Lambda the Ultimate

I was googling for deforestation haskell and came across the principal investigator's blog. From the paper:

Abstract. Haskell is a functional language, with features such as higher order functions and lazy evaluation, which allow succinct programs. These high-level features are difficult for fast execution, but GHC is a ma- ture and widely used optimising compiler. This paper presents a whole- program approach to optimisation, which produces speed improvements of between 10% and 60% when used with GHC, on eight benchmarks.

While nominally part of the YHC project, Haskell -011 is currently a Haskell to Haskell transformer that feeds GHC.

I've been on this topic for about twenty four hours now: what are first class functions? I think the answer is "functions are first class when they are part of the world of expressions" (as opposed to the world of statements). No one I've spoken with agrees, though -- many of them suggest that syntax transformation is enough. What do you think?