Currying transforms a multi-argument function into a sequence of functions that can receive arguments incrementally. In Ruby, Proc#curry uses a function's arity to delay evaluation until enough arguments arrive, returning another function along the way. section 16.3.4 section 16.3.5
Currying becomes clearer when contrasted with partial function application:
- Partial application accepts fewer than the function's required arguments, evaluates the supplied portion, and returns one function for the remainder. section 16.3.5
- Currying returns a series of functions, each taking one argument; Ruby's curry method supports both this behavior and partial application. section 16.3.5
- Curried functions can be called directly with all arguments, incrementally with chained calls, or in mixed groups. section 16.3.5
Reusing a generic filtering function
Instead of defining separate functions for multiples of 3 and 5, define `find_multiples = -> (x, arr) { arr.select { it % x == 0 } }`. Calling `find_multiples.curry` and supplying 3 or 5 creates reusable functions that later accept an array and select its multiples. section 16.3.5
>> find_multiples_of = find_multiples.curry
>> find_multiples_of_3 = find_multiples_of.(3)
>> find_multiples_of_5 = find_multiples_of.(5)
Inspect the staged construction of specialized functions from a curried generic function, then apply them to arrays. section 16.3.5
