type checking helper with Ramda

Question

I want to write a function whose specifications is described in the piece of code below which is the current implementation I have. It does work. However I have been trying for a while to write it pointfree and entirely as a composition of ramda functions and could not find a solution. The issue is linked to obj => map(key => recordSpec[key](obj[key]) which I cannot reduce in a way that I can write the whole thing pointfree.

How could I do?

/** * check that an object : * - does not have any extra properties than the expected ones (strictness) * - that its properties follow the defined specs * Note that if a property is optional, the spec must include that case * @param {Object.<String, Predicate>} recordSpec * @returns {Predicate} * @throws when recordSpec is not an object */ function isStrictRecordOf(recordSpec) { return allPass([ // 1. no extra properties, i.e. all properties in obj are in recordSpec // return true if recordSpec.keys - obj.keys is empty pipe(keys, flip(difference)(keys(recordSpec)), isEmpty), // 2. the properties in recordSpec all pass their corresponding predicate // For each key, execute the corresponding predicate in recordSpec on the // corresponding value in obj pipe(obj => map(key => recordSpec[key](obj[key]), keys(recordSpec)), all(identity)), ] ) }

For instance, isStrictRecordOf({a : isNumber, b : isString})({a:1, b:'2'}) -> true isStrictRecordOf({a : isNumber, b : isString})({a:1, b:'2', c:3}) -> false isStrictRecordOf({a : isNumber, b : isString})({a:1, b:2}) -> false

Answer 1

One way to achieve this would be to use R.where, which takes a spec object like your recordSpec and applies each predicate with the value from the corresponding keys of the second object.

Your function would then look like:

const isStrictRecordOf = recordSpec => allPass([
  pipe(keys, flip(difference)(keys(recordSpec)), isEmpty),
  where(recordSpec)
])