Sam Danielson

Write yourself a Scheme in 48 Hours

This is the most excited I’ve been since I learned how to make a character bounce around the screen on my C64! Learning a new programming style is hard: big programs are difficult to understand and small programs have too little to tweak. How do I learn from a ten line tutorial or a one-hundred line program? The ten line tutorial doesn’t do anything interesting and forces me to write new code to grow. OTOH, one-hundred lines of Haskell usually do something neat but I can’t begin to untangle how. For everyone there is a threshold of complexity, the understanding of which enables creating more complex things. Once this threshold is achieved a person can bootstrap their learning as an autodidact. Below it there is neither enough knowledge to guide their study or test their knowledge for correctness.

My capacity for understanding is often far lower than the bootstrapping threshold and my learning stalls as I fumble through tutorials gaining one small bit of knowledge without correlation until one day things begin to click into place. I then wonder how I learned in eight hours what had stumped me for eight months and feel profound appreciation for the wizards that understood it first. It’s like I was blind and they could see, and now through some miracle I also see. It’s real sight too, not just a description in words but the real sunrise seen for the first time by the formerly blind. In this case the misfitting pieces were the static algebraic types, monads, type classes, currying, and lazy evaluation of Haskell. It’s quite a bit to swallow just as the more familiar loops, conditional statements, functions, and variables once were. Many of these things are interdependent and cannot be understood separately. Jonathan Tang begins small and works from the ground up to a larger program, explaining each change so every line’s purpose is thoroughly understood. The culmination is a very small but capable scheme interpreter that is larger than what I would have understood without my building it. It is a perfect demonstration of the building-block technique of instruction I learned and used as a flight instructor.

Mr. Tang put the pieces together concisely. Wow.