ps/step1_read_print.ps

   1 /runlibfile where { pop }{ /runlibfile { run } def } ifelse %
   2 (types.ps) runlibfile
   3 (reader.ps) runlibfile
   4 (printer.ps) runlibfile
   5
   6 % read
   7 /_readline { print flush (%stdin) (r) file 1024 string readline } def
   8
   9 /READ {
  10     /str exch def
  11     str read_str
  12 } def
  13
  14
  15 % eval
  16 /EVAL { 2 dict begin
  17     % just "return" the "ast"
  18     /env exch def
  19     /ast exch def
  20     ast
  21 end } def
  22
  23
  24 % print
  25 /PRINT {
  26     true _pr_str
  27 } def
  28
  29
  30 % repl
  31 /REP { READ (stub env) EVAL PRINT } def
  32
  33 % repl loop
  34 { %loop
  35     (user> ) _readline
  36     not { exit } if  % exit if EOF
  37
  38     { %try
  39         REP print (\n) print
  40     } stopped {
  41         (Error: ) print
  42         get_error_data false _pr_str print (\n) print
  43         $error /newerror false put
  44         $error /errorinfo null put
  45         clear
  46         cleardictstack
  47     } if
  48 } bind loop
  49
  50 (\n) print  % final newline before exit for cleanliness
  51 quit