Began working on json library (fresh start after thinking about instantiation in...

diff --git a/src/lib/json.pl b/src/lib/json.pl
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+++ b/src/lib/json.pl
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+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written Apr 2021 by Aram Panasenco ([email protected])
+   Part of Scryer Prolog.
+   
+   BSD 3-Clause License
+   
+   Copyright (c) 2021, Aram Panasenco
+   All rights reserved.
+   
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions are met:
+   
+   * Redistributions of source code must retain the above copyright notice, this
+     list of conditions and the following disclaimer.
+   
+   * Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+   
+   * Neither the name of the copyright holder nor the names of its
+     contributors may be used to endorse or promote products derived from
+     this software without specific prior written permission.
+   
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+   AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+   DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+   FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+   SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+   CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+   OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(json, [
+                 json_whitespace//0,
+                 json_string//1
+                ]).
+
+:- use_module(library(charsio)).
+:- use_module(library(clpz)).
+:- use_module(library(dcgs)).
+:- use_module(library(dif)).
+:- use_module(library(error)).
+:- use_module(library(lists)).
+
+char_uniontypes(Char, Types) :-
+    must_be(list, Types),
+    bagof(Type, (char_type(Char, Type), member(Type, Types)), [_|_]).
+
+json_whitespace --> "".
+json_whitespace --> " ", json_whitespace.
+json_whitespace --> "\n", json_whitespace.
+json_whitespace --> "\r", json_whitespace.
+json_whitespace --> "\t", json_whitespace.
+
+escape_map([
+    '"' - '"',
+    ('\\') - ('\\'),
+    ('/') - ('/'),
+    '\b' - 'b',
+    '\f' - 'f',
+    '\n' - 'n',
+    '\r' - 'r',
+    '\t' - 't'
+]).
+
+hex(0) --> "0".
+hex(1) --> "1".
+hex(2) --> "2".
+hex(3) --> "3".
+hex(4) --> "4".
+hex(5) --> "5".
+hex(6) --> "6".
+hex(7) --> "7".
+hex(8) --> "8".
+hex(9) --> "9".
+hex(10) --> "a".
+hex(11) --> "b".
+hex(12) --> "c".
+hex(13) --> "d".
+hex(14) --> "e".
+hex(15) --> "f".
+
+inner_string("") --> "".
+inner_string([PrintChar | Tail]) -->
+    [PrintChar],
+    {
+        escape_map(EscapeMap),
+        \+ member(PrintChar-_, EscapeMap),
+        (
+            PrintChar = ' '
+            ; char_uniontypes(PrintChar, [alphanumeric, ascii_graphic])
+        )
+    },
+    inner_string(Tail).
+inner_string([EscapeChar | Tail]) -->
+    "\\",
+    [PrintChar],
+    {
+        escape_map(EscapeMap),
+        member(EscapeChar-PrintChar, EscapeMap)
+    },
+    inner_string(Tail).
+inner_string([NonPrintChar | Tail]) -->
+    "\\u",
+    {
+        [H1, H2, H3, H4] ins 0..15,
+        NonPrintCharCode in 0..65535,
+        NonPrintCharCode #= H1 * 16^3 + H2 * 16^2 + H3 * 16 + H4,
+        (
+            ground(NonPrintChar) ->
+            escape_map(EscapeMap),
+            \+ member(NonPrintChar-_, EscapeMap),
+            dif(NonPrintChar, ' '),
+            \+ char_uniontypes(NonPrintChar, [alphanumeric, ascii_graphic]),
+            char_code(NonPrintChar, NonPrintCharCode)
+            ; true
+        )
+    },
+    hex(H1),
+    hex(H2),
+    hex(H3),
+    hex(H4),
+    {
+        \+ ground(NonPrintChar) ->
+        char_code(NonPrintChar, NonPrintCharCode)
+        ; true
+    },
+    inner_string(Tail).
+
+json_string(Inner) --> "\"", inner_string(Inner), "\"".