On Thu, 2007-10-18 at 11:52 +0200, Tom wrote:
>  Not long ago I was searching the Internet on the topic "combining
>  eager and lazy evaluation", and have run over a paper which I
>  obviously dismissed as "not interesting enough", yet now I have
>  realized that it could indeed be useful, but am unable to find it.
>
>  I know it was talking about a useful primitive, I do not know how
>  exactly it was named, which checked whether values passed as arguments
>  to functions were lazy (blocks to be evaluated) or eager (already
>  evaluated), and using it some functions, e.g. map (this example was
>  present in the paper) could be implemented to be both eager and lazy
>  at the same time, depending on the arguments.
>
>  Does anyone recognize this description?

I guess you mean this one:

  http://web.cecs.pdx.edu/~sheard/papers/ExplicitLazy.ps

The primitive you're alluding to is called "mimic" in it.

- Andreas