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The author was comparing "a" 'a' '' in Python and Haskell. In Haskell, the first one is a list of Char (which happens to be exactly the same thing

The author was comparing "a" 'a' '' in Python and Haskell. In Haskell, the first one is a list of Char (which happens to be exactly the same thing as a String) the second one is a single Char, and the third one doesn't exist because you can't have an empty Char like you can an empty String, because while a String is a list and has a length, which can be zero, a Char is a character, not a list, and simply can't be "empty" in this way. In Python, all these things are strings, and single and double quotes are just alternative syntax for strings. In C you also have a char type and you also have single-quoted char literals, and the third line is a compile-time error in C too for exactly the same reason, because a char literal represents a char, not a list of anything, and so it can't be empty in the way that a string can be empty. From the post: > Python doesn't distinguish between Char and String types with single and double quotes, so empty char is empty string is an empty list. This is basically right, but the subtle misunderstanding here is that there is no such thing an empty char or indeed a char of any kind in Python, the closest you have is chr() and ord() to get integers out of strings. Indexing a string just gives you another string of length one, there's no char type in Python. If you wanted to implement cons, car, and cdr in Python such that (cons (car "abc") (cdr "abc")) = "abc" you wouldn't be able to do it in the natural way, because the type that (car "abc") needs to have doesn't exist in the language. Strings in Python are almost a list type but the elements of that list aren't representable. So, coming from Python, the misunderstanding about why there's no "base case" for char as there is for string is understandable, but it doesn't really have much to do with Haskell or with any kind of runtime error handling.

sweeneyrod 7y ago
> If you wanted to implement cons, car, and cdr in Python such that (cons (car "abc") (cdr "abc")) = "abc" you wouldn't be able to do it in the natural way Sure you can! >>> car = lambda x: x[0] >>> cdr = lambda x: x[1:] >>> cons = lambda x, y: x + y >>> cons (car("abc"), cdr("abc")) 'abc'
- inimino 7y ago
  But that cons is broken, such that you can't construct lists of strings. For a correct implementation of cons, the following gives a list '("a" "b") of two strings: (cons "a" (cons "b" ())) and (list "a" "b") is just sugar for the above. This doesn't work if you redefine cons on strings to mean concat. In other words, if (cons "a" "bc") gives you "abc", then it's not cons.
crimsonalucard 7y ago
I already 100% understand what you're saying. No need to clarify. You're misunderstanding me. >Once you understand that, this confusion makes about as much sense as expecting an integer to be "empty". My comment was in reference to the above. An empty number does make sense because of the of 1/0. There is nothing wrong in including a null in a set if there are operations that are illegal. Such operations can't return something so you can use a null to represent the absence of something. This is entirely different from an empty container type. >So, coming from Python, the misunderstanding about why there's no "base case" for char as there is for string is understandable The author is looking for a null value not an empty container type or "base case". I quote: "Haskell has no null definition of type Char," Basically he's looking for the equivalent of "None" in haskell. He has slight confusion in thinking that an empty container type or empty string is equivalent to a "None." Because he literally said he's looking for a null he is indeed talking about all things associated with null. The closest thing to null in Haskell is the maybe monad which is like null but without a runtime exception. His confusion arises because he feels that if in haskell you can do this: stringfunction (x:xs) = ... stringfunction [] = ... Then you should be able to do this: charfunction x = ... charfunction null = ... which is impossible in haskell, so---> I'm saying that similar functionality can be achieved with: charfunction (Just x) = ... charfunction Nothing = ... The above is 100% handling a null, one of the main sources of runtime errors.
- inimino 7y ago
  We're just pointing out different things. I'm pointing out the different semantics of single-quoted literals as the source of the confusion, with "empty char" being directly mentioned in the post as something that exists in Python, which, as of course you know, it doesn't. If the confusion was about how to add a nothing value to a type, why did it arise specifically in regards to Char, and not, say, Integer? The question "why are the char types different between Haskell and Python in this way" is best answered by pointing out that Python doesn't have a char type at all, and all of these things are strings. Of course, you're entirely correct that you can use a sum type to handle nulls.
  - crimsonalucard 7y ago

sweeneyrod 7y ago

> If you wanted to implement cons, car, and cdr in Python such that (cons (car "abc") (cdr "abc")) = "abc" you wouldn't be able to do it in the natural way Sure you can! >>> car = lambda x: x[0] >>> cdr = lambda x: x[1:] >>> cons = lambda x, y: x + y >>> cons (car("abc"), cdr("abc")) 'abc'

inimino 7y ago
But that cons is broken, such that you can't construct lists of strings. For a correct implementation of cons, the following gives a list '("a" "b") of two strings: (cons "a" (cons "b" ())) and (list "a" "b") is just sugar for the above. This doesn't work if you redefine cons on strings to mean concat. In other words, if (cons "a" "bc") gives you "abc", then it's not cons.

crimsonalucard 7y ago

I already 100% understand what you're saying. No need to clarify. You're misunderstanding me. >Once you understand that, this confusion makes about as much sense as expecting an integer to be "empty". My comment was in reference to the above. An empty number does make sense because of the of 1/0. There is nothing wrong in including a null in a set if there are operations that are illegal. Such operations can't return something so you can use a null to represent the absence of something. This is entirely different from an empty container type. >So, coming from Python, the misunderstanding about why there's no "base case" for char as there is for string is understandable The author is looking for a null value not an empty container type or "base case". I quote: "Haskell has no null definition of type Char," Basically he's looking for the equivalent of "None" in haskell. He has slight confusion in thinking that an empty container type or empty string is equivalent to a "None." Because he literally said he's looking for a null he is indeed talking about all things associated with null. The closest thing to null in Haskell is the maybe monad which is like null but without a runtime exception. His confusion arises because he feels that if in haskell you can do this: stringfunction (x:xs) = ... stringfunction [] = ... Then you should be able to do this: charfunction x = ... charfunction null = ... which is impossible in haskell, so---> I'm saying that similar functionality can be achieved with: charfunction (Just x) = ... charfunction Nothing = ... The above is 100% handling a null, one of the main sources of runtime errors.

inimino 7y ago
We're just pointing out different things. I'm pointing out the different semantics of single-quoted literals as the source of the confusion, with "empty char" being directly mentioned in the post as something that exists in Python, which, as of course you know, it doesn't. If the confusion was about how to add a nothing value to a type, why did it arise specifically in regards to Char, and not, say, Integer? The question "why are the char types different between Haskell and Python in this way" is best answered by pointing out that Python doesn't have a char type at all, and all of these things are strings. Of course, you're entirely correct that you can use a sum type to handle nulls.
- crimsonalucard 7y ago