ps/step0_repl.ps

   1 % read
   2 /READ {
   3     % just "return" the input string
   4     /str exch def
   5     str
   6 } def
   7
   8
   9 % eval
  10 /EVAL {
  11     % just "return" the "ast"
  12     /env exch def
  13     /ast exch def
  14     ast
  15 } def
  16
  17
  18 % print
  19 /PRINT {
  20     % just "return" the expression
  21     /exp exch def
  22     exp
  23 } def
  24
  25
  26 % repl
  27 /REP {
  28     READ (stub env) EVAL PRINT
  29 } def
  30
  31 /stdin (%stdin) (r) file def
  32
  33 { % loop
  34     (user> ) print flush
  35
  36     %(%lineedit) (r) file 99 string readline
  37     stdin 99 string readline
  38
  39     not { exit } if  % exit if EOF
  40
  41     %(\ngot line: ) print dup print (\n) print flush
  42     REP print (\n) print
  43 } bind loop
  44
  45 (\n) print  % final newline before exit for cleanliness
  46 quit