Arc Forumnew | comments | leaders | submitlogin
1 point by elibarzilay 5262 days ago | link | parent

Fexprs are very different from macros. Not having them is considered by most people as a feature, not a wart. In fact, the common approach to fexprs is a wart. One implication is that eval, as implemented in MzScheme and in Arc is doing the right thing. (And macros are much more well behaved than fexprs, which keeps the language sane.)


1 point by akkartik 5262 days ago | link

I don't follow. Are modern lisps not using f-exprs?

If so I have been imprecise. I was using Alan Kays quote to refer to lisp's special-forms and their many rules on what gets evaluated in what position when.

-----

2 points by elibarzilay 5261 days ago | link

No, modern lisps don't do that. (Except maybe for newlisp, which does what you'd call "the right thing" with `eval`, and even encourages doing so; but this goes with the fact that it throws lexical scope out the window.)

As for the quote, it depends on how you view it. You can take it anywhere to proper criticism of fexprs (which has become the popular view since then), or you can take it as criticizing the fact that special forms are needed, or if you squint hard enough, you can say that it's advocating a language like Haskell. Considering the first two options, I think that the first one (criticism of fexprs) is very explicit, the second one is less likely.

In any case, trying to get an `eval` that works with lexical scope is related to fexprs. So the feature that you want is one that Kay criticizes.

-----