SimpleIO in JEP draft 8323335
forax at univ-mlv.fr
forax at univ-mlv.fr
Tue Feb 20 17:59:28 UTC 2024
Hello Cay,
----- Original Message -----
> From: "Cay Horstmann" <cay at horstmann.com>
> To: "Brian Goetz" <brian.goetz at oracle.com>, "Remi Forax" <forax at univ-mlv.fr>, "Tagir Valeev" <amaembo at gmail.com>
> Cc: "amber-dev" <amber-dev at openjdk.org>
> Sent: Tuesday, February 20, 2024 12:44:53 PM
> Subject: Re: SimpleIO in JEP draft 8323335
> I am one of the people who writes books for beginners. I have a whole bunch of
> example programs that involve reading numbers. Professors adopting my books
> have a ton of exercises that involve reading numbers. I can't ignore reading
> numbers.
>
> I agree that input and println are reasonable primitives for beginners, and that
> number parsing can be done in a separate step. But if that parsing step is not
> simple for beginners, I don't think input will find much use for beginners
> either.
>
> For my books, I need to decide what to do in the (n + 1)st edition. Should I
> stick with
>
> Scanner in = new Scanner(System.in);
> ...
> System.out.print("How old are you? ");
> int age = in.nextInt();
>
> or switch to
>
> println("How old are you?");
> int age = in.nextInt();
>
> or go all the way to
>
> int age = Integer.parseInt(input("How old are you"));
Showing my age, you can also a version with a StringTokenizer :)
>
> I have no conceptual problem with in.nextInt(). I need to explain method calls
> early on, so that students can work with strings.
Scanner requires quite a lot concepts, you need to explain "import" (it's in java.util), "new" and instance method calls.
>
> With the new way, I have a different problem. Now I need to explain to students
> that they can call an unqualified input, but parseInt needs to be qualified.
> And I have to accelerate the coverage of static methods.
Using a static method is quite different than declaring a static method.
To use a static method, you just need to explain that functions in Java belong to a name,
it's not sin() but Math.sin(), it's not parseInt() but Integer.parseInt().
>
> As Brian says, there are too many conflicting goals.
>
> If the goal is simplicity and consistency, it would be more useful not to use a
> magic static import. If SimpleIO.input is too long, it could be IO.in, with IO
> in java.lang.
You can have both. You can start by using println() and readln() and works with functions.
Then explain that in fact, println() is SimpleIO.println() when you introduce Math.sin() and Integer.parseInt().
Exactly like later, when you explain import, you explain that String is in fact java.lang.String.
>
> If the goal is convenience, it would be better to have more magically statically
> imported methods, in particular parseInt, parseDouble. Or readAnInt,
> readADouble...
It looks like a false dichotomy to me.
>
> Cheers,
>
> Cay
Rémi
>
>
> On 19/02/2024 18.06, Brian Goetz wrote:
>> There's a reason there are so many opinions here: because the goals are in
>> conflict. Everyone wants simplicity, but people don't agree on what "simple"
>> means. (Cue the jokes about "I would simply not write programs with bugs.")
>>
>> Yes, getting numbers from the user is a basic task. But it is not, in any way,
>> simple! Because reading numbers from the input is invariably complected with
>> discarding things that are "acceptably non-numbery" (e.g., whitespace), which
>> is neither simple nor usually terribly well documented. We've all encountered
>> the problem in many language runtimes where reading a number using the
>> "friendly way" leaves the input in a state that requires fixing or yields
>> surprises for the next operation.
>>
>> This is because reading a number from an input stream is not any sort of
>> primitive; it is the composite of reading from the input, deciding what to
>> skip, deciding when to stop reading, converting to another type, deciding what
>> state to leave the input stream in, and deciding what to do if no number could
>> be found (or if the number was too big to fit into an int, etc.) This is not^3
>> simple!
>>
>> C starts with a simple and principled answer, which is that the IO primitive is
>> getchar() and putchar(). Reading or writing one character is unquestionably a
>> primitive. (But also, unless you are writing `cat`, no one wants to program
>> with getchar and putchar, because it's too primitive.)
>>
>> One can make a reasonable case for "write a line / read a line" being sensible
>> primitives. They are simple enough: no parsing, no deciding what to throw
>> away, no possible errors other than EOF, it is clear what state you leave the
>> stream in. These may not be what the student wants, but they are primitives a
>> student can deal with without having to understand parsing and error handling
>> and statefulness yet.
>>
>> String s = getALine();
>> printALine(s);
>>
>> is a program every student can reason about.
>>
>> But, it is true that dealing in strings, while honest and simple, is not always
>> what the student wants. But herein lies the strongest argument for not trying
>> to reinvent Scanner here: the ability to read numbers makes the complexity of
>> the problem, and hence of the API, much much bigger. (Scanner was very well
>> intentioned, and was not written by children, and yet none of us want to use
>> it. That's a sign that a one-size-fits-all magic input processing system is
>> harder than it looks, and for something that is explicitly aimed at beginners,
>> is a double warning sign.)
>>
>> I could imagine someone suggesting "why don't you just add `readLineAsInt`".
>> But what would happen next? Well, there would be a million requests
>> (including from folks like Cay) of "you should add X", and then the result is a
>> mishmash jumble of an API (that's already terrible), but worse, it's an onramp
>> that leads to nowhere. Once the user's needs are slightly more complicated,
>> they are nowhere.
>>
>> Remi has it absolutely right (yes, I really said that) with
>>
>>> The classical program is:
>>> input -> strings -> objects -> strings -> output
>>
>> We do not do users a favor by blurring the distinction between "input -> string"
>> and "string -> object", and because the latter is so much more open-ended than
>> the former, the latter infects the former with its complexity if we try.
>>
>> Is this simple API the most wonderful, be-all of APIs? Of course not. But it
>> is a sensible set of primitives that users can understand and *build on* in a
>> transparent way.
>>
>> Some teachers may immediately reach for teaching Integer::parseInt; that's a
>> reasonable strategy, it exposes students to the questions of "what happens when
>> preconditions fail", and the two compose just fine. But maybe you don't like
>> Integer::parseInt for some reason. Another way to teach this is to have them
>> write it themselves. This will expose them to all sorts of interesting
>> questions (what about whitespace? what about double negatives?), but of course
>> is also throwing in the deep end of the pool. But SimpleIO::readMeALinePlease
>> is agnostic; it works with both approaches.
>>
>> Could the JDK use some better tools for parsing? Sure; pattern matching has a
>> role to play here, a `String::unformat` would be really cool, and I love parser
>> combinators. All of this can happen in the future, and none have the effect of
>> making this API look like yet another white elephant like Scanner. Because it
>> focused purely on the basics.
>>
>>
>> On 2/19/2024 7:25 AM, Remi Forax wrote:
>>> I agree with Brian here,
>>> as a teacher, you have to talk about parsing and formatting, those should not be
>>> hidden.
>>>
>>> The classical program is:
>>> input -> strings -> objects -> strings -> output
>>>
>>> Rémi
>>>
>>> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>>>
>>> *From: *"Tagir Valeev" <amaembo at gmail.com>
>>> *To: *"Cay Horstmann" <cay at horstmann.com>
>>> *Cc: *"Brian Goetz" <brian.goetz at oracle.com>, "amber-dev"
>>> <amber-dev at openjdk.org>
>>> *Sent: *Monday, February 19, 2024 10:09:35 AM
>>> *Subject: *Re: SimpleIO in JEP draft 8323335
>>>
>>> I agree that simple methods to get numeric input are essential for beginners.
>>> They should not be distracted with a complex ceremony. Instead, they should be
>>> able to learn control flow statements and simple algorithms as soon as
>>> possible, having a simple way to get numbers from the user.
>>> With best regards,
>>> Tagir Valeev.
>>>
>>> On Mon, Feb 19, 2024 at 9:10 AM Cay Horstmann <cay at horstmann.com> wrote:
>>>
>>> Yes, that's what I am saying. If scanners live in vain, stick with a subset of
>>> the Console methods. Use its readLine. Make it so that SimpleIO uses
>>> System.console(). And add print and println to Console.
>>>
>>> The JEP talks about being able to start programming without having to know about
>>> static methods. How does a beginner read a number? With
>>> Integer.parseInt(readLine(prompt))?
>>>
>>> What about locales? Is print/println localized? Console.printf is. If so, how
>>> are beginners from around the world supposed to read localized numbers? With
>>> NumberFormat.getInstance().parse(readLine(prompt))?
>>>
>>> Adding localized readInt/readDouble to SimpleIO might do the trick. Do they
>>> consume the trailing newline? (The equivalent Scanner methods don't, which is
>>> definitely a sharp edge for beginners.)
>>>
>>> On 18/02/2024 23.08, Brian Goetz wrote:
>>> > OK, so is this really just that that you are bikeshedding the name? Renaming
>>> > `input` to `readLine`?
>>> >
>>> > This is a perfectly reasonable naming choice, of course, but also, not what you
>>> > suggested the first time around:
>>> >
>>> > > ... "a third API" ...
>>> >
>>> > > ... "there are two feasible directions" ...
>>> >
>>> > So what exactly are you suggesting?
>>> >
>>> >
>>> >
>>> > On 2/18/2024 5:03 PM, Cay Horstmann wrote:
>>> >> Like I said, either the scanner methods or the console methods are fine.
>>> >>
>>> >> I am of course aware of the utility/complexity of Scanner, and can understand
>>> >> the motivation to have a simpler/feebler behavior in SimpleIO. Like the one in
>>> >> Console.
>>> >>
>>> >> You don't have to "get a console". A SimpleIO.readLine method can just invoke
>>> >> readLine on the system console.
>>> >>
>>> >> My objection is to add yet another "input" method into the mix. "input" is weak.
>>> >> Does it read a token or the entire line? Does it consume the newline? And if it
>>> >> does just what readLine does, why another method name? Because "input" is three
>>> >> characters fewer? Let's not count characters.
>>> >>
>>> >> On 18/02/2024 22.43, Brian Goetz wrote:
>>> >>> I think you are counting characters and not counting concepts.
>>> >>>
>>> >>> Scanner has a ton of complexity in it that can easily trip up beginners. The
>>> >>> main sin (though there are others) is that input and parsing are complected
>>> >>> (e.g., nextInt), which only causes more problems (e.g., end of line issues.)
>>> >>> Reading from the console is clearly a () -> String operation. The input()
>>> >>> method does one thing, which is get a line of text. That's simple.
>>> >>>
>>> >>> Integer.parseInt (or, soon, patterns that match against string and bind an int)
>>> >>> also does one thing: convert a string from int. It may seem verbose to have to
>>> >>> do both explicitly, but it allows each of these operations to be simple, and it
>>> >>> is perfectly obvious what is going on. On the other hand, Scanner is a world of
>>> >>> complexity on its own.
>>> >>>
>>> >>> Console::readLine is nice, but first you have to get a Console. ("Why can I
>>> >>> print something without having to get some magic helper object, but I can't do
>>> >>> the same for reading?") What we're optimizing for here is conceptual
>>> >>> simplicity; the simplest possible input method is the inverse of println. The
>>> >>> fact that input has to be validated is a fact of life; we can treat validation
>>> >>> separately from IO (and we should), and it gets simpler when you do.
>>> >>>
>>> >>> On 2/18/2024 4:12 PM, Cay Horstmann wrote:
>>> >>>> I would like to comment on the simplicity of https://openjdk.org/jeps/8323335
>>> >>>> for beginning students.
>>> >>>>
>>> >>>> I am the author of college texts for introductory programming. Like other
>>> >>>> authors, I introduce the Scanner class (and not Console) for reading user
>>> >>>> input. Given that students already know about System.out, it is simpler to call
>>> >>>>
>>> >>>> System.out.print("How old are you? ");
>>> >>>> int x = in.nextInt(); // in is a Scanner
>>> >>>>
>>> >>>> than
>>> >>>>
>>> >>>> int x = Integer.parseInt(console.readLine("How old are you? "));
>>> >>>>
>>> >>>> or with the JEP draft:
>>> >>>>
>>> >>>> int x = Integer.parseInt(input("How old are you? "));
>>> >>>>
>>> >>>> Then again, having a prompt string is nice too, so I could imagine using the
>>> >>>> Console API with Integer.parseInt and Double.parseDouble, instead of
>>> >>>> Scanner.nextInt/nextDouble.
>>> >>>>
>>> >>>> But why have a third API, i.e. "input"?
>>> >>>>
>>> >>>> I think there are two feasible directions. Either embrace the Scanner API and
>>> >>>> next/nextInt/nextDouble/nextLine, or the Console API and readLine. Adding
>>> >>>> "input" into the mix is just clutter, and ambiguous clutter at that. At least
>>> >>>> readLine makes it clear that the entire line is consumed.
>>> >>>>
>>> >>>> Cheers,
>>> >>>>
>>> >>>> Cay
>>> >>>>
>>> >>>> --
>>> >>>>
>>> >>>> Cay S. Horstmann |
>>> >>>> https://urldefense.com/v3/__http://horstmann.com__;!!ACWV5N9M2RV99hQ!IuXZk_tqIH8rEw1bD3uYb8UcIZF-nnoeFT3UG17pMO5EVXIYVRaAKi7XCq_T02HwnAek1wuV8Wed08w$
>>> >>>> | mailto:cay at horstmann.com
>>> >>>
>>> >>
>>> >
>>>
>>> --
>>>
>>> --
>>>
>>> Cay S. Horstmann | http://horstmann.com
>>> <https://urldefense.com/v3/__http://horstmann.com__;!!ACWV5N9M2RV99hQ!IZrLgaQxOHBjUURoC5mWbfsijev257bb4C0DMamUDpoGqS5JMACpaMKsbUNQlWcGds7fifmS9sARC6aKMHEf$>
>>> | mailto:cay at horstmann.com
>>>
>>>
>>
>
> --
>
> --
>
> Cay S. Horstmann | http://horstmann.com | mailto:cay at horstmann.com
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