ps/step4_if_fn_do.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 (core.ps) runlibfile
   7
   8 % read
   9 /_readline { print flush (%stdin) (r) file 1024 string readline } def
  10
  11 /READ {
  12     /str exch def
  13     str read_str
  14 } def
  15
  16
  17 % eval
  18 /eval_ast { 2 dict begin
  19     /env exch def
  20     /ast exch def
  21     %(eval_ast: ) print ast ==
  22     ast _symbol? { %if symbol
  23         env ast env_get
  24     }{ ast _sequential? { %elseif list or vector
  25         [
  26             ast /data get { %forall items
  27                 env EVAL
  28             } forall
  29         ] ast _list? { _list_from_array }{ _vector_from_array } ifelse
  30     }{ ast _hash_map? { %elseif list or vector
  31         <<
  32             ast /data get { %forall entries
  33                 env EVAL
  34             } forall
  35         >> _hash_map_from_dict
  36     }{ % else
  37         ast
  38     } ifelse } ifelse } ifelse
  39 end } def
  40
  41 /EVAL { 9 dict begin
  42     /env exch def
  43     /ast exch def
  44
  45     %(EVAL: ) print ast true _pr_str print (\n) print
  46     ast _list? not { %if not a list
  47         ast env eval_ast
  48     }{ %else apply the list
  49         /a0 ast 0 _nth def
  50         a0 _nil? { %if ()
  51             ast
  52         }{ /def! a0 eq { %if def!
  53             /a1 ast 1 _nth def
  54             /a2 ast 2 _nth def
  55             env a1  a2 env EVAL  env_set
  56         }{ /let* a0 eq { %if let*
  57             /a1 ast 1 _nth def
  58             /a2 ast 2 _nth def
  59             /let_env env null null env_new def
  60             0 2 a1 _count 1 sub { %for each pair
  61                 /idx exch def
  62                 let_env
  63                     a1 idx _nth
  64                     a1 idx 1 add _nth let_env EVAL
  65                     env_set
  66                     pop % discard the return value
  67             } for
  68             a2 let_env EVAL
  69         }{ /do a0 eq { %if do
  70             /el ast _rest env eval_ast def
  71             el el _count 1 sub _nth % return last value
  72         }{ /if a0 eq { %if if
  73             /a1 ast 1 _nth def
  74             /cond a1 env EVAL def
  75             cond null eq cond false eq or { % if cond is nil or false
  76                 ast _count 3 gt { %if false branch with a3
  77                     ast 3 _nth env
  78                     EVAL
  79                 }{ % else false branch with no a3
  80                     null
  81                 } ifelse
  82             }{ % true branch
  83                 ast 2 _nth env
  84                 EVAL
  85             } ifelse
  86         }{ /fn* a0 eq { %if fn*
  87             /a1 ast 1 _nth def
  88             /a2 ast 2 _nth def
  89             a2 env a1 _mal_function
  90         }{
  91             /el ast env eval_ast def
  92             el _rest el _first % stack: ast function
  93             dup _mal_function? { %if user defined function
  94                 fload % stack: ast new_env
  95                 EVAL
  96             }{ dup _function? { %else if builtin function
  97                 /data get exec
  98             }{ %else (regular procedure/function)
  99                 (cannot apply native proc!\n) print quit
 100             } ifelse } ifelse
 101         } ifelse } ifelse } ifelse } ifelse } ifelse } ifelse
 102     } ifelse
 103 end } def
 104
 105
 106 % print
 107 /PRINT {
 108     true _pr_str
 109 } def
 110
 111
 112 % repl
 113 /repl_env null null null env_new def
 114
 115 /RE { READ repl_env EVAL } def
 116 /REP { READ repl_env EVAL PRINT } def
 117
 118 % core.ps: defined using postscript
 119 /_ref { repl_env 3 1 roll env_set pop } def
 120 core_ns { _function _ref } forall
 121
 122 % core.mal: defined using the language itself
 123 (\(def! not \(fn* \(a\) \(if a false true\)\)\)) RE pop
 124
 125 % repl loop
 126 { %loop
 127     (user> ) _readline
 128     not { exit } if  % exit if EOF
 129
 130     { %try
 131         REP print (\n) print
 132     } stopped {
 133         (Error: ) print
 134         get_error_data false _pr_str print (\n) print
 135         $error /newerror false put
 136         $error /errorinfo null put
 137         clear
 138         cleardictstack
 139     } if
 140 } bind loop
 141
 142 (\n) print  % final newline before exit for cleanliness
 143 quit