functor, sum type, recursively defined.
This teaching opportunity is already lost. Who are you teaching to? Someone new to programming is going to be lost by the first example.
This teaching opportunity is already lost. Who are you teaching to? Someone new to programming is going to be lost by the first example.
> The | operator indicates that this is a sum type [..]
This doesn't explain what's going on; it references terminology used only by people who already know what's going on.
A pedagogical explanation would say: the | operator means "or", in that you can use multiple different constructors (separated by |) to construct the type in question (whose name is to the left of the '=' operator). For example:
data Bool = True | False
If the readers already have some background in a programming language, you could also start with e.g. a struct from an imperative language:
struct Foo {
X x;
Y y;
}
Foo {Red, Light}
Foo {Green, Light}
Foo {Blue, Light}
Foo {Red, Dark}
Foo {Green, Dark}
Foo {Blue, Dark}
Foo {Red}
Foo {Green}
Foo {Blue}
Foo {Light}
Foo {Dark}
Then give a motivating example where one would need such a type (e.g. trees nodes) and introduce proper notation.
Never? That sounds like you've always been taught things the hard way.
I learned about Pi by nearly the same method of Pythagoras.
Methods come first, and the words come later. Build upon the knowledge people have, don't just plop a steaming pile of high level concepts in their lap and expect them to figure it out.
I'm sorry you've never really seen that before, but it's how I see all the greats explain things.
Take for example, Novig's Lisp interpreter in Python [0], he does expect some back knowledge. But he explains the core ideas, and then each new idea introduced just expands on the previous.
We don't teach physics to those who have never been exposed to algebra, and you can't explain the half life of uranium to someone who doesn't know what an atom is.
In practice, we can and do explain... By giving the basics.
The beginner who tries to understand the Dragon Book, will get somewhere. They will be enhanced.
But nearly as much as if they'd read Lisp In Small Pieces.
I have plenty of technical manuals on my shelves. Once, they were utterly useless. Knowledge made them tools. But a beginner can't just leap into Intel's x86 instruction manual and expect it will help, if they don't understand registers, pointers, and that a cpu has a cache.