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Newsgroups: comp.lang.postscript
Subject: JSON reader/writer in PostScript
Date: Wed, 04 Sep 2019 01:19:41 +0000
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I wrote a program in PostScript for reading/writing JSON data. You can use
the following functions:

* JSON.read ( file -- object ) Read JSON data from the file. An object will
become a dictionary, with names (rather than strings) as keys. See also
JSON.utf8 below.

* JSON.write ( file object -- ) Write JSON data to the file. The object
must be a null, boolean, string, name, integer, real, array, or dictionary.
The JSON.utf8 option is unused; characters outside of the ASCII range are
always written exactly as in the string. (ASCII control characters, and any
character not allowed unescaped, will be escaped, though.)

* JSON.utf8 - You can redefine this (like "/JSON.utf8 true def"); it is
set to false by default. If false, only the low 8-bits of any character
code specified by \u escapes are used. If true, then \u escapes will be
converted into UTF-8. Bytes that are not escaped will just be passed
through as is, regardless of this setting.

Currently, the JSON.utf8 option is not implemented, so it must always be
false, and it will not work if true. If I fix that later, then I will post
a follow-up with the corrected program.

You can also write a follow-up message if you have a comment of it, please.

The below (between "===BEGIN CODE===" and "===END CODE===") is the
PostScript program.

===BEGIN CODE===
% JSON implementation in PostScript
% (public domain)

currentpacking true setpacking
/JSON.utf8 false def
/.JSON.file null def
/.JSON.str 65535 string def
/.JSON.hex (16#????) def
/.JSON.backchar 0 def
/.JSON.char 0 def

/.JSON.namech 256 string def
.JSON.namech 43 1 put %+
JSON.namech 45 1 put %-
.JSON.namech 46 1 put %.
8 1 57 {.JSON.namech exch 1 put} for %0-9
.JSON.namech 69 1 put %E
7 1 122 {.JSON.namech exch 1 put} for %a-z

/.JSON.escape 256 string def
0 1 255 {.JSON.escape exch dup put} for
.JSON.escape 98 8 put
JSON.escape 102 12 put
.JSON.escape 110 10 put
JSON.escape 114 13 put
.JSON.escape 116 9 put
JSON.escape 117 0 put

/.JSON.readnum {
  .JSON.str 0 .JSON.char put
  1
  {.JSON.file read {
    .JSON.namech 1 index get 0 eq {
      /.JSON.backchar exch store
      .JSON.str exch 0 exch getinterval cvr
      exit
    } {
      .JSON.str exch 2 index exch put
      1 add
    } ifelse
  } {JSON.badinput} ifelse} loop
} bind def

/.JSON.readword {
  {.JSON.file read {
    .JSON.namech 1 index get 0 eq {
      /.JSON.backchar exch store
      exit
    } {pop} ifelse
  } {JSON.badinput} ifelse} loop
} bind def

/.JSON.readstring {
  0 {
    .JSON.file read pop
    dup 34 eq {
      % End of string
      pop dup string dup 2 index
      .JSON.str exch 0 exch getinterval
      0 exch putinterval exch pop
      exit
    } {
      % Character
      .JSON.str 2 index 2 index put
      92 eq {
        .JSON.str 1 index .JSON.escape .JSON.file read pop get put
        .JSON.str 1 index get 0 eq {
          .JSON.file .JSON.hex 3 4 getinterval readstring pop pop
          /.JSON.char .JSON.hex cvi store
          .JSON.char 127 gt JSON.utf8 and {
            % Not yet implemented
          } {
            .JSON.str 1 index .JSON.char 255 and put
          } ifelse
        } if
      } if
      1 add
    } ifelse
  } loop
} bind def

/.JSON.parsech 256 array def
33 1 255 {.JSON.parsech exch /JSON.badinput cvx put} for
0 1 32 {.JSON.parsech exch null cvx put} for %spaces
.JSON.parsech 34 /.JSON.readstring load put %"
JSON.parsech 43 /.JSON.readnum load put %+
.JSON.parsech 44 null cvx put %,
JSON.parsech 45 /.JSON.readnum load put %-
48 1 57 {.JSON.parsech exch /.JSON.readnum load put} for %numbers
.JSON.parsech 58 /cvn load put %:
JSON.parsech 91 mark put %[
.JSON.parsech 93 (]) cvn load put %]
JSON.parsech 102 {false .JSON.readword} put %f
.JSON.parsech 110 {null .JSON.readword} put %n
JSON.parsech 116 {true .JSON.readword} put %t
.JSON.parsech 123 mark put %{
JSON.parsech 125 (>>) cvn load put %}

/.JSON.parse {  % ( -- object )
  .JSON.backchar 0 eq {
    .JSON.file read
  } {
    .JSON.backchar /.JSON.backchar 0 store true
  } ifelse {
    /.JSON.char exch store
    .JSON.parsech .JSON.char get exec
    .JSON.parse
  } if
} bind def

/.JSON.charx [32 {true} repeat 224 {false} repeat] def
.JSON.charx 34 true put
JSON.charx 92 true put
/.JSON.writechar {
  .JSON.charx 1 index get {
    .JSON.file (\\u00) writestring
    dup 16 lt {.JSON.file 48 write} if
    16 .JSON.str cvrs .JSON.file exch writestring
  } {
    .JSON.file exch write
  } ifelse
} def

/.JSON.writedict <<
  /arraytype {.JSON.file 91 write false exch {exch {.JSON.file 44 write} if .JSON.write true} forall pop .JSON.file 93 write}
  /booleantype {.JSON.str cvs .JSON.file exch writestring}
  /dicttype {.JSON.file 123 write false exch {3 -1 roll {.JSON.file 44 write} if exch .JSON.write .JSON.file 58 write .JSON.write true} forall pop .JSON.file 125 write}
  /integertype {.JSON.str cvs .JSON.file exch writestring}
  /nametype {.JSON.str cvs .JSON.write}
  /nulltype {.JSON.file (null) writestring}
  /realtype {.JSON.str cvs .JSON.file exch writestring}
  /stringtype {.JSON.file 34 write {.JSON.writechar} forall .JSON.file 34 write}
>> def

/JSON.read {/.JSON.file exch store .JSON.parse} bind def
/.JSON.write {dup type .JSON.writedict exch get exec} bind def
/JSON.write {exch /.JSON.file exch store .JSON.write .JSON.file 10 write} bind def

setpacking
===END CODE===


-- 
Note: I am not always able to read/post messages during Monday-Friday.