requires: {#PositionableStream. #Trie}.
provides: {#LZWReadStream. #LZWWriteStream}.

prototypes addPrototype: #LZWReadStream derivedFrom: {PositionableReadStream}.
"A ReadStream which reads from another stream some LZW-compressed data and
outputs the decompressed contents."
LZWReadStream addSlot: #source valued: ReadStream clone.
"The stream from which the values are read."
LZWReadStream addSlot: #strings valued: Trie newEmpty.
"The set of sequences seen so far; the codes are stored at the leaves."
LZWReadStream addSlot: #currentString.

lz@(LZWReadStream traits) on: s
[
  lz source: s.
  lz strings: lz strings newEmpty.
  lz currentString: lz strings.
  lz
].

lz@(LZWReadStream traits) wordSize
[
  lz source wordSize
].

lz@(LZWReadStream traits) next
[| nextChar |
  nextChar: lz source next.
  
].

prototypes addPrototype: #LZWWriteStream derivedFrom: {PositionableWriteStream}.
"A WriteStream which writes out data in an LZW-compressed form. The flush
method actually causes the write to occur, since a dictionary needs to be built
up first to encode the data."
LZWWriteStream addSlot: #source valued: ReadStream clone.
"The stream to which the compressed values are written."
LZWReadStream addSlot: #strings valued: Trie newEmpty.
"The set of sequences seen so far; the codes are stored at the leaves."
LZWReadStream addSlot: #currentString.