I’d like to try and concoct a question to the panel around Cake, Reader, modules/objects. The following is all I have so far:
Something I’ve noted is that folks are happy to allow the compiler to lambda lift for them (to eliminate free variables and make functions “top level”):
for example:
– listing 1: let makeAdder n = -> x + n let adder = makeAdder 10 adder 1 => 11 adder 2 => 12
translates after lambda lifting to something like:
– listing 2: let top x n = x + n data Closure t = Closure {v :: t, f :: t -> Integer -> Integer} let makeAdder n = Closure n topLevel let adder = makeAdder 10 (f adder) (v adder) 1 => 11 (f adder) (v adder) 2 => 12
Reader is a similar concept to me — a free variable (often “config”) that can be accessed across many top level functions. However, directly using Reader seems a little like using the encoding in listing 2 above. I’m wondering if a tool — perhaps a compiler — could take care of those details just like the lowering that happens with lambda-lifting.
This may be related to the idea of “algebraic effects” and overcoming the composabilty problem with monad transformers. I don’t understand the details but here are a couple of references.
http://edwinb.wordpress.com/2013/03/28/programming-and-reasoning-with-algebraic-effects-and-dependent-types/ http://math.andrej.com/2012/03/08/programming-with-algebraic-effects-and-handlers/