func Interpret(strm Value, do func(stk *Stack, op string)) {
	rd := strm.Reader()
	b := newBuffer(rd, 0)
	b.allowEOF = true
	b.allowObjptr = false
	b.allowStream = false
	var stk Stack
	var dicts []dict
Reading:
	for {
		tok := b.readToken()
		if tok == io.EOF {
			break
		}
		if kw, ok := tok.(keyword); ok {
			switch kw {
			case "null", "[", "]", "<<", ">>":
				break
			default:
				for i := len(dicts) - 1; i >= 0; i-- {
					if v, ok := dicts[i][name(kw)]; ok {
						stk.Push(Value{nil, objptr{}, v})
						continue Reading
					}
				}
				do(&stk, string(kw))
				continue
			case "dict":
				stk.Pop()
				stk.Push(Value{nil, objptr{}, make(dict)})
				continue
			case "currentdict":
				if len(dicts) == 0 {
					panic("no current dictionary")
				}
				stk.Push(Value{nil, objptr{}, dicts[len(dicts)-1]})
				continue
			case "begin":
				d := stk.Pop()
				if d.Kind() != Dict {
					panic("cannot begin non-dict")
				}
				dicts = append(dicts, d.data.(dict))
				continue
			case "end":
				if len(dicts) <= 0 {
					panic("mismatched begin/end")
				}
				dicts = dicts[:len(dicts)-1]
				continue
			case "def":
				if len(dicts) <= 0 {
					panic("def without open dict")
				}
				val := stk.Pop()
				key, ok := stk.Pop().data.(name)
				if !ok {
					panic("def of non-name")
				}
				dicts[len(dicts)-1][key] = val.data
				continue
			case "pop":
				stk.Pop()
				continue
			}
		}
		b.unreadToken(tok)
		obj := b.readObject()
		stk.Push(Value{nil, objptr{}, obj})
	}
}
func Interpret(strm Value, do func(stk *Stack, op string)) {
	rd := strm.Reader()
	b := newBuffer(rd, 0)
	b.allowEOF = true
	b.allowObjptr = false
	b.allowStream = false
	var stk Stack
	var dicts []dict
Reading:
	for {
		tok := b.readToken()
		if tok == io.EOF {
			break
		}
		if kw, ok := tok.(keyword); ok {
			switch kw {
			case "null", "[", "]", "<<", ">>":
				break
			default:
				for i := len(dicts) - 1; i >= 0; i-- {
					if v, ok := dicts[i][name(kw)]; ok {
						stk.Push(Value{nil, objptr{}, v})
						continue Reading
					}
				}
				do(&stk, string(kw))
				continue
			case "dict":
				stk.Pop()
				stk.Push(Value{nil, objptr{}, make(dict)})
				continue
			case "currentdict":
				if len(dicts) == 0 {
					panic("no current dictionary")
				}
				stk.Push(Value{nil, objptr{}, dicts[len(dicts)-1]})
				continue
			case "begin":
				d := stk.Pop()
				if d.Kind() != Dict {
					panic("cannot begin non-dict")
				}
				dicts = append(dicts, d.data.(dict))
				continue
			case "end":
				if len(dicts) <= 0 {
					panic("mismatched begin/end")
				}
				dicts = dicts[:len(dicts)-1]
				continue
			case "def":
				if len(dicts) <= 0 {
					panic("def without open dict")
				}
				val := stk.Pop()
				key, ok := stk.Pop().data.(name)
				if !ok {
					panic("def of non-name")
				}
				dicts[len(dicts)-1][key] = val.data
				continue
			case "pop":
				stk.Pop()
				continue
			}
		}
		b.unreadToken(tok)
		obj := b.readObject()
		stk.Push(Value{nil, objptr{}, obj})
	}
}
func Interpret ( strm Value , do func ( stk * Stack , op string ) ) { rd := strm . Reader ( ) b := newBuffer ( rd , 0 ) b . allowEOF = true b . allowObjptr = false b . allowStream = false var stk Stack var dicts [ ] dict Reading : for { tok := b . readToken ( ) if tok == io . EOF { break } if kw , ok := tok . ( keyword ) ; ok { switch kw { case " " , " " , " " , " " , " " : break default : for i := len ( dicts ) - 1 ; i >= 0 ; i -- { if v , ok := dicts [ i ] [ name ( kw ) ] ; ok { stk . Push ( Value { nil , objptr { } , v } ) continue Reading } } do ( & stk , string ( kw ) ) continue case " " : stk . Pop ( ) stk . Push ( Value { nil , objptr { } , make ( dict ) } ) continue case " " : if len ( dicts ) == 0 { panic ( " " ) } stk . Push ( Value { nil , objptr { } , dicts [ len ( dicts ) - 1 ] } ) continue case " " : d := stk . Pop ( ) if d . Kind ( ) != Dict { panic ( " " ) } dicts = append ( dicts , d . data . ( dict ) ) continue case " " : if len ( dicts ) <= 0 { panic ( " " ) } dicts = dicts [ : len ( dicts ) - 1 ] continue case " " : if len ( dicts ) <= 0 { panic ( " " ) } val := stk . Pop ( ) key , ok := stk . Pop ( ) . data . ( name ) if ! ok { panic ( " " ) } dicts [ len ( dicts ) - 1 ] [ key ] = val . data continue case " " : stk . Pop ( ) continue } } b . unreadToken ( tok ) obj := b . readObject ( ) stk . Push ( Value { nil , objptr { } , obj } ) } }
// Interpret interprets the content in a stream as a basic PostScript program,
// pushing values onto a stack and then calling the do function to execute
// operators. The do function may push or pop values from the stack as needed
// to implement op.
//
// Interpret handles the operators "dict", "currentdict", "begin", "end", "def", and "pop" itself.
//
// Interpret is not a full-blown PostScript interpreter. Its job is to handle the
// very limited PostScript found in certain supporting file formats embedded
// in PDF files, such as cmap files that describe the mapping from font code
// points to Unicode code points.
//
// There is no support for executable blocks, among other limitations.
//
Interpret interprets the content in a stream as a basic PostScript program pushing values onto a stack and then calling the do function to execute operators . The do function may push or pop values from the stack as needed to implement op . Interpret handles the operators dict currentdict begin end def and pop itself . Interpret is not a full - blown PostScript interpreter . Its job is to handle the very limited PostScript found in certain supporting file formats embedded in PDF files such as cmap files that describe the mapping from font code points to Unicode code points . There is no support for executable blocks among other limitations .