ps/step4_if_fn_do.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 env_get
  18     }{ /arraytype ast type eq { %elseif list
  19         [
  20             ast {
  21                 env EVAL
  22             } forall
  23         ]
  24     }{ % else
  25         ast
  26     } ifelse } ifelse
  27 end } def
  28
  29 /EVAL { 10 dict begin
  30     /env exch def
  31     /ast exch def
  32     %(EVAL: ) print ast ==
  33     /arraytype ast type ne { %if not a list
  34         ast env eval_ast
  35     }{ %else apply the list
  36         /a0 ast 0 get def
  37         /def! a0 eq { %if def!
  38             /a1 ast 1 get def
  39             /a2 ast 2 get def
  40             env a1  a2 env EVAL  env_set
  41         }{ /let* a0 eq { %if let*
  42             /a1 ast 1 get def
  43             /a2 ast 2 get def
  44             /let_env env [ ] [ ] env_new def
  45             0 2 a1 length 1 sub { %for each pair
  46                 /idx exch def
  47                 let_env
  48                     a1 idx get
  49                     a1 idx 1 add get let_env EVAL
  50                     env_set
  51             } for
  52             a2 let_env EVAL
  53         }{ /do a0 eq { %if do
  54             /el ast _rest env eval_ast def
  55             el el length 1 sub get % return last value
  56         }{ /if a0 eq { %if if
  57             /a1 ast 1 get def
  58             /cond a1 env EVAL def
  59             cond null eq cond false eq or { % if cond is nil or false
  60                 ast length 3 gt { %if false branch (a3) provided
  61                     ast 3 get env EVAL % EVAL false branch (a3)
  62                 }{
  63                     null
  64                 } ifelse
  65             }{
  66                 ast 2 get env EVAL % EVAL true branch (a2)
  67             } ifelse
  68         }{ /fn* a0 eq { %if fn*
  69             /a1 ast 1 get def
  70             /a2 ast 2 get def
  71             { 4 dict begin
  72                 /A1  __a1__  def % close over positino 4
  73                 /A2  __a2__  def % close over position 7
  74                 /ENV __env__ def % close over position 10
  75                 /args exch def
  76                 %(inside fn*:\n) print
  77                 %(  A1: ) print A1 ==
  78                 %(  A2: ) print A2 ==
  79                 %(  ENV: ) print ENV ==
  80                 %(  args: ) print args ==
  81                 A2   ENV A1 args env_new   EVAL
  82             end }
  83             dup length array copy cvx % make an actual copy/new instance
  84             dup 4 a1 put   % insert closed over a1 into position 4
  85             dup 7 a2 put   % insert closed over a1 into position 7
  86             dup 10 env put % insert closed over a1 into position 10
  87         }{
  88             /el ast env eval_ast def
  89             el _rest % args array
  90             el _first cvx % function
  91             %(vvv\n) print pstack (^^^\n) print
  92             exec % apply function to args
  93         } ifelse } ifelse } ifelse } ifelse } ifelse
  94     } ifelse
  95 end } def
  96
  97
  98 % print
  99 /PRINT {
 100     true _pr_str
 101 } def
 102
 103
 104 % repl
 105 /repl_env null [ ] [ ] env_new def
 106
 107 /RE { READ repl_env EVAL } def
 108 /REP { READ repl_env EVAL PRINT } def
 109 /_ref { repl_env 3 1 roll env_set pop } def
 110
 111 types_ns { _ref } forall
 112
 113 (\(def! not \(fn* \(a\) \(if a false true\)\)\)) RE pop
 114
 115 /stdin (%stdin) (r) file def
 116
 117 { % loop
 118     (user> ) print flush
 119
 120     %(%lineedit) (r) file 99 string readline
 121     stdin 99 string readline
 122
 123     not { exit } if  % exit if EOF
 124
 125     %(\ngot line: ) print dup print (\n) print flush
 126
 127     { %try
 128         REP print (\n) print
 129     } stopped {
 130         (Error: ) print
 131         get_error_data false _pr_str print (\n) print
 132         clear
 133     } if
 134 } bind loop
 135
 136 (\n) print  % final newline before exit for cleanliness
 137 quit