CODEWITHSUNDEEP
conditional-statementsramda.js
user2504831
user2504831

Reputation: 157

Ramda: condition statement issue

I tried to set a condition statement using R.cond. Firstly, i got the array size according to the input (i.e. [1,2,3]), then check if the array size is greater / equal to the input size (i.e. 3). But i got an error message. I would like to know why the error occur and how to fix it, thanks.

R.cond([
  [R.compose(R.gte, R.length), () => {console.log(1)}],
  [R.T, () => {console.log(2)}]
])([1,2,3])(3)

Error message: R.cond(...)(...) is not a function

Upvotes: 2

Views: 2827

Answers (1)

Scott Sauyet
Scott Sauyet

Reputation: 50807

I think there are two separate issues here. First of all, because the vast majority of calls to cond-functions are unary, it does not curry the result.

So you cannot call it as (...)([1,2,3])(3). You will need to do (...)([1,2,3], 3).

But that won't fix the other issue.

compose (and its twin pipe) do take multiple arguments for their first call, but after that only a single argument is passed between them. So the only value being passed to gte is the result of length.

You can fix this in several ways. Perhaps the simplest is:

const fn = R.cond([
  [(list, len) => list.length >= len, always(1)],
  [R.T, always(2)]
]);

fn([1, 2], 3); //=> 2
fn([1, 2, 3], 3); //=> 1

(Note that I changed your console.log to a function that returns a value.)

If you want to make this points-free, you could switch to use Ramda's useWith like this:

const fn = R.cond([
  [R.useWith(R.gte, [R.length, R.identity]), always(1)],
  [R.T, always(2)]
]);

But as often happens, I think the introduction of arrow functions makes tools like useWith less helpful. I find the earlier version more readable.

You can see these in action on the Ramda REPL.

Upvotes: 2

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