3 ms·

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 t

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.

runeks 9y ago
I agree. From the article: > 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 means that you can construct a value of type Bool using one of the constructors True or False.
- danieldk 9y ago
  But the constructor approach does not explain what makes a sum type a sum. 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; } This is a so-called product type, because the number of possible values of Foo is the number of values of type X times the number of values of type Y. So if X = {Red, Green, Blue} and Y = {Light, Dark}, then this product type has 3 x 2 = 6 different values: Foo {Red, Light} Foo {Green, Light} Foo {Blue, Light} Foo {Red, Dark} Foo {Green, Dark} Foo {Blue, Dark} What if instead, we wanted to have the sum of the possible values of X and Y? In other words, where we'd have to choose between a value from X or from Y? Foo {Red} Foo {Green} Foo {Blue} Foo {Light} Foo {Dark} That's a sum type: it is a type where you can pick a value from X or Y, giving a total of 3 + 2 = 5 possible values. Then give a motivating example where one would need such a type (e.g. trees nodes) and introduce proper notation.
  - hcs 9y ago
    I agree with your approach, one suggestion: If you're using struct to introduce product, does it make sense to use union to explain sum? Although maybe that's too complicated given the need to tag it?
- moomin 9y ago
  I think you're missing the point between a teaching article and an article about teaching. This is in the latter category.
nightski 9y ago
Not defending the OP but at the same time I've never approached a brand new subject and had a textbook or similar resource which walked me through it perfectly without having to look up words I did not understand or reference other materials. That is kind of just part of the process. Having subjected myself to the world of machine learning over the past several years I can tell you I constantly encountered things I did not understand, so much so that it became routine to just go look it up and move on.
- shakna 9y ago
  > I've never approached a brand new subject and had a textbook or similar resource which walked me through it perfectly without having to look up words I did not understand or reference other materials. 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. [0] http://norvig.com/lispy.html http://norvig.com/lispy.html
  - nightski 9y ago
    If you are going to limit learning to resources perfectly catered to your level of knowledge, then you are missing out on a lot. It's really not hard to go look up a few terms.
    - shakna 9y ago
      And equally, if you delve blindly in areas where you don't have the knowledge, you're going to be seriously handicapped. 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.
sizeofchar 9y ago
I, too, found it incredibly confuse from the very beginning... And I know a bit of Haskell already!

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.

runeks 9y ago

I agree. From the article: > 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 means that you can construct a value of type Bool using one of the constructors True or False.

danieldk 9y ago
But the constructor approach does not explain what makes a sum type a sum. 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; } This is a so-called product type, because the number of possible values of Foo is the number of values of type X times the number of values of type Y. So if X = {Red, Green, Blue} and Y = {Light, Dark}, then this product type has 3 x 2 = 6 different values: Foo {Red, Light} Foo {Green, Light} Foo {Blue, Light} Foo {Red, Dark} Foo {Green, Dark} Foo {Blue, Dark} What if instead, we wanted to have the sum of the possible values of X and Y? In other words, where we'd have to choose between a value from X or from Y? Foo {Red} Foo {Green} Foo {Blue} Foo {Light} Foo {Dark} That's a sum type: it is a type where you can pick a value from X or Y, giving a total of 3 + 2 = 5 possible values. Then give a motivating example where one would need such a type (e.g. trees nodes) and introduce proper notation.
- hcs 9y ago
  I agree with your approach, one suggestion: If you're using struct to introduce product, does it make sense to use union to explain sum? Although maybe that's too complicated given the need to tag it?
moomin 9y ago
I think you're missing the point between a teaching article and an article about teaching. This is in the latter category.

nightski 9y ago

Not defending the OP but at the same time I've never approached a brand new subject and had a textbook or similar resource which walked me through it perfectly without having to look up words I did not understand or reference other materials. That is kind of just part of the process. Having subjected myself to the world of machine learning over the past several years I can tell you I constantly encountered things I did not understand, so much so that it became routine to just go look it up and move on.

shakna 9y ago
> I've never approached a brand new subject and had a textbook or similar resource which walked me through it perfectly without having to look up words I did not understand or reference other materials. 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. [0] http://norvig.com/lispy.html http://norvig.com/lispy.html
- nightski 9y ago
  If you are going to limit learning to resources perfectly catered to your level of knowledge, then you are missing out on a lot. It's really not hard to go look up a few terms.
  - shakna 9y ago
    And equally, if you delve blindly in areas where you don't have the knowledge, you're going to be seriously handicapped. 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.

sizeofchar 9y ago

I, too, found it incredibly confuse from the very beginning... And I know a bit of Haskell already!