ps/step2_eval.ps

   1 (types.ps) run
   2 (reader.ps) run
   3
   4 % read
   5 /READ {
   6     /str exch def
   7     str read_str
   8 } def
   9
  10
  11 % eval
  12 /eval_ast { 2 dict begin
  13     /env exch def
  14     /ast exch def
  15     %(eval_ast: ) print ast ==
  16     /nametype ast type eq { %if symbol
  17         env ast known {
  18             env ast get
  19         }{
  20             (') ast pr_str (' not found)
  21             concatenate concatenate throw
  22         } ifelse
  23     }{ /arraytype ast type eq { %elseif list
  24         [
  25             ast {
  26                 env EVAL
  27             } forall
  28         ]
  29     }{ % else
  30         ast
  31     } ifelse } ifelse
  32 end } def
  33
  34 /EVAL { 3 dict begin
  35     /env exch def
  36     /ast exch def
  37     %(EVAL: ) print ast ==
  38     /arraytype ast type ne { %if not a list
  39         ast env eval_ast
  40     }{ %else apply the list
  41         /el ast env eval_ast def
  42         el _rest % args array
  43         el _first % function
  44         %(vvv\n) print pstack (^^^\n) print
  45         exec % apply function to args
  46     } ifelse
  47 end } def
  48
  49
  50 % print
  51 /PRINT {
  52     true _pr_str
  53 } def
  54
  55
  56 % repl
  57 /repl_env <<
  58     (+) { dup 0 get exch 1 get add }
  59     (-) { dup 0 get exch 1 get sub }
  60     (*) { dup 0 get exch 1 get mul }
  61     (/) { dup 0 get exch 1 get idiv }
  62 >> def
  63
  64 /REP { READ repl_env EVAL PRINT } def
  65
  66 /stdin (%stdin) (r) file def
  67
  68 { % loop
  69     (user> ) print flush
  70
  71     %(%lineedit) (r) file 99 string readline
  72     stdin 99 string readline
  73
  74     not { exit } if  % exit if EOF
  75
  76     %(\ngot line: ) print dup print (\n) print flush
  77
  78     { %try
  79         REP print (\n) print
  80     } stopped {
  81         (Error: ) print
  82         get_error_data false _pr_str print (\n) print
  83         clear
  84     } if
  85 } bind loop
  86
  87 (\n) print  % final newline before exit for cleanliness
  88 quit