| Quick nit/question. For the fold method, I don't think I've seen it called sentinel value. Usually it is seed or initial? I think in Scheme it is common to call it knil, mirroring how lists use nil as the "sentinel" value which marks the end of a proper list. I opted to name it sentinel in that article (and in the docs) for two reasons: 1. Sentinel values are a common topic in many languages https://en.wikipedia.org/wiki/Sentinel_value 2. Transducers necessarily abstract across a lot more than loops / lists. Lisps do a lot of really cool (and optimized) stuff with lists alone and Scheme is no different in this regard. However, because of how Scheme primarily exports list operations in (scheme base) is really easy to run into a situation where lists are used in an ad-hoc way where another data structure is more appropriate. This includes vectors, sets, mappings, hashmaps, etc. Transducers-the-library is meant to be general across operations that work on all of these types, so I chose language that intentionally departs from thinking in a list-focused way. Now, my main question. Transducer? I'm curious on the etymology of that word. By itself, I don't think I could ever guess what it was referencing. :( This is from Rich Hickey's presentation: https://www.youtube.com/watch?v=6mTbuzafcII It's not a reducer, because they serve as higher-order functions that operate on reducers. Instead, the values they accept are transient through the function(s), so they transduce. You should watch the video, I think Rich explains the origins of his language very well. |