On Mon, Apr 09, 2012 at 07:37:48AM +0200, Cedric Cellier wrote:
> > - Chung-chieh Shan and Oleg's "Lightweight Static Capabilities"
> > presents several examples of phantom types and a general design method
> > to use them to enhance program safety:
> > http://okmij.org/ftp/papers/lightweight-static-capabilities.pdf
>
> I attempted to read this one out of curiosity,
> and it raised a question: is there a way to write
> these unsafe functions (List.Unsafe.tail/head...) in pure OCaml?
It depends on what you call "pure OCaml". Using the evil Obj module:
let head (l : 'a list) : 'a = Obj.obj (Obj.field (Obj.repr l) 0) ;;
which relies on the underlying representation (use at your own risks) and
generates a call to caml_array_unsafe_get:
L1: const 0
push
acc 1
ccall caml_array_unsafe_get, 2
return 1
Similarly:
let tail (l : 'a list) : 'a list = Obj.obj (Obj.field (Obj.repr l) 1) ;;
Best,
--
Gabriel
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