Default for Code Golf: Input/Output methods

Question

It looks like we have a consensus that we want certain defaults for the format which answers are expected in for code-golf. On that poll, the question arose twice, which input/output formats should be allowed for programs and functions.

So here is another poll. This one works different though. All the input/output methods are independent of each other, so there will be one answer per method. Upvote all you think are reasonable for the default. Downvote those which you think shouldn't be allowed unless the OP explicitly permits them.

To keep this remotely manageable, I have not posted individual answers for all possible inputs for functions. So there are only four: functions can take input/output via their arguments and return values. Or functions can use any method full programs can. I don't think there is any point in (say) allowing programs to take input from STDIN (only) and to allow functions to take input from ARGV (only) or something like that. If you disagree, please leave a comment.

If I've overlooked an I/O method, feel free to add your own answer.

Note: Some votes have been reverted because they were detected as serial voting. If you vote on multiple answers, please leave some time between votes.

A method is allowed if it has 5 net votes and at least twice as many upvotes as downvotes.

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Answer 1

Assembly programs may read input from some specified memory location

If there are no I/O devices available, an answer might consist of a subroutine that reads its input values from some specified memory location (e.g. read a zero-terminated string starting at $0000).

Answer 2

Multiple arguments to a function can be taken as a list or tuple instead

For example, if you needed to take in two integers as arguments, you can take one argument: a list of both integers.

Apparently, this isn't already here, so I'm posting this answer.

Answer 3

Full programs may take array/string input (of unknown length) via stdin in the form of <length> <contents> or <contents> <sentinel>

EOF handling is a common problem in many languages, not just esolangs. But only "regular" languages that support proper arrays and functions can circumvent this issue by writing functions instead of full programs.

Most programming contest problems (which only support stdin/stdout as I/O) solve this issue by giving extra information in the standard input in one of the two ways:

• give "how many items you need to expect in the input" in the standard input itself, before the start of the actual content, or
• give a special value at the end of input so that you can "terminate the program when this value is entered".

I believe these solutions are also a natural extension of

• An array may be represented in input as a pointer and length and
• An array may be represented as a buffer terminated with a sentinel value

to full programs respectively, which currently only apply to functions.

The same condition for the sentinel value applies when the sentinel value method is used:

It should be noted that the sentinel value must be the one that is guaranteed to not appear in any valid input [...], since their presence breaks the premise of the I/O method.

Answer 4

Functions may return their result in an optional type wrapper

Relevant meta discussion.

By "optional type wrapper" I mean something like Maybe a in Haskell, Option<T> in Rust, etc.

The consensus was that this should be allowed because it functions like a singleton wrapper, or like a possibly-erroring function that never actually errors.

Answer 5

I/O for sequence questions may either be 0-indexed or 1-indexed

Any sequence question that has the user output the \$n\$th term, first \$n\$ terms, etc. of a sequence should allow programs to index the first element of the sequence as 0 or 1 at the answerer's choice, as long as the program is consistent.

Answer 6

An array may be represented in input as a pointer and length.

For example in C you could use:

int f(int*p,int l){...}

Answer 7

Assembly programs may write output to registers

If there are no I/O devices available, an answer might consist of a subroutine that leaves its computed output values in the machine registers upon returning.

Answer 8

Regexes may output via the list of matched strings (the captured group 0)

Answer 9

CGI scripts may take input via GET/POST parameters

A CGI script required to take, e.g., three inputs can be expected to be called as the GET request

GET script.cgi?<A>=<1st input>&<B>=<2nd input>&<C>=<3rd input> HTTP/1.1

(where A, B and C are keys of the poster's choice) of the equivalent POST request.

Answer 10

black-box functions to be taken as input can be passed as an argument

This holds for functional languages or languanges that do have first class functions/anonymous functions/lambda functions or function pointers, for instance: Java, JavaScript, C++, TI-Basic, Python, Octave, Matlab, Haskell, Lisp

Answer 11

You may assume that the input is valid

When parsing an input, you may assume that the input is already valid. You are not required to validate it unless the challenge is specifically about testing whether the input is valid or not.

Answer 12

Functions may return a function that returns the result

This is very similar to currying, the only difference being that only the first call includes an argument. Sometimes it's useful to curry a recursive function that has only one argument, especially if that argument doesn't need to be modified to find the result. For example, each of these JavaScript functions returns the bit-length of a positive integer:

f=(n,x)=>n?f(n>>1,-~x):x
f=(n,x)=>n>>x?f(n,-~x):x
n=>f=x=>n>>x?f(-~x):x

All three functions can be called by assigning them to g and calling them with e.g. g(49); however, the third version must be called again with g(49)() to actually return the result. Again, this is very similar to currying, where the arguments are passed separately (g(a)(b) rather than g(a,b)).

Note that no additional input should be needed to get the result (i.e. "to call on a number x, use f(x)(2)"). Optional arguments are fine, of course (x=>(y=2)=>x+y).

There is also a meta post about this here, though it was closed as a duplicate of this question.

Answer 13

Programs may take input from a file

Answer 14

Programs and functions may return a boolean value via the presence or absence of output

Answer 15

When a challenge asks for an array as input/output, you may use a list instead, and vice-versa

Note that some languages may lack one of these concepts. For example, TI-Basic does not have an array datatype (but has lists) and C does not have a list in its standard library, but has arrays as part of the language.

In keeping with the general flexibility of I/O formats, I suggest we allow to use them interchangeably for all languages.

Answer 16

Lists of decimal digits and strings that match ^[0-9]*$ are interchangeable...

...but not when this may make the input format inconsistent.

For example, let's say you can assume the string input will match ^[1457]+$, which is a subset of ^[0-9]*$. Then, '1775' can also be input as [1, 7, 7, 5].

However, for a counterexample, let's assume the string input will match ^[a0-8]{2,15}$, which isn't a subset of ^[0-9]*$. In this case, no, you may not use a list of digits, since you can't use one to represent 1aa7708, for example. You can use [1, 1, 8, 8, 6, 4] to represent 118864, but this inconsistency is invalid by default.

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I posted this after having come across numerous occurrences where I've had to ask about this in the comment section of the question, so I thought "why not post this here?". Surprisingly, this, AFAICT, hasn't ever been posted yet! I definitely have a positive opinion.

Answer 17

Functions may return a promise containing the output

About Promises

• Wikipedia article on futures & promises
• MDN article on the JavaScript Promise object

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Example

Consider the following function to retrieve my rep from the API, with the output logged from the last Promise in the chain:

f=

_=>fetch("//api.stackexchange.com/users/58974?site=codegolf").then(r=>r.json()).then(j=>console.log(j.items[0].reputation))

f()

I propose instead that we simply be allowed to return the Promise containing the output, like so:

f=

_=>fetch("//api.stackexchange.com/users/58974?site=codegolf").then(r=>r.json()).then(j=>j.items[0].reputation)

f().then(console.log)

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Conditions of Use

This section requires more detail, please edit it to include any other conditions you think should be covered or to add tags to the existing conditions.

code-golf

In challenges that use code length as a measure for the winning criterion, returning a promise would not be permitted if further manipulation would be required to achieve the desired output, as in this example:

f=

_=>fetch("//api.stackexchange.com/users/58974?site=codegolf").then(r=>r.json()).then(j=>j.items[0])

f().then(i=>console.log(i.reputation))

fastest-code

If this method is used in time-based challenges then the time required to resolve the final promise must be counted towards your score.

Answer 18

black-box functions to be taken as input can be assumed to be predefined under a given name

This holds for languages that do have classical functions, for instance: Java, JavaScript, VB, C, C++, TI-Basic (some versions), Python, Octave, Matlab, Haskell, Lisp

This proposition is the opposite of that one which only allows this method of taking input for languages that cannot take functions as arguments.

Answer 19

Metaprogramming languages may return a boolean by compiling/not compiling

For example, C++ template metaprogramming has no "return value". A common way for a C++ template metaprogramming to reject something is to fail to compile (sometimes in a SFINAE way, sometimes not).

Answer 20

Regexes may output via any captured groups

Users can specify which subset of captured group(s) contains the output; it doesn't have to be just group 0.

Answer 21

Strings, arrays of characters, and arrays of bytes are interchangeable

Surprised this isn't here yet.

Languages like C don't really have strings, and arrays of bytes (*char) is already the common way of representing them. C++ does have strings but most CGSE answers still seem to prefer pointers to arrays of bytes.

Other languages like Rust have strings that are really inconvenient to work with, so I've already been using [u8] and Vec<u8> most of the time.

Answers may in some cases prefer using string tools on arrays, as long as the array will never have values over 255 taking input as a string then using functions like .replace() and .split() would be valid.

Or some languages, like regex, have only strings and would make some number challenges very inconvenient without using char values.

Actually this is already the default as stated here but I think including it here is still valuable since this post is a lot easier to find.

Answer 22

Regexes may output a number via the number of matches

Or truthy / falsey as whether they match.

Answer 23

An array may be represented in input as a begin pointer and an end pointer.

like what's done in C++ std

Answer 24

Programs may write output to the clipboard

Complementing the programs may take input from the clipboard proposal.

Answer 25

A multidimensional rectangular array may be represented by the list [dimensions, flattened array]

Answer 26

Floating point numbers may be represented as fractions.

For example, instead of literal 0.5 or "0.5", the program can return "1/2" or [1,2]. It's especially useful for languages without out-of-the-box floating point support.

Answer 27

Spreadsheet languages can take input from a specific cell / group of cells

Most Excel / Google Sheets answers seem to do this anyway, I don't know why it wasn't here.

For example, this answer takes input through the A1 cell of a spreadsheet and performs operations on that to arrive at the final output.

Answer 28

A function can output by modifying a global variable if that variable is automatically outputted/displayed

It has been decided that in general, functions may not output by just modifying a global variable because that would make it too much like a snippet, which is not allowed.

But what about languages where the value of that global variable is automatically outputted? For example, say there is a language where output is stored in an output string variable, and automatically displayed when the program finishes execution.

For example, in Scratch, the current ruling is that output must be displayed via the say block. However, in Scratch variables are shown automatically if not unchecked in the interface, just as say shows output automatically if the sprite is not checked as hidden in the interface. These should be allowed interchangeably since both output a value without any extra code at the call site.

Answer 29

Programs may output using their return value

Iff it is legit regarding their specs and compilers.

Certain language treat programs as function, allowing programs to communicate via returns. Hence, we shoule allow such programs to be considered as whole, and not as snippet.

Answer 30

Programs may take input as arguments to command line flags

If a language has a command line flag in the form --flag=arg, input may be taken as the argument to that flag. For example:

./language -f --option=2 <prog>

Can be run for the input 2.