Point-free style capitalize function with Ramda

Question

While writing a capitalize function is trivial, such that:

"hello" => "Hello" "hi there" => "Hi there"

How would one write it using point-free style using Ramda JS?

https://en.wikipedia.org/wiki/Tacit_programming

score 14 · Accepted Answer · edited Oct 13 '16 at 04:42

14

It would be something like that:

const capitalize = R.compose(
    R.join(''),
    R.juxt([R.compose(R.toUpper, R.head), R.tail])
);

Demo (in ramdajs.com REPL).

And minor modification to handle null values

const capitalize = R.compose(
    R.join(''),
    R.juxt([R.compose(R.toUpper, R.head), R.tail])
);

const capitalizeOrNull = R.ifElse(R.equals(null), R.identity, capitalize);

edited Oct 13 '16 at 04:42

lorefnon

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answered Oct 13 '16 at 03:33

zerkms

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As a follow-up question, how would you handle the null case when writing in a point-free style? If this function were called with capitalize(null) it will blow up. – Tutan Ramen Oct 13 '16 at 03:49
@TutanRamen prepend it with `ifElse(equals(null), identity, `, otherwise I think that's where `Maybe` monad would become useful. – zerkms Oct 13 '16 at 03:57
Awesome! Can even throw in `isNil` instead of `equals(null)` now! – tmikeschu Apr 19 '18 at 01:02
3

The `ifElse` + `identity` combo could be replaced with the arguably more readable `unless` function: `const capitalizeIfNotNil = R.unless(R.isNil, capitalize);` – Nicolás Fantone May 12 '18 at 01:08

score 13 · Answer 2 · answered Jun 14 '17 at 18:31

13

You can partially apply replace with a Regex that runs toUpper on the first character:

const capitalize = R.replace(/^./, R.toUpper);

answered Jun 14 '17 at 18:31

lax4mike

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Ran some quick and dirty benchmarks on the answers provided, and yours is the fastest. – Christian Bankester Nov 30 '17 at 15:36
the 2nd param to `replace` is a string not a function though. Doesn't work for me – Damian Green Jun 04 '19 at 12:50
@DamianGreen Ramda implement `R.replace` with the native javascript string method. The 2nd argument can be a function too, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace#Syntax – lax4mike Jun 04 '19 at 18:42

score 6 · Answer 3 · answered Oct 13 '16 at 08:55

6

I suggest using R.lens:

const char0 = R.lens(R.head, R.useWith(R.concat, [R.identity, R.tail]));

R.over(char0, R.toUpper, 'ramda');
// => 'Ramda'

answered Oct 13 '16 at 08:55

davidchambers

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score 4 · Answer 4 · answered Nov 30 '17 at 15:41

I put together some quick and dirty benchmarks for anyone interested. Looks like @lax4mike's is fastest of the provided answers (though the simpler, non-point-free str[0].toUpperCase() + str.slice(1) is way faster [and also not what OP was asking for, so that's moot]).

https://jsfiddle.net/960q1e31/ (You'll need to open the console and run the fiddle to see the results)

score 1 · Answer 5 · answered May 12 '18 at 01:34

For anyone reaching this looking for a solution that capitalizes the first letter and also lowercases the rest of the letters, here it is:

const capitalize = R.compose(R.toUpper, R.head);
const lowercaseTail = R.compose(R.toLower, R.tail);
const toTitle = R.converge(R.concat, [capitalize, lowercaseTail]);

toTitle('rAmdA');
// -> 'Ramda'

Point-free style capitalize function with Ramda

5 Answers5