Is it truthy or falsy?

Question

There are so many different ways to express whether something is true or not! The goal of this challenge is to produce a standardized output of truthy or falsy for various input truthy and falsy values.

For the purposes of this challenge, the following inputs are considered truthy:

1. A string representing a signed integer with a non-zero value (contains only the digits [0-9], with an optional - at the beginning). Note that the string -0 will never be given as input. A non-zero integer will never be preceded by a 0 (i.e. 01 will never be given as input, similarly -01 will never be gien as input).
2. The case-insensitive strings equivalent to one of defined, found, nonnil, non-nil, on, success, t, true, y, and yes

For the purposes of this challenge, the following inputs are considered falsy:

1. The string 0. Repeated zeros (00, 00...) will never be given as input.
2. An empty string
3. The case-insensitive strings equivalent to one of f, failure, false, n, nan, nil, no, notfound, not-found, null, nullptr, off, and undefined

Input

The input is a string representing a truthy/falsy value. The string may come from any source desired (stdio, function parameter, etc.). There is no leading/trailing whitespace.

The input is guaranteed to match one of the allowed truthy/falsy values above (i.e. you do not need to provide any error handling).

Output

Your program/function must output a truthy/falsy value which represents the "truthy-ness" or "falsy-ness" of the input. You are only allowed to specify exactly 1 truthy and 1 falsy value which your output must convert the input to (these are your "standardized" truthy/falsy value). The output may be written to any sink desired (stdio, return value, output parameter, etc.).

Please specify what truthy and falsy value you chose in your answer.

Ex.: If you choose the string true as a truthy value, you cannot also have the integer 1 for truthy.

Test Cases

Test cases are formatted as the first line is the input, and the second line is the output.

-1
true

1
true

1234
true

-4321
true

defined
true

deFined
true

Found
true

nonnil
true

non-nil
true

ON
true

SuCCess
true

T
true

true
true

y
true

YeS
true

0
false

'' (empty string)
false

faLSE
false

f
false

Failure
false

n
false

NaN
false

nil
false

no
false

notfound
false

not-Found
false

NULL
false

nullptr
false

OFF
false

unDefined
false

Scoring

This is code-golf; shortest code in bytes wins. Standard loopholes apply. You may use any built-ins desired.

Answer 1

MATL, 20 bytes

U|sG36ZA13\[BID1]m+g

Input is a string enclosed in single quotes. Output is 1 for truthy or 0 for falsy.

Try it online! Or verify all test cases.

How it works

U|s      % Take input implicitly. Interpret as number, absolute value, sum
G36ZA    % Push input again. Convert from base-36
13\      % Modulo 13
[BID1]   % Push array [6 3 8 1]
m        % True if member: gives 1 iff the result from modulo 13 is in the array
+g       % Add, convert to logical. Display implicitly

This performs two tests on the input:

1. Try to interpret the input as a number, and detect if it is nonzero. The function used to interpret a string as a number outputs an empty array if it's not possible; and the sum of the entries of an empty array is 0. So it suffices to try the conversion, take the absolute value, and sum. This gives a positive value if the input contains a nonzero number, and 0 otherwise.
2. Assuming the input string doesn't represent a number, we need to classify it into one of the two given sets. To do this, the input is interpreted as the digits of a number expressed in base-36, using alphabet '01...9ab...z'. The base conversion function is case-insensitive and ignores digits not present in the alphabet (in our case, '-'). It turns out that the modulo 13 of the resulting number is 1, 3, 6 or 8 for the truthy strings, and doesn't give any of those values for the falsy strings. So it can be used as a signature. We thus perform modulo 13 and see if the result is any of those four values. This gives 1 if it is, or 0 otherwise.

The final result should be truthy if any of the two conditions is met, and falsy otherwise. So we add the two numbers resulting from 1 and 2 above and convert to logical, which gives 1 or 0 as standardized truthy/falsy values.

Answer 2

Retina, 22 24 23 bytes

Saved 1 byte thanks to edc65

i`^([-1-9sdty]|fo|n?on)

The whole code is just a regex. The i` at the start makes the regex case insensitive.

Outputs 1 for truthy, 0 for falsey.

Try it online!

Answer 3

Batch, 142 bytes

@goto l%1 2>nul
:l
:l0
:lfailure
:lfalse
:ln
:lnan
:lnil
:lno
:lnotfound
:lnot-found
:lnull
:lnullptr
:loff
:lundefined
@echo 1

Outputs 1 for falsy, nothing for truthy.

Answer 4

JavaScript (ES6), 35 39

Edit using the n?on trick, stolen from BusinessCat's answer

Edit 2 OP clarified, no leading 0s, saved 4 bytes

v=>/^([-1-9dsty]|fo|n?on)/i.test(v)

Simply returns true or false

Test

f=v=>/^([-1-9dsty]|fo|n?on)/i.test(v)

trues=[-1,1,1234,-4321,'defined','deFined','Found',
'nonnil','non-nil','ON','SuCCess','T','true','y','YeS']
falses=[0,'','faLSE','f','Failure','n','NaN','nil',
'no','notfound','not-Found','NULL','nullptr','OFF','unDefined']

console.log('TRUE: '+trues.map(x=>f(x)))

console.log('FALSE:' +falses.map(x=>f(x)))

Answer 5

Python, 111 bytes

def b(s):s=s.lower();return s!='no'and not sum(map(ord,s))in[0,48,323,744,523,877,110,785,443,922,315,317,946]

Tests on sum of ASCII values, extra check for no since on has the same value.

• Edit1: forgot to test on integer values. Now checking for false inputs

Answer 6

Python, 129 79 78 bytes

Gotta submit fast!

lambda n:n.lower()[:3]in" 0 f n no nil fai fal nan not nul off und".split(" ")

True is false and false is true; I have a nice rhyme for this, I really do (not)

Answer 7

Python, 83 75 bytes

import re
def f(s):return re.search(r'^([-1-9dsty]|fo|n?on)',s.lower()).pos

Returns 0 on success, AttributeError on failure.

Now using edc85's regex to save 8 bytes.

Answer 8

PowerShell v2+, 39 37 bytes

$args[0]-match'^([-1-9dsty]|fo|n?on)'

Presumes that the answer to @feersum's question is "No, truthy integers may not start with a 0."

Port of @edc65's regex JavaScript answer, with my own 1-9 substitution instead of \d. Uses @BusinessCat's n?on trick to golf further.

Outputs literal Boolean $true or $false values, which when left on the pipeline and sent through an implicit Write-Output at the end of execution results in True or False being printed to the console.

---

If the answer is "Yes, truthy integers can start with 0," then the following changes need to be made for 51 49 bytes

param($n)$n-ne0-and$n-match'^([-\ddsty]|fo|n?on)'

---

If you don't like regex, go for PowerShell v3+ and the following at 107 bytes

param($n)$n-and$n-notin-split'0 f failure false n nan nil no notfound not-found null nullptr off undefined'

This takes the string of falsey values, -splits them on whitespace, and uses the -notin operator to check the input $n against that array of strings (which is, by default, case-insensitive). Requires the $n-and to check against the empty string.

Answer 9

PHP, 50 bytes

<?=preg_match('%^([-1-9dsty]|fo|n?on)%i',$argv[1])

prints 1 for truthy, nothing for falsy

tried to come up with a different solution, but the shortest regex for falsy is 3 bytes longer than that for truthy: %^(0|fa|f?$|n(?!on)|of|u)%i

Answer 10

Zsh, 32 bytes

grep -Pi '^([-1-9dsty]|fo|n?on)'

Try it online!

Outputs via exit code; 0 is truthy, 1 is falsey

Answer 11

Python, 83 bytes

lambda x:x.lower()[:3]in['fou','non','on']or x[:1].lower()in'dsty-123456789'and''<x

https://repl.it/ClgO/1