Data commit

Task/LZW-compression/Dylan/lzw-compression.dylan

@@ -0,0 +1,43 @@
+Module:   LZW
+Synopsis: LZW implementation for Rosetta code
+
+define method output(n :: <integer>)
+  format-out("%d ", n);
+end;
+
+define method contains?(dict, var)
+  let x = element(dict, var, default: #f);
+  x ~= #f;
+end;
+
+define method byte->string(c)
+  add("", as(<character>, c));
+end;
+
+define method compress(input :: <string>) => <vector>;
+  let result = make(<vector>);
+  let dict = make(<string-table>);
+  for (x from 0 to 255)
+    dict[byte->string(x)] := x;
+  end;
+
+  let next-code = 256;
+  let cur-seq = "";
+  for (c in input)
+    let wc = add(cur-seq, c);
+    if (contains?(dict, wc))
+      cur-seq := wc;
+    else
+      result := add(result, dict[cur-seq]);
+      dict[wc] := next-code;
+      next-code := next-code + 1;
+      cur-seq := add("", c);
+    end
+  end;
+  unless (empty?(cur-seq))
+    result := add(result, dict[cur-seq]);
+  end;
+  result
+end;
+
+format-out("%=\n", compress("TOBEORNOTTOBEORTOBEORNOT"))