From bb0c8157411586fa9bb661cf9497892a1b3f7c90 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Sun, 13 Jun 2010 20:17:49 +0200
Subject: [PATCH] attempted microoptimization in eval.scm.

* module/ice-9/eval.scm (primitive-eval): Try using list-ref instead of
  cdring in the vm. We'll check the hydra build times to see if this has
  any actual merit. Surely the best solution is another representation
  of environments, though.
---
 module/ice-9/eval.scm | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/module/ice-9/eval.scm b/module/ice-9/eval.scm
index c16f08e77..30a373a7a 100644
--- a/module/ice-9/eval.scm
+++ b/module/ice-9/eval.scm
@@ -46,6 +46,9 @@
 (eval-when (compile)
   (define-syntax capture-env
     (syntax-rules ()
+      ((_ (exp ...))
+       (let ((env (exp ...)))
+         (capture-env env)))
       ((_ env)
        (if (null? env)
            (current-module)
@@ -340,11 +343,8 @@
     (define (eval exp env)
       (memoized-expression-case exp
         (('lexical-ref n)
-         (let lp ((n n) (env env))
-           (if (zero? n)
-               (car env)
-               (lp (1- n) (cdr env)))))
-      
+         (list-ref env n))
+        
         (('call (f nargs . args))
          (let ((proc (eval f env)))
            (call eval proc nargs args env)))
@@ -353,10 +353,10 @@
          (variable-ref
           (if (variable? var-or-sym)
               var-or-sym
-              (let lp ((env env))
-                (if (pair? env)
-                    (lp (cdr env))
-                    (memoize-variable-access! exp (capture-env env)))))))
+              (memoize-variable-access! exp
+                                        (capture-env (if (pair? env)
+                                                         (cdr (last-pair env))
+                                                         env))))))
 
         (('if (test consequent . alternate))
          (if (eval test env)
@@ -391,10 +391,7 @@
       
         (('lexical-set! (n . x))
          (let ((val (eval x env)))
-           (let lp ((n n) (env env))
-             (if (zero? n)
-                 (set-car! env val)
-                 (lp (1- n) (cdr env))))))
+           (list-set! env n val)))
         
         (('call-with-values (producer . consumer))
          (call-with-values (eval producer env)
@@ -416,10 +413,10 @@
          (variable-set!
           (if (variable? var-or-sym)
               var-or-sym
-              (let lp ((env env))
-                (if (pair? env)
-                    (lp (cdr env))
-                    (memoize-variable-access! exp (capture-env env)))))
+              (memoize-variable-access! exp
+                                        (capture-env (if (pair? env)
+                                                         (cdr (last-pair env))
+                                                         env))))
           (eval x env)))
       
         (('dynwind (in exp . out))