It does present a series of case studies that (I recall) are around 500 lines, but it's not so easy to count because the code is interleaved with explanation.
Although the code in each study is mostly self contained, the presentation is not -- the later studies depend on ideas and techniques introduced in the earlier ones, so it works best of you go through the book from beginning to end.
The code is very bare bones - it's all in the Scheme language, with no user interface except the Scheme REPL.