Clojure: function composition at runtime

Question

Problem:

Suppose I have a set of functions f_1 ... f_n that I want to compose at runtime, such that I get for example:

(f_a (f_b (f_c) (f_d)) (f_e))

Therefore I need the types of the parameters and the return value of each function in order to know, which functions I can plug into each other.

First Attempt: Annotate each function

(defn foo [n f]
  ^{:params [Number clojure.lang.Fn]
    :return String}
  (do stuff with f and n, return a string))

I don't like this approach because of obvious reasons, such as if I wanted to use clojure.core as the set of functions I would have to annotate every function, which wouldn't be very desirable.

Questions

1. How would you attempt to solve this problem?

2. Could core.typed help me with that?

Answer 1

I do similar things when composing the search query to pass to solr and use a map for the arguments to all the functions and have them all return a map with whatever changes the function decided to make contained in the map, and everything else returned unchanged. So in short i would:

1. use a map for the input and output of every function
2. core.typed is not helpful because everything is a map
3. prismatic.schema is very helpful because you can use it to know what keys are required and to write tests that validate the structure of these maps.

Projects/people with more of an inclination to statically typed functional languages will likely turn to monads in cases like this because they are a powerful tool for describing composition in a type safe way.