Type Safe Ramda Functions

[svozza]

As mentioned in #141, let's start try to get a list of typesafe functions we want from Ramda. I've put together a list of way too many functions that we can whittle down here as people chip in with their views.

• R.append
• R.concat
• R.contains
• R.equals
• R.filter
• R.fromPairs
• R.keys
• R.length
• R.max
• R.mean
• R.median
• R.merge
• R.mergeAll
• R.min
• R.modulo
• R.omit
• R.prepend
• R.product
• R.range
• R.reduce
• R.reject
• R.reverse
• R.scan
• R.split
• R.sum
• R.toPairs
• R.trim
• R.values
• R.when
• R.unless
• R.zip
• R.zipObj

Something I'm not clear on though is how we deal with functions that accept both arrays and string. Do we need a new type?

[davidchambers]

I think we can tick the box beside R.nth since we already have S.at.

Is there a reason you included R.when but not R.unless?

Something I'm not clear on though is how we deal with functions that accept both arrays and string. Do we need a new type?

This should be possible. For example:

concat :: Semigroup a => a -> a -> a

[svozza]

I think we can tick the box beside R.nth since we already have S.at.

Ah yes, of course.

Is there a reason you included R.when but not R.unless?

Oops, no, just an oversight. Fixed.

[jethrolarson]

I assume that your concat would ensure that both arguments are the same type, right?

[davidchambers]

I assume that your concat would ensure that both arguments are the same type, right?

That's right, @jethrolarson:

const $ = require('sanctuary-def');

const def = $.create(true, $.env);

//    a :: Type
const a = $.TypeVariable('a');

//    Semigroup :: TypeClass
const Semigroup = $.TypeClass(
  'sanctuary/Semigroup',
  x => x != null && typeof x.concat === 'function'
);

//    concat :: Semigroup a => a -> a -> a
const concat =
def('concat',
    {a: [Semigroup]},
    [a, a, a],
    (x, y) => x.concat(y));

concat('abc', 'def');
// => 'abcdef'

concat([1, 2, 3], [4, 5, 6]);
// => [1, 2, 3, 4, 5, 6]

concat('abc', [1, 2, 3]);
// ! TypeError: ‘concat’ expected a value of type String as its second argument; received [1, 2, 3]

concat(['a', 'b', 'c'], [1, 2, 3]);
// ! TypeError: ‘concat’ expected a value of type (Array String) as its second argument; received [1, 2, 3]

[svozza]

So, I'm trying to implement S.length and this issue of types that work on lists and strings won't be resolved by relying on the Semigroup type. If we restrict S.length in this way then that means that the function should work on Either types, which of course don't have a length property. It also means that it won't operate on the Function type. If we could treat strings as lists of characters then we could just use the Functor type class but that's not an option here.

[jethrolarson]

Yeah, semigroup doesn't give you index or length. Array-like does but
that's not mathy :)

On Sun, Feb 28, 2016, 3:42 AM Stefano Vozza [email protected]
wrote:

So, I'm trying to implement S.length and this issue of types that work on
lists and strings won't be resolved by relying on the Semigroup type. If
we restrict S.length in this way then that means that the function should
work on Either types, which of course don't have a length property. It
also means that it won't operate on the Function type. If we could treat
strings as lists of characters then we could just use the Functor type
class but that's not an option here.

—
Reply to this email directly or view it on GitHub
#145 (comment).

[svozza]

Ha. Yes, I was hoping not to go down that route...

[joneshf]

Array-like can mostly be approximated by Foldable because you can define toArray: https://github.com/fantasyland/fantasy-land/#foldable

So you could have length. Though i'm not exactly sure how to type it with sanctuary-def:

// length : Foldable f => f a -> NonNegativeInteger
function length(x) {
  return x.reduce((state, _) => state + 1, 0);
}

Are there any examples in sanctuary-def of typeclasses with higher kinded types? I see the test for Monad, but it's a test of the bad case.

[davidchambers]

One straightforward solution is a "Countable" type class which checks whether a given value has a valid length property. I like where @joneshf is going with Foldable, though.

Are there any examples in sanctuary-def of typeclasses with higher kinded types?

I believe higher-kinded types to be doable, but sanctuary-def doesn't yet support them.

[svozza]

Something that was mentioned in the Gitter room was how this issue is a good gateway for people looking to contribute for the first time. It got me thinking that it might be cool to do what they do on the nodejs project and split some of this function list into individual issues and label them with the tag 'good first contribution' like this. What do people think?

[davidchambers]

Great idea, Stefano!

[gilligan]

yeah these are totally "low hanging fruits" and I really like that suggestion Stefano ;)

[davidchambers]

I'll close this issue. We've added many of the important functions, and #216 will add a handful more. Don't hesitate to open an issue if there's a particular Ramda function you'd like sanctified. :)

[futpib]

@davidchambers, do you have something like R.fromPairs?

[davidchambers]

Sanctuary doesn't yet provide such a function, @futpib. Are you interested in working on a pull request to add it?

[futpib]

@davidchambers #454 poof

[Fl4m3Ph03n1x]

Why was R.modulo removed?

[davidchambers]

Why was R.modulo removed?

Because sanctuary-int provides both rem and mod. :)