ps/step3_env.ps

   1 /runlibfile where { pop }{ /runlibfile { run } def } ifelse %
   2 (types.ps) runlibfile
   3 (reader.ps) runlibfile
   4 (printer.ps) runlibfile
   5 (env.ps) runlibfile
   6
   7 % read
   8 /_readline { print flush (%stdin) (r) file 1024 string readline } def
   9
  10 /READ {
  11     /str exch def
  12     str read_str
  13 } def
  14
  15
  16 % eval
  17 /eval_ast { 2 dict begin
  18     /env exch def
  19     /ast exch def
  20     %(eval_ast: ) print ast ==
  21     ast _symbol? { %if symbol
  22         env ast env_get
  23     }{ ast _sequential? { %elseif list or vector
  24         [
  25             ast /data get { %forall items
  26                 env EVAL
  27             } forall
  28         ] ast _list? { _list_from_array }{ _vector_from_array } ifelse
  29     }{ ast _hash_map? { %elseif list or vector
  30         <<
  31             ast /data get { %forall entries
  32                 env EVAL
  33             } forall
  34         >> _hash_map_from_dict
  35     }{ % else
  36         ast
  37     } ifelse } ifelse } ifelse
  38 end } def
  39
  40 /EVAL { 8 dict begin
  41     /env exch def
  42     /ast exch def
  43
  44     %(EVAL: ) print ast true _pr_str print (\n) print
  45     ast _list? not { %if not a list
  46         ast env eval_ast
  47     }{ %else apply the list
  48         /a0 ast 0 _nth def
  49         a0 _nil? { %if ()
  50             ast
  51         }{ /def! a0 eq { %if def!
  52             /a1 ast 1 _nth def
  53             /a2 ast 2 _nth def
  54             env a1  a2 env EVAL  env_set
  55         }{ /let* a0 eq { %if let*
  56             /a1 ast 1 _nth def
  57             /a2 ast 2 _nth def
  58             /let_env env null null env_new def
  59             0 2 a1 _count 1 sub { %for each pair
  60                 /idx exch def
  61                 let_env
  62                     a1 idx _nth
  63                     a1 idx 1 add _nth let_env EVAL
  64                     env_set
  65                     pop % discard the return value
  66             } for
  67             a2 let_env EVAL
  68         }{
  69             /el ast env eval_ast def
  70             el _rest el _first % stack: ast function
  71             exec % apply function to args
  72         } ifelse } ifelse } ifelse
  73     } ifelse
  74 end } def
  75
  76
  77 % print
  78 /PRINT {
  79     true _pr_str
  80 } def
  81
  82
  83 % repl
  84 /repl_env null null null env_new def
  85
  86 /REP { READ repl_env EVAL PRINT } def
  87
  88 /_ref { repl_env 3 1 roll env_set pop } def
  89 (+) { dup 0 _nth exch 1 _nth add } _ref
  90 (-) { dup 0 _nth exch 1 _nth sub } _ref
  91 (*) { dup 0 _nth exch 1 _nth mul } _ref
  92 (/) { dup 0 _nth exch 1 _nth idiv } _ref
  93
  94 % repl loop
  95 { %loop
  96     (user> ) _readline
  97     not { exit } if  % exit if EOF
  98
  99     { %try
 100         REP print (\n) print
 101     } stopped {
 102         (Error: ) print
 103         get_error_data false _pr_str print (\n) print
 104         $error /newerror false put
 105         $error /errorinfo null put
 106         clear
 107         cleardictstack
 108     } if
 109 } bind loop
 110
 111 (\n) print  % final newline before exit for cleanliness
 112 quit