March 2014 update

Task/Runtime-evaluation-In-an-environment/TXR/runtime-evaluation-in-an-environment-1.txr

@@ -0,0 +1,5 @@
+(defun eval-subtract-for-two-values-of-x (code-fragment x1 x0)
+  (- (eval ^(let ((x ,x1)) ,code-fragment))
+     (eval ^(let ((x ,x0)) ,code-fragment))))
+
+(eval-subtract-for-two-values-of-x 1 2) ;; yields -4.67077427047161

Task/Runtime-evaluation-In-an-environment/TXR/runtime-evaluation-in-an-environment-2.txr

@@ -0,0 +1,7 @@
+(defun eval-subtract-for-two-values-of-x (code-fragment x1 x0)
+  (let ((e1 (make-env (list (cons 'x x1))))   ;; create two environments stuffed with binding for x
+        (e0 (make-env (list (cons 'x x0)))))
+    (- (eval code-fragment e1)                ;; pass these environment to eval
+       (eval code-fragment e0))))
+
+(eval-subtract-for-two-values-of-x '(exp x) 1 2)

Task/Runtime-evaluation-In-an-environment/TXR/runtime-evaluation-in-an-environment-3.txr

@@ -0,0 +1,9 @@
+(defun eval-subtract-for-two-values-of-x (code-fragment x1 x0)
+  (let ((e1 (make-env))
+        (e0 (make-env)))
+    (env-vbind e1 'x x1)
+    (env-vbind e0 'x x0)
+    (- (eval code-fragment e1)
+       (eval code-fragment e0))))
+
+(eval-subtract-for-two-values-of-x '(exp x) 1 2)

Task/Runtime-evaluation-In-an-environment/TXR/runtime-evaluation-in-an-environment-4.txr

@@ -0,0 +1,7 @@
+(defvar x)
+
+(defun eval-subtract-for-two-values-of-x (code-fragment x1 x0)
+  (- (let ((x x1)) (eval code-fragment))
+     (let ((x x0)) (eval code-fragment))))
+
+(eval-subtract-for-two-values-of-x '(exp x) 1 2)