ps/step1_read_print.ps

   1 (types.ps) run
   2 (reader.ps) run
   3 (printer.ps) run
   4
   5 % read
   6 /_readline { print flush (%stdin) (r) file 99 string readline } def
   7
   8 /READ {
   9     /str exch def
  10     str read_str
  11 } def
  12
  13
  14 % eval
  15 /EVAL { 2 dict begin
  16     % just "return" the "ast"
  17     /env exch def
  18     /ast exch def
  19     ast
  20 end } def
  21
  22
  23 % print
  24 /PRINT {
  25     true _pr_str
  26 } def
  27
  28
  29 % repl
  30 /REP { READ (stub env) EVAL PRINT } def
  31
  32 % repl loop
  33 { %loop
  34     (user> ) _readline
  35     not { exit } if  % exit if EOF
  36
  37     { %try
  38         REP print (\n) print
  39     } stopped {
  40         (Error: ) print
  41         get_error_data false _pr_str print (\n) print
  42         $error /newerror false put
  43         $error /errorinfo null put
  44         clear
  45         cleardictstack
  46     } if
  47 } bind loop
  48
  49 (\n) print  % final newline before exit for cleanliness
  50 quit