Re: Data transformation templates

[Javier Guerra Giraldez <javier@...>]

On Wed, Jan 8, 2014 at 8:16 AM, Alexander Gladysh <agladysh@gmail.com> wrote:
> I'd like to write this declaratively. Maybe like this:
>
> local result = T:map (data)
> {
>   sprite = "/img/" .. T(1);
>   x = T(2), y = T(3);
> }

what's wrong with the classic map(t,f) transformation?

function map(t,f)
    local o={}
    for i = 1,#t do
        o[i] = f(t[i])
    end
    return o
end

local result = map(data, function(e) return {
    sprite = '/img/'..e[1],
    x = e[2], y = e[3]
})



i guess for complex mappings a naïve map(t,f) doesn't cut it, but a
template wouldn't either....

or maybe you want to do it at compile time to avoid runtime delay?  i
typically get it just by calling any startup transformation on the
module itself, not on any function.

or you just want very high performance, avoiding the n function calls
overhead?  i've done simple things like:

function buildmap(b)
    return loadstring([[
        function (t)
            local o = {}
            for i = 1, #t do
                local in,out = t[i], nil
                ]]..b..[[
                o[i] = out
            end
        return o
    ]])
end

buildmap([[
    out = {
        sprite = '/img/'..in[1],
        x = in[2], y = in[3]
    }
]])(data)

but i don't like it...

-- 
Javier