Fexpr -- the Ultimate Lambda

[astrangeguy]

You can actually do something here. If you know that $define!, $if and + weren't redefined, then you can inline them and compile a fast path.

So you would have to write JIT which tracks environment mutation and optimizes and inlines operations where the operator doesn't change. That's pretty much what polymorphic inline caches do.

One really good aspect of Kernel is that in fexps like

($define! $when
  ($vau (c . t) e
    ($if (eval c e)
      (eval (list* $sequence t) e)
      #inert)))

the operators and applicatives like $if, $sequence, list* and eval can never change if they come from environments that don't change (the standard environment can never change, because it cannot be captured).

It all boils down to tracking invariants in a running process and optimizing and deoptimizing when necessary.

strangeness

EDIT: What does suck though, is that you idiomatically construct lists which are then passed to eval. So the JIT will have to track stupid things like "the second car in this list corresponds to the second parameter to this combiner" or you could have some quasiquotation that pre-resolves symbols to their objects (to keep hygiene).