#* 
  this script just parses/checks crockfords json number format, eg:
    -0, 0, -123.333, 123, 100, 0.123, -0.200, 0.00
    -1.44e55, 0.1E0123, 8e012, 1E+02, 2E-123

NOTES

  The grammar used in this script has no relation to the
  grammar shown at www.json.org. This is often the case for
  pep scripts. The grammar needs to be designed to suit the
  machine. This entire script just parses the following
  regular expression:

    >> [-]?(0|[1-9][0-9]*)(\.[0-9]+)([eE][-+][0-9]+)

  As can be seen the regular expression is far more succinct
  and easier to read, so the question may be... "why on earth
  would we use a pep script to do this, instead of a regex??". 

  The answer may be as follows: The pep script may be faster
  (I will be interested to check this) and pep script can give
  error messages with a line/character number about what is
  wrong with the number.

  Whitespace is completely ignored in this script.

TESTING
  
  * test this script
  >> pep -f eg/json.number.pss -i ' -0.123e+0123 '
   
HISTORY
 
  18 july 2020

    correcting some errors in the script. Also, may
    produce output in the form -0.1 x (10^33)

  11 july 2020

     rewrote script completely. based on parsing integers with "while [0-9]"
     Appears to be working well. should be simplifiable.

  9 july 2020
     script begun. There are some tricky elements to it, 
     considering 0-9 and 1-9. what is an integer fraction exponent.
     need to choose token types carefully

*#

 begin {
   add "
   Checking number is in json scientific format 
   (eg -123.456E+0012) See www.json.org for the 
   number grammar 
   \n";
   print; clear;
 }

# -------
# lexing phase of the script- create parse tokens

  read;
  [:space:] { clear; }
  [+-.] { put; add '*'; push; .reparse }
  [0-9] { while [0-9]; put; clear; add "int*"; push; .reparse }
  'e','E' { 
    clear; add "*(10^"; put; 
    clear; add "e*"; push; .reparse 
  }

# --------
# parsing phase

parse>

  #---------
  # 2 tokens
  pop; pop;

  #---------
  # some errors 

  E".*".!".*" {
    !B"int*".!B"-int*" {
      clear; add "Misplaced decimal point in '.' at char "; chars; add "\n";
      print; quit;
    }
  }

  E"+*".!"+*" {
    !B"e*" {
      clear; add "Misplaced '+' at char "; chars; add "\n";
      print; quit;
    }
  }

  E"e*".!"e*" {
    !B"decimal*".!B"int*".!B"-int*" {
      clear; add "Misplaced 'e' at char "; chars; add "\n";
      print; quit;
    }
  }

  #---------
  # reductions

  ".*int*" {
    clear; get; ++; get; --; put; clear;
    add "fraction*"; push; .reparse
  }

  "+*int*" {
    clear; 
    # the plus symbol + should be redundant here
    ++; get; --; put; clear;
    add "+int*"; push; .reparse
  }

  "-*int*" {
    clear; get; ++; get; --; put; clear;
    add "-int*"; push; .reparse
  }

  "+int*fraction*" {
    clear;
    add "json numbers cannot have a '+' prefix \n";
    print; quit;
  }

  "int*fraction*","-int*fraction*" {
    clear; get; 
    B"-" { clop; }
    !B"0","0" {
      clear; get; ++; get; --; put; clear;
      add "decimal*"; push; .reparse
    }
    clear;
    add "Multi-digit json numbers must begin with 1-9 ("; get; add ") \n";
    print; quit;
  }

  "int*exponent*","-int*exponent*" {
    clear; get; 
    B"-" { clop; }
    !B"0","0" {
      clear; get; ++; get; --; put; clear;
      add "number*"; push; .reparse
    }
    clear;
    add "Multi-digit json numbers must begin with 1-9 ("; get; add ") \n";
    print; quit;
  }

  "e*int*","e*-int*","e*+int*" {
    clear; get; ++; get; --; add ")"; put; clear;
    add "exponent*"; push; .reparse
  }

  "decimal*exponent*" {
    clear; get; ++; get; --; put; clear;
    add "number*"; push; .reparse
  }

  push; push;

  (eof) {
    pop; pop;

    "int*" {
      clear; get; 
      B"0".!"0" {
        clear; 
        add "json multidigit numbers must start with '1': "; 
        get; add "\n"; print; quit;
      }
      clear; add "int*";
    }

    "-int*" {
      clear; get; B"-" { clop; }
      B"0".!"0" {
        clear; 
        add "json multidigit numbers must start with '1': "; 
        get; add "\n"; print; quit;
      }
      clear; add "-int*";
    }

    "+int*" {
      clear; 
      add "json numbers cannot have a '+' prefix "; 
      get; add "\n"; print; quit;
    }

    "number*","decimal*","-int*","int*" {
      clear; 
      add "Valid json scientific number: "; get; add "\n"; 
      print; quit;
    }
    push; push;
    add "Invalid json number \nParse stack was: "; print; clear;
    unstack; replace "*" " "; add "\n"; print; clear; quit;
  }