Extract file extension: Difference between revisions
→{{header|javascript}}: Added a reusable (OS-independent) function
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Line 917:
document.txt_backup ->
/etc/pam.d/login -> </pre>
With JS embedded in browsers and other applications across most or all operating systems, we need some flexibility in any reusable '''takeExtension''' function.
One approach is to define a more general curried function, from which we can obtain various simpler and OS-specific functions by specialisation:
<lang javascript>(() => {
'use strict';
// OS-INDEPENDENT CURRIED FUNCTION --------------------
// takeExtension :: Regex String -> FilePath -> String
const takeExtension = charSet => fp => {
const fs = fp.split('/');
return 0 < fs.length ? (() => {
const
rgx = new RegExp('^[' + charSet + ']+$'),
xs = fs.slice(-1)[0].split('.'),
ext = 1 < xs.length ? (
xs.slice(-1)[0]
) : '';
return rgx.test(ext) ? (
'.' + ext
) : '';
})() : '';
};
// OS-SPECIFIC SPECIALIZED FUNCTIONS ------------------
// takePosixExtension :: FilePath -> String
const takePosixExtension = takeExtension('A-Za-z0-9\_\-');
// takeWindowsExtension :: FilePath -> String
const takeWindowsExtension = takeExtension('A-Za-z0-9');
// TEST -------------------------------------------
// main :: IO()
const main = () => {
[
['Posix', takePosixExtension],
['Windows', takeWindowsExtension]
].forEach(
([osName, f]) => console.log(
tabulated(
'\n\ntake' + osName +
'Extension :: FilePath -> String:\n',
x => x.toString(),
x => "'" + x.toString() + "'",
f,
[
"http://example.com/download.tar.gz",
"CharacterModel.3DS",
".desktop",
"document",
"document.txt_backup",
"/etc/pam.d/login"
]
),
'\n'
)
)
};
// GENERIC FUNCTIONS ----------------------------------
// comparing :: (a -> b) -> (a -> a -> Ordering)
const comparing = f =>
(x, y) => {
const
a = f(x),
b = f(y);
return a < b ? -1 : (a > b ? 1 : 0);
i
};
// compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
const compose = (f, g) => x => f(g(x));
// justifyRight :: Int -> Char -> String -> String
const justifyRight = (n, cFiller, s) =>
n > s.length ? (
s.padStart(n, cFiller)
) : s;
// Returns Infinity over objects without finite length.
// This enables zip and zipWith to choose the shorter
// argument when one is non-finite, like cycle, repeat etc
// length :: [a] -> Int
const length = xs =>
(Array.isArray(xs) || 'string' === typeof xs) ? (
xs.length
) : Infinity;
// Map over lists or strings
// map :: (a -> b) -> [a] -> [b]
const map = (f, xs) =>
(Array.isArray(xs) ? (
xs
) : xs.split('')).map(f);
// maximumBy :: (a -> a -> Ordering) -> [a] -> a
const maximumBy = (f, xs) =>
0 < xs.length ? (
xs.slice(1)
.reduce((a, x) => 0 < f(x, a) ? x : a, xs[0])
) : undefined;
// tabulated :: String -> (a -> String) ->
// (b -> String) ->
// (a -> b) -> [a] -> String
const tabulated = (s, xShow, fxShow, f, xs) => {
// Heading -> x display function ->
// fx display function ->
// f -> values -> tabular string
const
ys = map(xShow, xs),
w = maximumBy(comparing(x => x.length), ys).length,
rows = zipWith(
(a, b) => justifyRight(w, ' ', a) + ' -> ' + b,
ys,
map(compose(fxShow, f), xs)
);
return s + '\n' + unlines(rows);
};
// take :: Int -> [a] -> [a]
// take :: Int -> String -> String
const take = (n, xs) =>
'GeneratorFunction' !== xs.constructor.constructor.name ? (
xs.slice(0, n)
) : [].concat.apply([], Array.from({
length: n
}, () => {
const x = xs.next();
return x.done ? [] : [x.value];
}));
// unlines :: [String] -> String
const unlines = xs => xs.join('\n');
// Use of `take` and `length` here allows zipping with non-finite lists
// i.e. generators like cycle, repeat, iterate.
// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
const zipWith = (f, xs, ys) => {
const
lng = Math.min(length(xs), length(ys)),
as = take(lng, xs),
bs = take(lng, ys);
return Array.from({
length: lng
}, (_, i) => f(as[i], bs[i], i));
};
// MAIN ---
return main();
})();</lang>
{{Out}}
<pre>
takePosixExtension :: FilePath -> String:
http://example.com/download.tar.gz -> '.gz'
CharacterModel.3DS -> '.3DS'
.desktop -> '.desktop'
document -> ''
document.txt_backup -> '.txt_backup'
/etc/pam.d/login -> ''
takeWindowsExtension :: FilePath -> String:
http://example.com/download.tar.gz -> '.gz'
CharacterModel.3DS -> '.3DS'
.desktop -> '.desktop'
document -> ''
document.txt_backup -> ''
/etc/pam.d/login -> '' </pre>
=={{header|jq}}==
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