From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Fri, 9 Dec 2011 21:20:51 +0000 (+0530)
Subject: solution to 4.14
X-Git-Url: https://git.rkrishnan.org/listings/vdrive/%3C?a=commitdiff_plain;h=97b06c1122821e2453ede0c458b818438cb67ff2;p=sicp.git

solution to 4.14
---

diff --git a/src/sicp/ex4_14.rkt b/src/sicp/ex4_14.rkt
new file mode 100644
index 0000000..01cf157
--- /dev/null
+++ b/src/sicp/ex4_14.rkt
@@ -0,0 +1,47 @@
+#lang racket
+
+#|
+
+promitive procedures are applied as follows:
+
+(define (apply-primitive-procedure proc args)
+  (apply-in-underlying-scheme
+   (primitive-implementation proc) args))
+
+Let us say that we have added `map' as a primitive procedure. It is represented as
+('primitive map)
+
+(primitive-implementation)
+
+> (define primitive-procedures
+  (list (list 'car car)
+        (list 'cdr cdr)
+        (list 'cons cons)
+        (list 'null? null?)
+        (list 'map map)
+        ))
+> (define (primitive-procedure-names)
+  (map car
+       primitive-procedures))
+> (primitive-procedure-names)
+'(car cdr cons null? map)
+> (define (primitive-procedure-objects)
+  (map (lambda (proc) (list 'primitive (cadr proc)))
+       primitive-procedures))
+> (primitive-procedure-objects)
+'((primitive #<procedure:car>) (primitive #<procedure:cdr>) (primitive #<procedure:cons>) (primitive #<procedure:null?>) (primitive #<procedure:map>))
+
+> (apply (primitive-implementation (list 'map map)) (primitive-implementation (list 'car car)) '(((1 2 3) (3 4 5))))
+'(1 3)
+> (apply (primitive-implementation (list 'primitive map)) (primitive-implementation (list 'primitive car)) '(((1 2 3) (3 4 5))))
+'(1 3)
+> (apply (primitive-implementation (list 'primitive map)) (list 'primitive car) '(((1 2 3) (3 4 5))))
+map: expects type <procedure> as 1st argument, given: '(primitive #<procedure:car>); other arguments were: '((1 2 3) (3 4 5))
+> 
+
+If we apply primitive procedures to our primitive map, it fails because it cannot understand our primitive representation.
+In general, all primitive versions of higher order functions fail when passes a primitive procedure.
+
+If we are implementing Scheme using a Lisp other than Scheme itself (say, Clojure) then we will be passing Scheme functions
+to the Clojure's map, which is not guaranteed to work because of the different syntax.
+|#
\ No newline at end of file