Conditionals (if-else) and Loops about cgt

[nickjhay]

Clojure also used the special case approach to solving conditionals (see special forms in the description of evaluation), where for certain functions evaluation of the arguments occurs in an unusual order, rather than implementing thunks. Thunks seem to add unnecessary overhead to this basic operation.

I haven't used Theano much, but it looks like much of the functionality of scan could be implemented by a combination of map and reduce into something like a transducer:

transduce(f, v, []) = (v, [])
transduce(f, v, x:xs) =
    let (v', y) = f(v,x) in
        let (v_final, ys) = transduce(f, v', xs) in
            (v_final, y:ys)

map(f, ys) = transduce(\_,x -> (nil, f(x)), nil, ys)[1]
reduce(f, v, ys) = transduce(\v,x -> (f(v,x), nil), v, ys)[0]

This seems about as hard to implement as map and reduce.