I also blog frequently on the Yesod Web Framework blog, as well as the FP Complete blog.

Kids Coding, Part 2

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I didn’t expect to be writing the second blog post only 12 hours after the first. But when the kids came downstairs this morning, they were unbelievably excited to do more coding. So here we are!

Eliezer and I discussed using more visual tooling (like Code World or Jupiter) for doing the learning, and I showed him what it looked like. It seems he’s got quite a bit of his father’s preferences, and wanted to stick to plain text for now. We’ll probably circle back to that kind of stuff after they get the basics. It will also give me a chance to get more comfortable with those offerings. (Thanks all for the recommendations on Reddit.)

One final note. I’m extremely happy that we went with Haskell after today’s lessons. Concepts like variable replacement which are natural in Haskell were great teaching tools. I obviously don’t have enough data to prove this yet, but I’m more strongly believing the long-held theory that Haskell is easier for brand new programmers than those familiar with imperative programming.

Coding environment

I moved us over to VSCode, with only syntax highlighting set up. Previously, I’d used my emacs setup with intero, and the red squiggles let them know they’d messed up too early. I used the docked terminal at the bottom, taught them to save, and showed them to press “up enter” in the terminal to rerun stack runghc foo.hs. Perhaps not the ideal setup, but definitely good enough.


  • Started with main = print "hello world"

  • Explained that main is defined as other thing

  • Expanded to

    main = print hello
    hello = "hello world"
  • They were not surprised at all that this just worked

  • hello = 5 + 6, both got confused about whether it would print 11 or 5 + 6, reminded them of strings

  • How about hello = five + six?

  • Both agreed it wouldn’t work. I typed in five = 5, and ask if it would work. They agree that it won’t, and I show them GHC’s error message.

  • “Variable not in scope.” Computers talk funny, just means “I don’t know what six is.” Instilled that they’ll eventually be able to understand those massive error messages, but not to worry about it yet.

  • Exercise: five the program. Both of them got it no problem.

  • I was about to demonstrate five = 4, and then Gavriella figured it out for herself! They understand that, again, “computers are dumb.” Names are just there for our benefit, computer doesn’t care.

  • We do five + six * seven (with appropriate variable definitions), they get that answer, and then (five + six) * seven, they get that too.

  • Now I define fivePlusSix = five + six, and change to hello = (fivePlusSix) * seven (direct replacement). They’re fine with this. Yay replacement.

  • Point out that the parens are now unneeded and remove them. Again, no problem.

  • Parens just tell us “do this first”, not needed for one thing


  • Type in hello = 5 * 2, no problem.
  • How about hello = double 5? They figured out that it won’t work cuz computers be dumb
  • How do we define double? Eliezer guessed * 2, which is really close, but we’re not ready for sections, and I want to teach standard function stuff first.
  • Show them double x = x * 2, that x is a variable, and a function argument. They don’t know algebra yet, but got this fairly quickly.
  • hello = addFive (double 5)
  • Exercise: fix the program!
  • Eliezer did this one, defined addFive, and he started spacing things like me without any prompting. Cool.
  • Exercise: Gavriella, write minusTwo
  • Got it first time, ran it, answer’s still 15. Why?
  • We stepped through how the program is evaluated. “Let’s look at main, oh, I got an action! I need to print hello, what’s that? Oh, it’s addFive .... That means I gotta figure out .... What’s double 5? Oh, it’s 10. So that’s 15. And minusTwo was never (terminology break, I taught them that it wasn’t used).
  • Exercise: make the answer 13. They’re struggling to figure out where to use it. They’re stumped, time to jump in.
  • Stepped through all of the types involved. “double is a function that takes a number and gives you back a number” blah blah blah
  • minusTwo is also a function. It needs one number. Let’s try something wrong: minusTwo addFive (double 5). That’s wrong: it means “apply minusTwo to two values” but it only needs one number.
  • We need to turn addFive (double 5) into one thing. Ask them what we can use. They played with idea of double quotes, and then they figured out the parens! Awesome!
  • One final exercise: make the answer 16 with plus3
  • Eliezer did that typing, so I gave Gavriella one real final one: make the answer 6 with minusTen. She did it.
  • Realizing now: learning to type and navigate an editor is possibly harder for them than the coding itself


Gavriella kept playing with the code (wow, she’s focused on this). She decided she wanted to do division. That was more complicated, but she persevered. I taught her about div being a function that takes 2 arguments. She didn’t know anything about remainders, and was confused that div 15 2 worked at all. I taught her about divMod, and she did great.

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