(res, tmp);
-  sexp_gc_preserve2(ctx, res, tmp);
-  res = SEXP_VOID;
-  char cout[FLONUM_SIGNIFICANT_DIGITS + FLONUM_EXP_MAX_DIGITS + 5];
-    // Extra space for signs (x2), dot, E and \0
-
+sexp json_write_flonum(sexp ctx, sexp self, const sexp obj, sexp out) {
   if (sexp_infp(obj) || sexp_nanp(obj)) {
-    res = sexp_json_unparse_exception(ctx, self, "unable to encode number", obj);
-    sexp_gc_release2(ctx);
-    return res;
+    return sexp_json_write_exception(ctx, self, "unable to encode number", obj);
   }
-
+  /* Extra space for signs (x2), dot, E and \0 */
+  char cout[FLONUM_SIGNIFICANT_DIGITS + FLONUM_EXP_MAX_DIGITS + 5];
   snprintf(cout, sizeof(cout), "%.*G", FLONUM_SIGNIFICANT_DIGITS, sexp_flonum_value(obj));
-  res = sexp_c_string(ctx, cout, -1);
-  sexp_gc_release2(ctx);
-  return res;
+  sexp_write_string(ctx, cout, out);
+  return SEXP_VOID;
 }
 
 
-sexp unparse_json_string(sexp ctx, sexp self, const sexp obj) {
-  sexp_gc_var2(res, tmp);
-  sexp_gc_preserve2(ctx, res, tmp);
-  res = SEXP_VOID;
-
-  tmp = sexp_c_string(ctx, "\"", -1);
-  res = sexp_cons(ctx, tmp, res);
-
+sexp json_write_string(sexp ctx, sexp self, const sexp obj, sexp out) {
   char cout[32];  /* oversized to avoid snprintf warnings */
-  unsigned long ch, chh, chl;
+  sexp_sint_t ch, chh, chl;
+  sexp i, end = sexp_make_string_cursor(sexp_string_size(obj));
 
-  sexp_uint_t len = sexp_string_length(obj);
-  for(sexp_uint_t i=0; i!= len; i++) {
-    ch = sexp_unbox_character(sexp_string_ref(ctx, obj, sexp_make_fixnum(i)));
-    if(ch < 0x7F) {
-      switch(ch) {
+  sexp_write_char(ctx, '"', out);
+  for (i = sexp_make_string_cursor(0); i < end;
+       i = sexp_string_cursor_next(obj, i)) {
+    ch = sexp_unbox_character(sexp_string_cursor_ref(ctx, obj, i));
+    if (ch < 0x7F) {
+      switch (ch) {
         case '\\':
-          snprintf(cout, sizeof(cout), "\\\\");
-          break;
-        case '/':
-          snprintf(cout, sizeof(cout), "\\/");
+          sexp_write_string(ctx, "\\\\", out);
           break;
         case '\b':
-          snprintf(cout, sizeof(cout), "\\b");
+          sexp_write_string(ctx, "\\b", out);
           break;
         case '\f':
-          snprintf(cout, sizeof(cout), "\\f");
+          sexp_write_string(ctx, "\\f", out);
           break;
         case '\n':
-          snprintf(cout, sizeof(cout), "\\n");
+          sexp_write_string(ctx, "\\n", out);
           break;
         case '\r':
-          snprintf(cout, sizeof(cout), "\\r");
+          sexp_write_string(ctx, "\\r", out);
           break;
         case '\t':
-          snprintf(cout, sizeof(cout), "\\t");
+          sexp_write_string(ctx, "\\t", out);
           break;
         default:
-          snprintf(cout, sizeof(cout), "%c", (int)ch);
+          sexp_write_char(ctx, ch, out);
           break;
       }
-    } else if(ch <= 0xFFFF) {
+    } else if (ch <= 0xFFFF) {
       snprintf(cout, sizeof(cout), "\\u%04lX", ch);
+      sexp_write_string(ctx, cout, out);
     } else {
       // Surrogate pair
       chh = (0xD800 - (0x10000 >> 10) + ((ch) >> 10));
       chl = (0xDC00 + ((ch) & 0x3FF));
       if (chh > 0xFFFF || chl > 0xFFFF) {
-        res = sexp_json_unparse_exception(ctx, self, "unable to encode string", obj);
-        sexp_gc_release2(ctx);
-        return res;
+        return sexp_json_write_exception(ctx, self, "unable to encode string", obj);
       }
       snprintf(cout, sizeof(cout), "\\u%04lX\\u%04lX", chh, chl);
+      sexp_write_string(ctx, cout, out);
     }
-    tmp = sexp_c_string(ctx, cout, -1);
-    res = sexp_cons(ctx, tmp, res);
   }
+  sexp_write_char(ctx, '"', out);
 
-  tmp = sexp_c_string(ctx, "\"", -1);
-  res = sexp_cons(ctx, tmp, res);
-
-  res = sexp_nreverse(ctx, res);
-  res = sexp_string_concatenate(ctx, res, SEXP_FALSE);
-
-  sexp_gc_release2(ctx);
-  return res;
+  return SEXP_VOID;
 }
 
-sexp unparse_json_array(sexp ctx, sexp self, const sexp obj) {
-  sexp_gc_var2(res, tmp);
-  sexp_gc_preserve2(ctx, res, tmp);
-  res = SEXP_VOID;
-
-  tmp = sexp_c_string(ctx, "[", -1);
-  res = sexp_cons(ctx, tmp, res);
-
-  int len = sexp_vector_length(obj);
-  for (int i=0; i!=len; i++) {
-    tmp = unparse_json(ctx, self, sexp_vector_ref(obj, sexp_make_fixnum(i)));
+sexp json_write_array(sexp ctx, sexp self, const sexp obj, sexp out) {
+  sexp tmp;
+  int len = sexp_vector_length(obj), i;
+  sexp_write_string(ctx, "[", out);
+  for (i = 0; i < len; ++i) {
+    tmp = json_write(ctx, self, sexp_vector_ref(obj, sexp_make_fixnum(i)), out);
     if (sexp_exceptionp(tmp)) {
-      sexp_gc_release2(ctx);
       return tmp;
     }
-    res = sexp_cons(ctx, tmp, res);
-
-    if (i != len-1) {
-      tmp = sexp_c_string(ctx, ",", -1);
-      res = sexp_cons(ctx, tmp, res);
+    if (i < len - 1) {
+      sexp_write_char(ctx, ',', out);
     }
   }
-
-  tmp = sexp_c_string(ctx, "]", -1);
-  res = sexp_cons(ctx, tmp, res);
-
-  res = sexp_nreverse(ctx, res);
-  res = sexp_string_concatenate(ctx, res, SEXP_FALSE);
-
-  sexp_gc_release2(ctx);
-  return res;
+  sexp_write_string(ctx, "]", out);
+  return SEXP_VOID;
 }
 
-
-sexp unparse_json_object(sexp ctx, sexp self, const sexp obj) {
-  sexp_gc_var6(res, tmp, it, cur, key, val);
-  sexp_gc_preserve6(ctx, res, tmp, it, cur, key, val);
-  res = SEXP_VOID;
-
-  tmp = sexp_c_string(ctx, "{", -1);
-  res = sexp_cons(ctx, tmp, res);
-
-  int len = sexp_unbox_fixnum(sexp_length(ctx, obj));
-  it = obj;
-  for (int i=0; i!=len; i++) {
-    cur = sexp_car(it);
-    if (!sexp_pairp(cur)) {
-      res = sexp_json_unparse_exception(ctx, self, "unable to encode key-value pair: not a pair", obj);
-      goto except;
-    }
-
-    // Key
+sexp json_write_object(sexp ctx, sexp self, const sexp obj, sexp out) {
+  sexp ls, cur, key, val, tmp;
+  if (sexp_length(ctx, obj) == SEXP_FALSE)
+    return sexp_json_write_exception(ctx, self, "unable to encode circular list", obj);
+  sexp_write_char(ctx, '{', out);
+  for (ls = obj; sexp_pairp(ls); ls = sexp_cdr(ls)) {
+    if (ls != obj)
+      sexp_write_char(ctx, ',', out);
+    cur = sexp_car(ls);
+    if (!sexp_pairp(cur))
+      return sexp_json_write_exception(ctx, self, "unable to encode key-value pair: not a pair", obj);
     key = sexp_car(cur);
-    if (!(sexp_symbolp(key) /*|| sexp_stringp(key)*/)) {
-      res = sexp_json_unparse_exception(ctx, self, "unable to encode key: not a symbol", key);
-      goto except;
-    }
-    tmp = unparse_json(ctx, self, key);
-    if (sexp_exceptionp(tmp)) {
-      res = tmp;
-      goto except;
-    }
-    res = sexp_cons(ctx, tmp, res);
-
-    // Separator
-    tmp = sexp_c_string(ctx, ":", -1);
-    res = sexp_cons(ctx, tmp, res);
-
-    // Value
+    if (!sexp_symbolp(key))
+      return sexp_json_write_exception(ctx, self, "unable to encode key: not a symbol", key);
+    tmp = json_write(ctx, self, key, out);
+    if (sexp_exceptionp(tmp))
+      return tmp;
+    sexp_write_char(ctx, ':', out);
     val = sexp_cdr(cur);
-    tmp = unparse_json(ctx, self, val);
-    res = sexp_cons(ctx, tmp, res);
-
-    if (i != len-1) {
-      tmp = sexp_c_string(ctx, ",", -1);
-      res = sexp_cons(ctx, tmp, res);
-    }
-    it = sexp_cdr(it);
+    tmp = json_write(ctx, self, val, out);
+    if (sexp_exceptionp(tmp))
+      return tmp;
   }
-
-  tmp = sexp_c_string(ctx, "}", -1);
-  res = sexp_cons(ctx, tmp, res);
-
-  res = sexp_nreverse(ctx, res);
-  res = sexp_string_concatenate(ctx, res, SEXP_FALSE);
-except:
-  sexp_gc_release6(ctx);
-  return res;
+  sexp_write_char(ctx, '}', out);
+  return SEXP_VOID;
 }
 
-sexp unparse_json (sexp ctx, sexp self, sexp obj) {
+sexp json_write (sexp ctx, sexp self, const sexp obj, sexp out) {
   sexp_gc_var1(res);
   sexp_gc_preserve1(ctx, res);
   res = SEXP_VOID;
-
-  if( sexp_symbolp(obj) ) {
-    obj = sexp_symbol_to_string(ctx, obj);
-    res = unparse_json_string(ctx, self, obj);
+  if (sexp_symbolp(obj)) {
+    res = sexp_symbol_to_string(ctx, obj);
+    res = json_write_string(ctx, self, res, out);
   } else if (sexp_stringp(obj)) {
-    res = unparse_json_string(ctx, self, obj);
+    res = json_write_string(ctx, self, obj, out);
   } else if (sexp_listp(ctx, obj) == SEXP_TRUE) {
-    res = unparse_json_object(ctx, self, obj);
+    res = json_write_object(ctx, self, obj, out);
   } else if (sexp_vectorp(obj)) {
-    res = unparse_json_array(ctx, self, obj);
-  } else if(sexp_fixnump(obj)) {
-    res = unparse_json_fixnum(ctx, self, obj);
+    res = json_write_array(ctx, self, obj, out);
+  } else if (sexp_fixnump(obj)) {
+    res = sexp_write(ctx, obj, out);
   } else if (sexp_flonump(obj)) {
-    res = unparse_json_flonum(ctx, self, obj); // OTHER TYPES? bignum etc?
+    res = json_write_flonum(ctx, self, obj, out);
+#if SEXP_USE_BIGNUMS
+  } else if (sexp_bignump(obj)) {
+    res = sexp_make_flonum(ctx, sexp_bignum_to_double(obj));
+    res = json_write_flonum(ctx, self, res, out);
+#endif
   } else if (obj == SEXP_FALSE) {
-    res = sexp_c_string(ctx, "false", -1);
+    sexp_write_string(ctx, "false", out);
   } else if (obj == SEXP_TRUE) {
-    res = sexp_c_string(ctx, "true", -1);
+    sexp_write_string(ctx, "true", out);
   } else if (obj == SEXP_NULL) {
-    res = sexp_c_string(ctx, "null", -1);
+    sexp_write_string(ctx, "null", out);
   } else if (sexp_pairp(obj)) {
-    res = sexp_json_unparse_exception(ctx, self, "unable to encode elemente: key-value pair out of object", obj);
+    res = sexp_json_write_exception(ctx, self, "unable to encode elemente: key-value pair out of object", obj);
   } else {
-    res = sexp_json_unparse_exception(ctx, self, "unable to encode element", obj);
+    res = sexp_json_write_exception(ctx, self, "unable to encode element", obj);
   }
   sexp_gc_release1(ctx);
   return res;
 }
 
-sexp sexp_unparse_json (sexp ctx, sexp self, sexp_sint_t n, sexp obj) {
-  return unparse_json(ctx, self, obj);
+sexp sexp_json_write (sexp ctx, sexp self, sexp_sint_t n, sexp obj, sexp out) {
+  sexp_assert_type(ctx, sexp_oportp, SEXP_OPORT, out);
+  return json_write(ctx, self, obj, out);
 }
 
 
@@ -577,7 +479,7 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
   if (!(sexp_version_compatible(ctx, version, sexp_version)
         && sexp_abi_compatible(ctx, abi, SEXP_ABI_IDENTIFIER)))
     return SEXP_ABI_ERROR;
-  sexp_define_foreign(ctx, env, "parse-json", 1, sexp_parse_json);
-  sexp_define_foreign(ctx, env, "unparse-json", 1, sexp_unparse_json);
+  sexp_define_foreign(ctx, env, "json-read", 1, sexp_json_read);
+  sexp_define_foreign(ctx, env, "json-write", 2, sexp_json_write);
   return SEXP_VOID;
 }
diff --git a/lib/chibi/json.sld b/lib/chibi/json.sld
index 51013978..e378ad94 100644
--- a/lib/chibi/json.sld
+++ b/lib/chibi/json.sld
@@ -1,6 +1,15 @@
 
 (define-library (chibi json)
   (import (scheme base))
-  (export parse-json)
-  (export unparse-json)
-  (include-shared "json"))
+  (export string->json json->string json-read json-write)
+  (include-shared "json")
+  (begin
+    (define (string->json str)
+      (let* ((in (open-input-string str))
+             (res (json-read in)))
+        (close-input-port in)
+        res))
+    (define (json->string json)
+      (let ((out (open-output-string)))
+        (json-write json out)
+        (get-output-string out)))))