Curry function

Curry.md

From Mason Protter in Slack:

struct FullyCurried end

macro curried(fdef)
    f = fdef.args[1].args[1]
    fargs = fdef.args[1].args[2:end]
    arity = length(fargs)
    body = fdef.args[2]
    err_str = "Too many arguments. Function $f only takes $arity arguments"
    quote 
        begin 
        function $f(args...)
            if length(args) < $arity
                x -> $f((args..., x)...)
            elseif length(args) == $arity
                $f(FullyCurried(), args...)
            else
                throw($err_str)
            end
        end
        $f(::FullyCurried, $(fargs...)) = $body
        end
    end |> esc
end

@curried foo(x, y, z) = (x^2 + y^2)/(x^2 + y^2 +z^2)

julia> foo(1)(2)(3)
0.35714285714285715

julia> foo(1, 2, 3)
0.35714285714285715```