ps/step2_eval.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_ast { 2 dict begin
  17     /env exch def
  18     /ast exch def
  19     %(eval_ast: ) print ast ==
  20     ast _symbol? { %if symbol
  21         env ast known {
  22             env ast get
  23         }{
  24             (') ast false _pr_str (' not found)
  25             concatenate concatenate _throw
  26         } ifelse
  27     }{ ast _sequential? { %elseif list or vector
  28         [
  29             ast /data get { %forall items
  30                 env EVAL
  31             } forall
  32         ] ast _list? { _list_from_array }{ _vector_from_array } ifelse
  33     }{ ast _hash_map? { %elseif list or vector
  34         <<
  35             ast /data get { %forall entries
  36                 env EVAL
  37             } forall
  38         >> _hash_map_from_dict
  39     }{ % else
  40         ast
  41     } ifelse } ifelse } ifelse
  42 end } def
  43
  44 /EVAL { 3 dict begin
  45     /env exch def
  46     /ast exch def
  47
  48     %(EVAL: ) print ast true _pr_str print (\n) print
  49     ast _list? not { %if not a list
  50         ast env eval_ast
  51     }{ %else apply the list
  52         /el ast env eval_ast def
  53         el _rest el _first % stack: ast function
  54         exec % apply function to args
  55     } ifelse
  56 end } def
  57
  58
  59 % print
  60 /PRINT {
  61     true _pr_str
  62 } def
  63
  64
  65 % repl
  66 /repl_env <<
  67     (+) { dup 0 _nth exch 1 _nth add }
  68     (-) { dup 0 _nth exch 1 _nth sub }
  69     (*) { dup 0 _nth exch 1 _nth mul }
  70     (/) { dup 0 _nth exch 1 _nth idiv }
  71 >> def
  72
  73 /REP { READ repl_env EVAL PRINT } def
  74
  75 % repl loop
  76 { %loop
  77     (user> ) _readline
  78     not { exit } if  % exit if EOF
  79
  80     { %try
  81         REP print (\n) print
  82     } stopped {
  83         (Error: ) print
  84         get_error_data false _pr_str print (\n) print
  85         $error /newerror false put
  86         $error /errorinfo null put
  87         clear
  88         cleardictstack
  89     } if
  90 } bind loop
  91
  92 (\n) print  % final newline before exit for cleanliness
  93 quit