Hi, Just for the record :)
On Thu 23 Jul 2009 18:13, Mark H Weaver <m...@netris.org> writes: > On Thu, Jul 23, 2009 at 05:24:30PM +0200, Marijn Schouten (hkBst) wrote: >> For the calls above all the dynamic accesses can be determined statically. >> Lexical accesses can always be determined statically. Thus all accesses in >> this >> example can be determined statically and can be compiled to a location >> dereference (either read or write). Nothing in the semantics is inherently >> inefficient. > > There is at least one inherent loss of efficiency with the semantics > you propose: with a lexical-let binding, the compiler can determine > statically whether the variable is non-mutable, because the only place > it could possibly be set! is within the lexical scope. Non-mutable > variables can safely be inlined, an especially important optimization, > especially if the value is a procedure. Guile does detect this. The useful optimization is that variables that are never set! can be allocated on the stack, and if they're closed over, they can simply be copied. > Also, with lexical-let, the compiler knows statically the entire set > of references, which can be helpful with many analyses, for example > whether continuations or closures can "escape" a particular scope, > whether a particular continuation might be invoked more than once, > etc. This is a more tricky optimization :) Andy -- http://wingolog.org/
