[Caml-list] unboxing of unary datatypes

[Hal Daume III <hdaume@ISI.EDU>]

Hi all,

I originally had a very calculation intensive program which used a data
type which looked like:

> type foo = Foo of float

I could just have easily used floats, but I wanted to ensure that I didn't
do anything stupid (like try to multiply a foo by a float), so I did this
boxing so the type-checker would help me out.

I had always assumed that once the code got past the typechecker, the
ocaml compiler would optimize away the constructor, so that the resulting
code would be as efficient as if I had just done

> type foo = float

But based on some non-scientific tests, it seems that this isn't the case,
and that the original foo type is actually represented using a
pointer-to-float.

I cannot imagine why this is the case (coming from a Haskell world, there
is a difference there between these two types due to laziness, but since
ocaml is strict, I figured this wouldn't be the case).

Can someone explain this to me?  Why doesn't the compiler optimize out the
constructor?

 - Hal

--
Hal Daume III

 "Computer science is no more about computers    | hdaume@isi.edu
  than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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