How to make it point-free when there is local variable?

Question

I have a code snippet to remove the host part from server URL in OpenAPI definition. I don't know how to make it point-free totally. (It isn't necessary to do that. But I just want to know how to.)

The difficult part to me is to get rid of the local variable idx. I read this SO and it seems that ap can solve. I didn't try because there is no ap in lodash.

const convert = _.flow([
  _.split('/'),
  (segments) => {
    const idx = _.findLastIndex(containAny(['{', '}', ':']))(segments);
    return _.drop(idx+1, segments);
  },
  _.reject(_.isEmpty),
  _.join('/'),
  path => '/' + path,
]);

Full code:

const _ = require('lodash/fp');

const urls = [
  'http://localhost:8080/petstore/v1',
  '//localhost/petstore/v1',
  '{server}/batch-service/api/batches/lwm2m/v1',
  'https://{server}/batch-service/api/batches/lwm2m/v1',
  '/batch-service/api/batches/lwm2m/v1',
  '/',
]

const containAny = patterns => str => _.some(pattern => _.includes(pattern, str), patterns);

const convert = _.flow([
  _.split('/'),
  (segments) => {
    const idx = _.findLastIndex(containAny(['{', '}', ':']))(segments);
    return _.drop(idx+1, segments);
  },
  _.reject(_.isEmpty),
  _.join('/'),
  path => '/' + path,
]);

_.map(convert)(urls);

Answer 1

In your case you need to call _.findLastIndex() on segments, and then call _.drop() on the results of the find and segments:

drop(findLastIndex(segments))(segments)

Which is equivalent to the chain combinator function:

const chain = f => g => x => f(g(x))(x);

Lodash/fp accepts all functions when using _.flow() (which is also a functional combinator), so you can create other functional combinators, and use them.

const chain = f => g => x => f(g(x))(x);

const containAny = patterns => str => _.some(pattern => _.includes(pattern, str), patterns);

const findLastSegmentIndex = _.flow(
  _.findLastIndex(containAny(['{', '}', ':'])),
  _.add(1)
)

const convert = _.flow([
  _.split('/'),
  chain(_.drop)(findLastSegmentIndex),
  _.reject(_.isEmpty),
  _.join('/'),
  path => '/' + path,
]);

const urls = [
  'http://localhost:8080/petstore/v1',
  '//localhost/petstore/v1',
  '{server}/batch-service/api/batches/lwm2m/v1',
  'https://{server}/batch-service/api/batches/lwm2m/v1',
  '/batch-service/api/batches/lwm2m/v1',
  '/',
];

const result = _.map(convert)(urls);

console.log(result);

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