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.

At the end of the week, I will amend the code-golf tag wiki, allowing all methods by default which have 5 net votes and at least twice as many upvotes as downvotes. I will try to keep an eye on this in the future, to amend the defaults if the polls change.

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.

Update

The current results of the polls are now part of the tag wiki. Please notify me, if results change significantly and the wiki should be amended.

Martin Büttner · Answer 1 · 2014-11-02 23:13:50Z

up vote 57 down vote

Functions may output via their return value(s)

answered Nov 2 '14 at 23:13

community wiki

Martin Büttner

1

This has my upvote. – Martin Büttner♦ Nov 2 '14 at 23:15

10

@hosch250 Wait, are there languages that have functions without return values? o.O – Martin Büttner♦ Nov 3 '14 at 0:17

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Martin Büttner · Answer 2 · 2014-11-02 23:01:03Z

up vote 50 down vote

Programs may take input via STDIN

answered Nov 2 '14 at 23:01

community wiki

Martin Büttner

1

This has my upvote. – Martin Büttner♦ Nov 2 '14 at 23:09

4

Should I downvote this? – Bojidar Marinov Nov 16 '15 at 20:24

add a comment |

Martin Büttner · Answer 3 · 2014-11-02 23:04:20Z

up vote 47 down vote

Programs may output to STDOUT

answered Nov 2 '14 at 23:04

community wiki

Martin Büttner

1

This has my upvote. – Martin Büttner♦ Nov 2 '14 at 23:12

2

did you have to do this to every single one you voted up? – TheDoctor Nov 4 '14 at 23:25

5

@TheDoctor I can't actually vote, because I posted the answers myself, so those comments are my votes. – Martin Büttner♦ Nov 4 '14 at 23:28

1

Ah that makes sense – TheDoctor Nov 4 '14 at 23:38

add a comment |

Martin Büttner · Answer 4 · 2014-11-02 23:10:53Z

up vote 44 down vote

Functions may take input via function arguments

answered Nov 2 '14 at 23:10

community wiki

Martin Büttner

1

This has my upvote. – Martin Büttner♦ Nov 2 '14 at 23:12

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2 revs · Answer 5 · 2014-11-03 00:22:08Z

up vote 43 down vote

Programs may take input via GUI prompts

(This is for languages, for which this is the closest alternative to STDIN, like JavaScript's prompt(), Mathematica's Input[] or InputString[] and Matlab's input().)

edited Nov 3 '14 at 0:22

community wiki

2 revs
Martin Büttner

1

This has my upvote. – Martin Büttner♦ Nov 3 '14 at 0:11

1

What about for other languages? – Ypnypn Nov 4 '14 at 0:32

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Martin Büttner · Answer 6 · 2014-11-02 23:03:02Z

up vote 35 down vote

Programs may take input via command-line arguments

answered Nov 2 '14 at 23:03

community wiki

Martin Büttner

1

This has my upvote. – Martin Büttner♦ Nov 2 '14 at 23:11

add a comment |

ryvnf · Answer 7 · 2015-10-07 19:16:25Z

Programs may output by displaying it on screen.

This makes it possible to use languages like Vim script that can't print output directly to stdout.

Example from this challenge:

$ echo "This is a test line!" | vim - -c 'nm Q vEUWvEuWQ|norm Q'

Will display:

THIS is A test LINE!
~
~
~
~
~

Within a Vim session.

I think that this way of displaying the result should be valid. I am sure that there are other domain specific languages like Vim script that lacks full I/O support and could use another way to display the result.

Martin Büttner · Answer 8 · 2014-11-02 23:15:16Z

up vote 25 down vote

Functions may output via the same methods as full programs

(This depends on how the poll goes, but could be any subset of STDOUT, STDERR and file.)

answered Nov 2 '14 at 23:15

community wiki

Martin Büttner

1

@JanDvorak One simple golf use is that print is shorter than return in Python. – xnor Nov 3 '14 at 8:57

1

Eugh. Not a fan of that optimisation. What it could be useful for is printing in a loop rather than collecting results in an array. Still not a fan of allowing that. – Jan Dvorak Nov 3 '14 at 9:02

8

@xnor Why not, full programs are allowed to do that, too, right? – Martin Büttner♦ Nov 3 '14 at 11:22

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2 revs · Answer 9 · 2016-02-19 10:52:51Z

Functions may take multiple arguments via currying

For some functional programming languages like Haskell this is actually necessary, because only single-argument functions exist and functions with multiple arguments are (somewhat transparently) implemented as curried functions. (The alternative would be to take a list or tuple of the values, but that is not how one would naturally write a two-argument function in Haskell.)

As per this consensus the same should also be allowable for languages where multi-argument functions do exist. As an example from JavaScript, instead of defining

f=(a,b)=>...

and calling it like f(a,b) one could then also define

f=a=>b=>...

and call it like f(a)(b).

@ChristianIrwan True (if that is even allowed) - I clarified that part a bit. — Martin Büttner♦, Feb 19 at 10:53

Rainbolt · Answer 10 · 2015-05-28 13:56:25Z

Programs may output using their exit code...

... if and only if the challenge requires an integer as output, obviously.

Exit codes are basically a return value for programs. If functions can output using their return values, it makes sense that programs should be able to do the same.

Examples:

Martin Büttner · Answer 11 · 2014-11-02 23:12:22Z

up vote 18 down vote

Functions may take input via the same methods as full programs

(This depends on how the poll goes, but could be any subset of STDIN, ARGV and file.)

answered Nov 2 '14 at 23:12

community wiki

Martin Büttner

11

@JanDvorak I don't see the relevance of good coding practices for code golf. And some languages don't even have functions and they aren't necessarily at a disadvantage by allowing functions. The idea of being more liberal in the options for I/O is so that each language can pick what's really shortest. – Martin Büttner♦ Nov 3 '14 at 11:10

1

The only time that I would object to a function taking input in the same way as a program is if the question was phrased "Write a function that takes the following arguments". This poll applies to questions that are not in such a specific format, so I see no reason to exclude functions that read from stdin. – trichoplax Nov 4 '14 at 13:16

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Martin Büttner · Answer 12 · 2015-03-25 10:51:38Z

up vote 17 down vote

Functions may output by modifying their arguments or writing to out arguments

answered Mar 25 '15 at 10:51

community wiki

Martin Büttner

4

@ThomasKwa Yes, provided the changed value will then be accessible in the context that called the function. – Martin Büttner♦ Jun 10 '15 at 21:18

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2 revs · Answer 13 · 2015-06-11 01:01:53Z

up vote 17 down vote

Programs may combine two or more input methods

For example, if the inputs are a string and an int, a function that takes a string as an argument and an int from STDIN would be valid.

The input format must still be consistent for a given program.

edited Jun 11 '15 at 1:01

community wiki

2 revs
Thomas Kwa

add a comment |

Martin Büttner · Answer 14 · 2014-11-02 23:08:45Z

up vote 15 down vote

Programs may output to a file

answered Nov 2 '14 at 23:08

community wiki

Martin Büttner

1

This has my downvote. – Martin Büttner♦ Nov 7 '14 at 9:45

5

Why are people against this? – xnor Nov 8 '14 at 5:48

1

@xnor is /dev/null considered a valid output file? I might as well submit a blank program and claim it outputs the correct answer to /dev/null. – Patrick Roberts Feb 15 at 21:55

add a comment |

SuperJedi224 · Answer 15 · 2015-09-22 19:46:43Z

up vote 15 down vote

The contents of the tape post-execution may be used as a Turing machine's output

answered Sep 22 '15 at 19:46

SuperJedi224

6,429516

2

This has my upvote. – SuperJedi224 Sep 22 '15 at 20:54

add a comment |

SuperJedi224 · Answer 16 · 2015-09-22 19:49:48Z

up vote 12 down vote

Where applicable, Turing machines supporting multiple halt states may also output via their halt state

This is equivalent to programs outputting via their exit code.

answered Sep 22 '15 at 19:49

SuperJedi224

6,429516

1

This has my upvote. – SuperJedi224 Sep 22 '15 at 20:54

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SuperJedi224 · Answer 17 · 2015-09-22 19:45:25Z

up vote 11 down vote

Input for Turing machines may be written to the tape pre-execution

The read-write head should start on the leftmost cell of the portion of the tape containing the input.

answered Sep 22 '15 at 19:45

SuperJedi224

6,429516

1

This has my upvote. – SuperJedi224 Sep 22 '15 at 20:53

3

I think this should only be allowed if that's the only method of input. – mbomb007 Oct 8 '15 at 20:39

1

For standard turing machines, it is. – SuperJedi224 Oct 8 '15 at 20:59

add a comment |

jimmy23013 · Answer 18 · 2015-05-30 03:52:04Z

up vote 10 down vote

SQLs may take input from a named table

which is probably not good enough. But I don't know a better way.

answered May 30 '15 at 3:52

jimmy23013

16.8k917

add a comment |

VTCAKAVSMoACE · Answer 19 · 2016-02-19 13:28:13Z

up vote 9 down vote

Input for stack-based language's functions may be pushed to the stack before calling

Stack-based languages may assume that the input for their function is automatically pushed to the stack.

answered Feb 19 at 13:28

VTCAKAVSMoACE

5,558931

1

+1, this is the de facto standard for CJam and GolfScript (and probably some other stack-based languages). You might want to make a corresponding answer for output. – Martin Büttner♦ Feb 19 at 13:29

1

I think the emphasis here needs to be on "function", as opposed to snippet. There's a very fine line between the two... – Sp3000 Feb 19 at 13:34

add a comment |

Martin Büttner · Answer 20 · 2014-11-02 23:07:19Z

up vote 7 down vote

Programs may take input from a file

answered Nov 2 '14 at 23:07

community wiki

Martin Büttner

5

... only if makes sense for the challenge, and even then you should input a file name first... I'd say – Jan Dvorak Nov 3 '14 at 6:32

2

@JanDvorak That's a "no", because that makes the file name itself the input (which you would take from STDIN or ARGV). – Martin Büttner♦ Nov 3 '14 at 11:07

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Martin Büttner · Answer 21 · 2016-02-20 20:32:47Z

up vote 6 down vote

Functions in stack-based languages can leave the output on the stack

Mostly for completeness sake. This is the de-facto standard for CJam and GolfScript and probably other stack-based languages.

answered Feb 20 at 20:32

Martin Büttner♦

87.4k194186

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jimmy23013 · Answer 22 · 2015-05-30 03:44:42Z

up vote 5 down vote

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

answered May 30 '15 at 3:44

jimmy23013

16.8k917

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Dennis · Answer 23 · 2015-11-27 16:35:24Z

up vote 5 down vote

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.

answered Nov 27 '15 at 16:35

community wiki

Dennis

1

@jimmy23013 PHP4.1: <?eval($c); (assuming short_tags and register_globals, the code can be anywhere, even in a cookie (if below 4kb)). Or even <?eval(fgets(STDIN)). Or, for Javascript, eval(prompt()). Or eval "$s" for bash. Other languages have the same problem. Any language that allows evaluation of a string containing code has the same problem – Ismael Miguel Nov 27 '15 at 20:19

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Lynn · Answer 24 · 2016-02-20 22:33:07Z

up vote 5 down vote

Assembly programs may take input from registers

If there are no I/O devices available, an answer might consist of a subroutine that reads its input values from the machine registers.

answered Feb 20 at 22:33

Lynn

14k96

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Lynn · Answer 25 · 2016-02-20 22:34:37Z

up vote 5 down vote

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.

answered Feb 20 at 22:34

Lynn

14k96

add a comment |

Lynn · Answer 26 · 2016-02-20 22:36:59Z

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).

Lynn · Answer 27 · 2016-02-20 22:39:02Z

Assembly programs may write output to some specified memory location

If there are no I/O devices available, an answer might consist of a subroutine that writes its output values to some specified memory location (e.g. write a machine word to $0000).

jimmy23013 · Answer 28 · 2015-05-30 03:42:14Z

up vote 3 down vote

Regexes may output a number via the number of matches

Or truthy / falsey as whether they match.

answered May 30 '15 at 3:42

jimmy23013

16.8k917

6

Plain regex submissions are still not generally accepted as valid so I'm not sure it's worth adding defaults for this very specific case that a lot of people don't accept at all. – Martin Büttner♦ May 30 '15 at 10:27

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jimmy23013 · Answer 29 · 2015-05-30 03:46:57Z

up vote 3 down vote

Regexes may output via any captured groups

The users can specify which captured group(s) contain the output, not necessarily group 0.

answered May 30 '15 at 3:46

jimmy23013

16.8k917

add a comment |

lirtosiast · Answer 30 · 2016-03-15 17:16:09Z

up vote 2 down vote

Programs may take input as the value of the last expression

Using something like TI-84 BASIC's Ans, which is a variable that stores the value of the last expression. This the shortest way for TI-BASIC to take input, but its validity was recently questioned. To be clear, this is how the process works with Ans:

Within a program, type the input (number, list, string, etc.), followed by a newline to separate statements, followed by the program name, then press Enter. For example,
```
1337
prgmFACTOR
```
Outside a program, type the input, press Enter, then type the program name and press Enter.

edited Mar 15 at 17:16

lirtosiast

14.7k920

answered Feb 25 at 22:52

NinjaBearMonkey

6,563213

3

I think by definition that submission would not be a full program but a snippet that requires some sort of REPL environment which are disallowed by default. – Martin Büttner♦ Feb 25 at 22:53

2

I think that TI-BASIC is a special case, it being fundamentally different from other languages, and only being callable from what can be considered a REPL; so what then is to differ a full program from a snippet? – Cᴏɴᴏʀ O'Bʀɪᴇɴ Feb 29 at 17:06

2

@CᴏɴᴏʀO'Bʀɪᴇɴ I disagree, you can write full programs in the REPL but you can also write them in separate "files" that can be executed. They even support arguments when the program is called, but can also read from stdin or via prompt. – flawr Mar 5 at 12:55

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Default for Code Golf: Input/Output methods

Update

36 Answers 36

Functions may output via their return value(s)

Programs may take input via STDIN

Programs may output to STDOUT

Functions may take input via function arguments

Programs may take input via GUI prompts

Programs may take input via command-line arguments

Programs may output by displaying it on screen.

Functions may output via the same methods as full programs

Functions may take multiple arguments via currying

Programs may output using their exit code...

Functions may take input via the same methods as full programs

Functions may output by modifying their arguments or writing to out arguments

Programs may combine two or more input methods

Programs may output to a file

The contents of the tape post-execution may be used as a Turing machine's output

Where applicable, Turing machines supporting multiple halt states may also output via their halt state

Input for Turing machines may be written to the tape pre-execution

SQLs may take input from a named table

Input for stack-based language's functions may be pushed to the stack before calling

Programs may take input from a file

Functions in stack-based languages can leave the output on the stack

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

CGI scripts may take input via GET/POST parameters

Assembly programs may take input from registers

Assembly programs may write output to registers

Assembly programs may read input from some specified memory location

Assembly programs may write output to some specified memory location

Regexes may output a number via the number of matches

Regexes may output via any captured groups

Programs may take input as the value of the last expression

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