--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/json.ur	Thu Dec 02 11:10:57 2010 -0500
@@ -0,0 +1,192 @@
+class json a = {ToJson : a -> string,
+                FromJson : string -> a * string}
+
+fun mkJson [a] (x : {ToJson : a -> string,
+                     FromJson : string -> a * string}) = x
+
+fun skipSpaces s =
+    let
+        val len = String.length s
+
+        fun skip i =
+            if i >= len then
+                ""
+            else
+                let
+                    val ch = String.sub s i
+                in
+                    if Char.isSpace ch then
+                        skip (i+1)
+                    else
+                        String.substring s {Start = i, Len = len-i}
+                end
+    in
+        skip 0
+    end
+
+fun toJson [a] (j : json a) : a -> string = j.ToJson
+
+fun fromJson [a] (j : json a) (s : string) : a =
+    let
+        val (v, s') = j.FromJson (skipSpaces s)
+    in
+        if String.all Char.isSpace s' then
+            v
+        else
+            error <xml>Extra content at end of JSON record: {[s']}</xml>
+    end
+
+fun escape s =
+    let
+        val len = String.length s
+
+        fun esc i =
+            if i >= len then
+                "\""
+            else
+                let
+                    val ch = String.sub s i
+                in
+                    (if ch = #"\"" || ch = #"\\" then
+                         "\\" ^ String.str ch
+                     else
+                         String.str ch) ^ esc (i+1)
+                end
+    in
+        "\"" ^ esc 0
+    end
+
+fun unescape s =
+    let
+        val len = String.length s
+
+        fun findEnd i =
+            if i >= len then
+                error <xml>JSON unescape: string ends before quote: {[s]}</xml>
+            else
+                let
+                    val ch = String.sub s i
+                in
+                    case ch of
+                        #"\"" => i
+                      | #"\\" =>
+                        if i+1 >= len then
+                            error <xml>JSON unescape: Bad escape sequence: {[s]}</xml>
+                        else
+                            findEnd (i+2)
+                      | _ => findEnd (i+1)
+                end
+
+        val last = findEnd 1
+
+        fun unesc i =
+            if i >= last then
+                ""
+            else
+                let
+                    val ch = String.sub s i
+                in
+                    case ch of
+                        #"\\" =>
+                        if i+1 >= len then
+                            error <xml>JSON unescape: Bad escape sequence: {[s]}</xml>
+                        else
+                            String.str (String.sub s (i+1)) ^ unesc (i+2)
+                      | _ => String.str ch ^ unesc (i+1)
+                end
+    in
+        if len = 0 || String.sub s 0 <> #"\"" then
+            error <xml>JSON unescape: String doesn't start with double quote: {[s]}</xml>
+        else
+            (unesc 1, String.substring s {Start = last+1, Len = len-last-1})
+    end
+
+val json_string = {ToJson = escape,
+                   FromJson = unescape}
+
+fun numIn [a] (_ : read a) s : a * string =
+    let
+        val len = String.length s
+
+        fun findEnd i =
+            if i >= len then
+                i
+            else
+                let
+                    val ch = String.sub s i
+                in
+                    if Char.isDigit ch || ch = #"-" || ch = #"." || ch = #"E" || ch = #"e" then
+                        findEnd (i+1)
+                    else
+                        i
+                end
+
+        val last = findEnd 0
+    in
+        (readError (String.substring s {Start = 0, Len = last}), String.substring s {Start = last, Len = len-last})
+    end
+
+fun json_num [a] (_ : show a) (_ : read a) : json a = {ToJson = show,
+                                                       FromJson = numIn}
+
+val json_int = json_num
+val json_float = json_num
+
+val json_bool = {ToJson = fn b => if b then "true" else "false",
+                 FromJson = fn s => if String.isPrefix {Full = s, Prefix = "true"} then
+                                        (True, String.substring s {Start = 4, Len = String.length s - 4})
+                                    else if String.isPrefix {Full = s, Prefix = "false"} then
+                                        (False, String.substring s {Start = 5, Len = String.length s - 5})
+                                    else
+                                        error <xml>JSON: bad boolean string: {[s]}</xml>}
+
+fun json_list [a] (j : json a) : json (list a) =
+    let
+        fun toJ' (ls : list a) : string =
+            case ls of
+                [] => ""
+              | x :: ls => "," ^ toJson j x ^ toJ' ls
+
+        fun toJ (x : list a) : string =
+            case x of
+                [] => "[]"
+              | x :: [] => "[" ^ toJson j x ^ "]"
+              | x :: ls => "[" ^ toJson j x ^ toJ' ls ^ "]"
+
+        fun fromJ (s : string) : list a * string =
+            let
+                fun fromJ' (s : string) : list a * string =
+                    if String.length s = 0 then
+                        error <xml>JSON list doesn't end with ']'</xml>
+                    else
+                        let
+                            val ch = String.sub s 0
+                        in
+                            case ch of
+                                #"]" => ([], String.substring s {Start = 1, Len = String.length s - 1})
+                              | _ =>
+                                let
+                                    val (x, s') = j.FromJson s
+                                    val s' = skipSpaces s'
+                                    val s' = if String.length s' = 0 then
+                                                 error <xml>JSON list doesn't end with ']'</xml>
+                                             else if String.sub s' 0 = #"," then
+                                                 skipSpaces (String.substring s' {Start = 1, Len = String.length s' - 1})
+                                             else
+                                                 s'
+
+                                    val (ls, s'') = fromJ' s'
+                                in
+                                    (x :: ls, s'')
+                                end
+                        end
+            in
+                if String.length s = 0 || String.sub s 0 <> #"[" then
+                    error <xml>JSON list doesn't start with '[': {[s]}</xml>
+                else
+                    fromJ' (skipSpaces (String.substring s {Start = 1, Len = String.length s - 1}))
+            end
+    in
+        {ToJson = toJ,
+         FromJson = fromJ}
+    end