Standard definitions of terms within specifications

Question

Quite often I find that I am repeating myself when creating a challenge. For example, usually I have to retype the definition of "random" in all of my posts, or I have to specify the same thing about how reasonable input and output can be provided in every challenge.

This post is meant to be a collection of "standard" definitions that may be assumed in every question, and do not need to be specified within the challenge. Definitions will apply once the post with the defintion has a score of +5 or more, and it has at least twice as many upvotes as downvotes.

Answer 1

"random"

The term "random" means that you may:

1. Use your language's built-in random number generator,
2. Use /dev/random, or
3. Create a RNG that is equivalent to a standard RNG (such as the Mersenne Twister).

Answer 2

"uniformly random"

There are two distinct things to define for "uniform" (in the context of uniformly distributed random variables).

1. If "uniform" is not specified, then "random" does not imply uniformly random.
2. If "uniform" is specified, the standard PRNG (pseudo random number generator) of your programming language can be assumed uniform.

Examples

• Output a random integer from 1 to 5:
  It does not matter if 2 is output with higher probability than 3.
• Output a uniformly random integer from 1 to 5:
  The probability of each of 1, 2, 3, 4, and 5 must be 0.2, but a slight deviation from this due to the implementation of random is fine (provided that the implementation is not of a different distribution - you can't use a normal distribution to save bytes).
• Output a uniformly random point on a disk:
  Choosing random cartesian coordinates (x,y) and rejecting if outside the disk is fine.
  Choosing random polar coordinates (r, theta) is not acceptable even though r and theta can be assumed uniform, because the distribution in 2D is no longer uniform (even with perfectly uniform r and theta).

If a challenge specifies statistical tests as part of the validity criteria, then that overrides these allowances.

Answer 3

"input" and "output"

Refer to Default for Code Golf: Input/Output methods. The list includes, but not is limited to:

• STDIN/STDOUT
• function argument/return value
• command line arguments/program exit code
• reading from/writing to a file
• dialog boxes
• popping from/pushing to the stack (for stack-based languages like GolfScript; this is essentially the equivalent of a function's arguments/return values for those languages)

Answer 4

"Black-Box-Functions"

The content (i.e. the code) of black-box-functions may not be accessed, you can only call them (passing arguments if applicable) and observe their output.

They should also have no side effects, except for e.g. accessing RNGs or time, but no communication with the rest of the program should take place other than through the input arguments and the output.

This term is used in the list of default IOs in a number of suggestions. (1),(2),(3)

Answer 5

"Positive", "Negative", "Non-Negative", "Non-Positive"

Positive, by default, means strictly positive, ie. all N larger than zero. Zero is not a positive number.

Negative means all N less than zero. Zero is not a negative number.

Non-negative means all N larger than or equal to zero. Zero is a non-negative number.

Non-Positive means all N smaller than or equal to zero. Zero is a non-positive number.

Answer 6

Universally testable answers

An answer will be considered to be universally testable if:

1. It is written in a programming language which has a compiler/interpreter available on Windows, Linux & Mac where said compiler/interpreter can be downloaded from the web free of charge (not including free trials) and does not require sign up/registration.
2. or it is written in a programming language that has an online compiler/interpreter such as http://ideone.com/, which is available free of charge and does not require sign up/registration, where the answer may be fully tested within the online compiler/interpreter i.e. doesn't need access to local resources.

Additionally, if the behaviour of the answer is different on different platforms/architectures, it should still meet the question criteria on all platforms/architectures.

Answer 7

Write a function

I propose this as the default for code golf questions that as for a function rather than a full program. I'm sorry if this all seems overly pedantic, but I've seen every single one of these points come up in actual questions and answers, and I'd like to have comprehensive rulings on them available.

I must admit I have a limited knowledge of languages, especially esoteric ones, so I welcome suggestions to make this more accessible to a wide class of languages.

Specification

1) The code must result in a named function (or analogous execution unit in your language) that fits the specifications.

2) The function, when called by name on its inputs, must evaluate to the desired outputs.

3) There can be code outside the function definition, whose characters are also counted.

4) Calling the function multiple times must produce the right answer each time.

5) Optional additional parameters are acceptable; mandatory additional parameters are not.

Explanations

The spec is meant to capture the idea that a function, once created, should be usable to transform inputs to outputs in the fashion asked for.

1) The code must result in a named function (or analogous execution unit in your language) that fits the specifications.

While in C-style languages, the function is usually created by a function definition, this allows for other methods such as a lambda-expression like f=lambda x:x*x or a composition f=compose(g,h) or a decoration f=memoize(f) as long as the result is saved to a variable.

2) The function, when called by name on its inputs, must evaluate to the desired outputs.

This captures the requirement that the function be a function. Its inputs should be passed in, rather than taken through STDIN or taken from a global valuable. Its value must be returned, rather than saved to a variable or printed. To be clear, this does not mean an invocation of the function by included in the code, but that the function must behave as desired in invoked.

3) There can be code outside the function definition, whose characters are also counted.

This rule is an assurance that even if asked for a function, your code doesn't entirely have to do that function. Programs might make imports, saved global variable, and define auxiliary functions outside that function.

4) Calling the function multiple times must produce the right answer each time.

In other words, it's not acceptable to have your function only work the first time. Subsequent calls within a single run should also work according to the spec. This could come up if the function modifies a global value.

This does not preclude the function modifying the value it was passed in. So, the function f should print the same output twice on print f(1,2); print f(1,2) but not necessarily l=[1,2]; print f(l); print f(l).

Here's an answer where this question can up in practice, with Falko's suggestion to save a character by defining the initial list as an optional parameter def f(a,b=[0]*1000): causes it to be overwritten for subsequent runs.

5) Optional additional parameters are acceptable; mandatory additional parameters are not.

In other words, if asked for a function that takes two numbers, it's fine to have one that takes two numbers and an optional third number, as long as it behaves as asked when given only two numbers. The reasoning is that this would pass any test according to the specs, so it can behave arbitrarily in the non-spec case of three numbers. However, having a mandatory additional parameter and saying "call f as f(a,b,0) does not fit the spec.

An optional additional parameter might be useful for golf to define a recursive function or to save a method name to a variable before the function body.

Things not addressed

Input/outputs formats: If asked for a function that takes no numbers, can yours instead take a list/array/tuple of two numbers? Can you output a float if asked for a whole number?

Fallbacks: What should a language that does have functions do? I think this should be addressed with a general convention of "Do the closest you can, but only if what was required was impossible in the language.

Answer 8

"N random X"

Where N denotes a natural number and X denotes (members of) a set with finite cardinality.

The standard definition for "N random X" is "N independent identically distributed uniform (pseudo-) random samples from the space of all X".

As a concrete case "generate 3 random printable ASCII characters" could be satisfied by [1,2,3].map(_=>String.fromCharCode(Math.random()*95+32)) in JavaScript (ES6).