lis.ps

%!
(util.ps) run
(lambda.ps) run
(eval.ps) run

/pdict_states <<
  (lambda) { /pdict pdict_lambda def mark }
  (quote)  { /pdict pdict_quote def }
>> def

/pdict_default <<
  40 { count 0 eq { mark } { isMark not { mark } if } ifelse mark } % '('
  41 { isMark { pop } { genStr transit } ifelse eval mark } % ')'
  32 { isMark not { genStr transit mark } if } % ' '
>> def

/pdict_lambda <<
  40 {  } % '(' do not delete
  41 { isMark { pop } { genStr } ifelse ] mark /pdict pdict_default def } % ')'
  32 { isMark not { genStr mark } if } % ' '
>> def

/open_brackets 1 def

/pdict_quote <<
  40 { /open_brackets open_brackets 1 add def 40 } % '('
  41 { % ')'
        /open_brackets open_brackets 1 sub def
        open_brackets 0 eq
        {
          /open_brackets open_brackets 1 add def
          genStr eval mark
          /pdict pdict_default def
        }
        { 41 } ifelse
     }
>> def

/pdict pdict_default def

/transit {
  dup pdict_states exch known
  {
    dup pdict_states exch get exec
  } if
} def

/parse {
  dup 0 get 40 ne % if the stmnt starts with no brackets
  { getVal } 
  {
    {
      dup pdict exch known
      { pdict exch get exec }
      if
    } forall

    open_brackets 1 eq
    { pop exec } % clear_par_arr is here just for testing
    { (Some brackets have not been closed\n) print }
    ifelse
  } ifelse
} def

/lisps
{
   (Lisp Interpreter by Alex and Gabriel\n)
   print
   {
   (lis.ps >) print flush
      readLineStdin % - string bool
      not
      { pop exit }
      if

      dup () ne % if no empty stmnt
      { parse }
      if
      dup () ne % if not None
      { pstack } % print stack
      if
      clear % clear stack
   } loop
   clearvars
} def